The previous A+ Core Hardware Service Technician exams used to bombard the examinee with questions relating to minute details of the stages of the laser printing electrophotographic process. The current exam may also address some of these details. It is very important that you understand this process and its intricacies, as well as the laser printer paper-feeding process. Equally important, however, is to focus your study on printer troubleshooting and maintenance in general. The current A+ Core test laser printer questions seem to be headed in the direction of the overall use of the technology. For example, you may know that a uniform charge of -600V is applied to the laser printer’s photosensitive drum by the primary corona wire during the conditioning phase of the EP process, but that knowledge will not help you on the test if you can’t answer a question asking you how to dispose of a toner cartridge properly. Show
A laser printer is a popular type of nonimpact printer that is capable of producing resolutions of 1400 dpi or greater, with a usual minimum requirement of 600 dpi. Laser printers use technology similar to that of photocopiers. A laser printer also puts many dots on paper that eventually form an image. Unlike the previously mentioned printing technologies, however, the laser printing process uses plastic toner particles that bond to an electrophotosensitive drum to create an image. These toner particles are actually a combination of organic material, plastic, and iron. A toner cartridge houses the powder toner and is inserted into the laser printer itself. A used toner cartridge should be sent back to the toner cartridge manufacturer for proper disposal or possible refilling. Note for the exam that the toner, paper, and disposable ribbons are considered printer-consumable items. If laser-printed output begins to appear wavy or inconsistent, the problem may be an empty or malfunctioning toner cartridge. The laser printing process begins after you send a document or image from your computer to the laser printer. After the image is accepted by the laser printer, a laser beam and a mirror are used to write an electrostatic representation of the image to a photosensitive drum. The electronically charged drum then rolls through the toner, which adheres to the drum to form an image. At this stage of the process, a sheet of paper is fed into the printer, where it receives an electrostatic charge. The paper is then rolled over to the drum, and the toner image is transferred to the paper. In the next process, the toner is heated and fused to the paper. The final output is directed out of the printer, and the printer awaits the next document or image. This process is repeated every time a page of information is sent to the printer. Printer Quality TypesPrinter quality type standards refer to the quality of the printed dots produced, mainly by dot matrix printers. Printer quality types can also apply to other printing technologies, such as laser printing. You should be familiar with the following printer type qualities for the A+ Core Hardware Service Technician test.
Raster Image ProcessingA raster is a rectangular area or grid of the monitor’s display area used for images or for the mathematically created vector drawing processes. The size of the raster area depends on the resolution of the display area. Monitors use auto sizing to calculate the raster grid size of a display area. A Raster Image Processor (RIP) is used to translate complicated raster images and vector drawings sent to a laser printer. The RIP requires memory to store large images before they are processed. If there is not enough memory in the printer to support the image to be stored, it is more than likely that you will get a “Memory Overflow” error message. Resolution Enhancement Technology (RET) allows a printer to print raster images at a higher resolution than the printer is technically capable of. RET uses a combination of technologies to fill in the spaces between dots on an image for better visual quality. Decreasing the printer’s resolution and decreasing the RET can also help to reduce the frequency of “Memory Overflow” error messages. Laser TechnologiesLaser printer manufacturers utilize different laser printing technologies and processes to attain the same result of producing a high-quality image on final output. For the A+ Core test, we are focusing on the Electrophotographic (EP) process. There are three important laser-printing processes that you should be familiar with.
The EP Laser Printing ProcessThe stages of the EP laser printing process that you need to be familiar with for the A+ Core exam are listed below. Figure 19.5 shows a diagram of the EP laser printing process.
The following alphasupply.com Web site has an excellent laser printing troubleshooting page that lists detailed laser printing problems and solutions in step-by-step detail. This page is definitely worth a look: http://alphasupply.com/printer_problems.htm. Ink DispersionDispersion can be defined as the act of dispersing, which means to separate, distribute, or scatter in different directions. Most printer inks are made up of a combination of ingredients, including pigments, resins, solvents, and varnishes. For a printed document or photo to be clear and precise, it is important that printer ink pigments are dispersed free of lumps and other particles, in a smooth and even manner. Scientifically speaking, ink dispersion has to do with the ink manufacturing and production processes involved with how pigments are separated or broken down from other material. For the A+ exam it is important to note that if ink is improperly dispersed, or if there is a problem with an ink dispersion nozzle (used with most ink-jet printers), printing may become faded or unclear. Dye SublimationDye sublimation technology and dye sublimation printers have brought clear, crisp, photo-quality printing home. With a dye sublimation printer, a heat-sensitive print head moves over a ribbon of transparent film that contains heat-activated inks or sections that represent the four primary printing colors of cyan, magenta, yellow, and black. (CMYK). These solid inks are vaporized and sublimate (adsorb) onto special polymer-coated gloss paper. Here are some important highlights regarding dye sublimation:
In conclusion, the process of dye sublimation produces a smooth, photographic-quality image.
Print, Copy, Fax, and ScanIn the past, the average home or small office required separate devices for such tasks as printing, copying, faxing and scanning. This required enormous amounts of desk/office space, as well as a high cost of ownership and maintenance. Enter the MFD (Multifunction Device)! An MFD is a device that combines the functionality of a printer, a copier, a scanner, and a fax machine into one unit. An MFD has only one warranty, so you don’t need a separate warranty for each of your devices. An MFD is usually connected to a computer system with one cable (usually parallel or USB) and possibly an RJ11 patch for a phone line. An MFD typically requires only one power cord. A networked MFD is typically connected to a switch or router and can be accessed by many users if set up to do so. Most MFDs come with easily installed software packages that allow you set up all of the MFD’s software drivers and functions with minutes. The popularity of MFDs has pretty much flattened the market for single, stand-alone devices. The most popular versions of MFDs offer ink-jet or laser jet technology.
Finishers (Stapling, Etc.)Most high-end printers allow the use of optional units called multifunction finishers. A multifunction finisher is simply a printer-attachable unit that allows some or all of the following options and features:
Most finishers have interfaces that are proprietary to the printer manufacturer, meaning they are not interchangeable between printers. The jamming of staples or paper causes the majority of problems that occur with most finishers. Every manufacturer has its own set of procedures for dealing with these jams. It is advised that you follow the finisher’s manufacturer instructions for finisher-related jams. Important Printer Information and Test TipsThe following printer-related information and test tips are included to ensure that you are well prepared for the many printer-focused questions that may come your way on the real exam:
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CAD/CAMCAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) is a specialized program or graphics software package that works in conjunction with specialized hardware to help architects and manufacturers create and design such things as computers, buildings, and office layouts. CAD/CAM helps with the designing of special-purpose machines for automation. With CAD/CAM, a designer can create, view, and change two-dimensional (2D) and three-dimensional (3D) drawings. The CAD software allows the designer to zoom in, select, and modify particular parts of a design. Several years ago, CAD required specially built computer systems. Today, CAD/CAM software packages are designed to run on multipurpose/multifunctional workstations and servers. The software does, however, have minimum and recommended system requirements. They are: Minimum system requirements:
Recommended system requirements:
To be useful and effective, CAD/CAM programs also depend on specialized input and output devices, such as high-end computer monitors, specialized printers, plotters, digitized tablets, and light pens. For the A+ Core Hardware exam, you do not have to demonstrate that you can create automation equipment using CAD/CAM. What is important is that you understand that CAD/CAM is very graphics intensive and requires as much computer horsepower as you can get your hands on in order to use it effectively. Page 3
This chapter introduced some of the most common types of output devices in use today. You should have paid close attention to monitor types and their associated resolutions, colors, and technologies. At this point, you should also have a good understanding of dot matrix and laser printing technology, including the EP laser printing process. If you have trouble answering the review questions at the end of this chapter, go back and read the chapter again. If you want to pass the A+ Core test, you are going to have to master questions very similar to these questions relating to output devices. Page 4
Answers
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http://alphasupply.com/printer_problems.htm. This alphasupply.com Web site has an excellent laser printing troubleshooting page that lists detailed laser printing problems and solutions in step-by-step detail. Page 6
In Chapter 17 we discussed RAM, which is temporary or primary storage. In this chapter, we discuss forms of permanent or secondary storage devices, such as hard drives, floppy drives, Zip drives, tape devices, and optical storage. Permanent storage devices are sometimes referred to as mass storage or auxiliary storage devices. We also explore the interfaces and technologies used to connect storage devices to a computing system. Some of the more common interfaces are IDE/ATA, serial ATA and SCSI. The core exam is likely to test your knowledge of the proper methods of configuring, connecting, and troubleshooting storage. It seems that the recent A+ Core Hardware exam focused heavily on storage devices. The current test will probably concentrate on your ability to install and configure multiple hard drives, and dwell on the details of SCSI configurations and priorities. Pay close attention to the topics discussed in this chapter; they may make the difference on whether you pass or fail the core exam. THE FLOPPY DRIVEA floppy drive is an internal device that reads or writes information to and from magnetic floppy disks, and communicates with the system’s CPU. The floppy drive is typically mounted into an available drive bay inside the system unit. A floppy drive adapter kit may be necessary if you are installing a floppy drive unit into a large drive bay. Older computing systems used 5.25-inch floppy drives that required a larger bay. Today, most computing systems come with a standard 3.5-inch floppy drive installed. Similar to a hard drive, a floppy disk stores information on magnetic media. A hard drive’s storage medium is called a platter. A floppy drive’s storage medium is called a floppy disk. The major advantage of a floppy disk is that it is portable. You can store files on a floppy disk and take it wherever you go. The major disadvantages of floppy disks are that they are slow to access and cannot store as much information as a hard disk. A floppy disk must receive both a low-level format and a high-level format before it can be considered useful. A low-level format prepares the floppy disk with an organized structure by creating sectors, tracks, and clusters on the floppy disk. A high-level format prepares the floppy disk with a File Allocation Table (FAT) and adds a root directory to it. You can format a floppy from a DOS command prompt or through the use of an operating system GUI, such as Windows. Preformatted floppy disks can be purchased just about anywhere computer supplies are sold. To format a floppy disk from a DOS prompt, simply place the disk in the floppy drive “A” and type “format a:”. A low-level format as well as a high-level format will be carried out on the disk. When the format process is complete, the floppy will be ready to have files saved to it. (See the section “The Hard Drive” later in this chapter for more information on the formatting process.) There are two basic forms of floppy disk media available:
Floppy Drive ComponentsA floppy drive’s components are similar to that of a hard drive. The basic components that make up floppy drives include the read/write heads, which read and write data onto the floppy media and work in tandem with an erase tunnel mechanism to erase information if requested by the floppy drive’s controller. The head actuator, sometimes referred to as a stepping motor, is controlled by the floppy disk controller; it moves the drive’s read/write heads in and out of place. A spindle motor, driven by a belt system, makes the floppy disk spin or rotate at the desired speed. The speed at which the floppy disk spins is measured in revolutions per minute. A floppy drive uses a circuit board, also known as a logic board, which controls all of the floppy drive’s components and communicates with the computer system. Finally, there are two floppy drive connectors. One is used to connect the floppy drive to the system’s power supply, and the other is used to connect the floppy drive to the motherboard’s floppy drive controller. Floppy Drive Configuration and TroubleshootingA floppy drive is connected to a floppy drive controller on the motherboard with a data cable. The data cable has a red stripe that runs down its right side. The red stripe represents pin 1 on the data cable. When plugging the data cable connector into the floppy drive controller on the motherboard, you must match pin 1 on the data cable connector to pin 1 on the controller. The same is true when connecting the other end of the data cable to the floppy drive itself. If you plug the floppy drive’s data cable in backward, the LED light on the front of the floppy drive unit will stay lit, and you will not be able to access the floppy drive. A computer system reserves certain letter designations for its components. The primary hard drive gets the letter designation of C by default. The letters A and B are reserved by the system for assignment to the floppy drives. A typical 3.5-inch floppy drive is attached to the far end of a ribbon data cable (after the twist in the ribbon cable) and gets the letter A assignment. If you have a second floppy drive, such as a 5.25-inch floppy drive, it should be attached to the middle connector on the floppy data cable, and it gets the letter B assignment. Over time, floppy drives and floppy disks can get dirty and warped. This can cause them to fail mechanically or render them incapable of data storage and retrieval. If you attempt to access your floppy drive and receive an error message such as “Drive A is not ready, Abort, Retry or Fail,” either your floppy disk is bad or your floppy drive needs cleaning and/or maintenance. There are times when you may need to boot up your computer with a bootable floppy disk installed in the A drive. This is frequently done for troubleshooting purposes, maintenance, or operating system installation. If you are unable to boot from your bootable floppy disk, check your boot sequence settings in the BIOS configuration and verify that your system is set to boot from the A drive before the C or D drive. Otherwise, the system will not look for your bootable floppy at start-up. One of the most common mistakes people make is to leave a nonbootable floppy disk in a floppy drive when restarting the system. This can cause the error message “Nonsystem disk or disk error; replace and strike any key to continue.” Ejecting the nonbootable floppy from the drive and pressing any key on your keyboard will bypass this error message, and your system will continue to load. (By the way, there is no such thing as an “any” key.) Exchanging floppy disks with others and using them in your system without proper virus protection poses a serious virus threat to your computer. The two most common sources of virus attack come from floppy disks and the Internet. Always scan your floppy media for viruses. Page 7
There have been many names associated with the hard drive since its inception. It has been called the hard disk, the fixed disk, Direct Access Storage Device (DASD), and the C drive. For the purposes of our A+ Core Hardware test study focus, we will use the terminologies hard drive and hard disk. The hard drive is a component attached to a computer system unit in a fixed manner. It is usually installed in a drive bay that is inaccessible from the front of the system unit. When purchasing a computer, it is important to consider a system unit that has enough drive bays available to support multiple hard drives. You may wish to expand your storage capabilities in the future. The hard drive is used as a mass storage device for data and programs. The hard drive is made up of metal platters, a spindle motor, an actuator arm, and a set of read/write heads. Hard drive space is measured in kilobytes, megabytes, and gigabytes. Today’s hard drives generally have a storage capacity between 10GB and 40GB, and rotation speeds between 5200 and 7400 Revolutions Per Minute (rpm). In order for data to be stored, organized, and retrieved from a hard drive in a timely, organized fashion, the hard drive’s media (platters) must be divided into separate tracks, sectors, cylinders, and clusters. The sizes of these separations are collectively known as a hard drive’s geometry. As mentioned earlier, a hard drive’s components are similar to a floppy drive’s. Some of the main components and organizational units that make up a hard drive are listed below.
Hard Drive Partitioning and FormattingTwo primary methods are used to prepare hard drives for supporting operating systems and applications: partitioning and formatting. Without being partitioned and formatted with an organized, logical file structure, a hard drive would be nothing more than a large metal paperweight. A hard drive must have the following processes done to it in order to be useful. PartitioningA hard drive normally receives a low-level format and is partitioned at the factory. If you receive or purchase a hard drive without a preinstalled operating system, you will need to partition and format the drive yourself. Partitioning is the process of dividing one physical hard drive into separate areas of storage. In other words, you can create several logical hard drives out of one physical hard drive. This is useful for file storage purposes, installing multiple operating systems, and supporting multiple file system structures, such as FAT32 and NTFS (NT File System). Two partition types can be created on a hard drive: primary partitions and extended partitions:
DOS, Windows 3x, and the early versions of Windows 95 are FAT16 operating systems, and will allow you to create only a single partition size up to 2GB. If you want to use more than 2GB of hard drive space with these operating systems, you will need to create multiple partitions of 2GB. If you want to use more than 2GB for a single partition on a single hard drive, you will need to use a newer operating system that supports FAT32 or NTFS file systems. Windows 98, Windows 2000, and Microsoft Me allow you to create a single partition of up to 4TB (terabytes). FDISKFDISK is a common DOS utility program that enables the partitioning of a hard drive. FDISK is located on a DOS bootable disk and is run from the command prompt. To use FDISK, simply enter “FDISK” at a command prompt. If your hard drive is larger than 512MB, a menu appears that asks if you would like to enable large disk support. You have the option of replying “Y” for yes or “N” for no. Pressing “Y” accepts the default of yes, and you are presented with the FDISK Options menu. At the FDISK Options menu, you can create one large partition for the whole hard drive. However, if you plan on dividing your hard drive into primary and extended partitions, you will need to use options 1, 2, and 3 to partition the disk accordingly. If you create more than one primary partition, you will need to set one of them as the active, bootable partition. After creating partitions with FDISK and formatting partitions for operating systems and files, you can always use FDISK again to create new partitions. The FDISK Options menu has an option for displaying partition information, which can be a useful tool to assist you with making the right partition choices to suit your needs. Third-party partitioning programs that will allow you to partition a hard drive through the use of a GUI can be purchased.
It is important to note that FDISK has an undocumented switch called /MBR. This switch causes FDISK to write the master boot record to the hard disk without altering partition table information. If you use the command FDISK /MBR, you will replace a systems boot loader with a generic boot loader. This is typically done if the originally installed system boot loader has become corrupted. Many viruses are written to infect a system’s master boot record. Running the FDISK /MBR will also help remove these MBR infector viruses. FormattingBefore an operating system or application can be installed on a partitioned hard drive, the drive must be formatted. Formatting is a two-level process that prepares a partition on a hard drive to accept an operating system, along with files and programs. Two levels of formatting are implemented before the operating system is installed:
FORMAT.COM is a DOS utility program that is also run from the DOS command prompt. The FORMAT command will allow you to format the hard drive in preparation for an operating system. You can also format the hard drive from within an operating system, such as Windows, if the operating system supports FORMAT. From a DOS command prompt, type FORMAT D:You can replace D: in this example with the letter of any drive you wish to format. ScanDisk and DefragOver time, the constant use of your hard drive can cause the sectors to get worn out or damaged. Utility programs such as ScanDisk, Norton Utilities, and Check It are available to help you identify bad sectors on a hard drive. If you are developing bad sectors on your hard drive, it is a good idea to run ScanDisk and select the “Thorough” option in the ScanDisk settings options. This runs a complete scan of your hard drive and attempts to fix any bad sectors it finds. When files are written to a hard drive, they are not stored in contiguous order (one file written directly after another file). Files are stored in a noncontiguous order (anywhere there are available blocks of space). After a while, this can cause the clusters on your drive to become fragmented. It takes time for the CPU to request a file from the hard drive, and it takes even more time if the files are not in any order. Windows offers a built-in utility program called Disk Defragmenter that will help put clusters of files into a contiguous, structured order. Running Disk Defragmenter, or defrag, can increase the disk access time and the overall performance of your system. If a customer complains that his or her system is getting slower over time, running the defragmenter utility will most likely assist you with restoring the customer’s disk access time. It is important to note that Windows 9x, Windows Me, and Windows 2000 offer a built-in defragmenter utility. Windows NT does not. This is discussed in more detail in Part II B of this book. Page 8
A hard drive uses its own internal controller board and processor to manage the interaction of read/write operations. The controller board also provides support for interfaces such as IDE/ATA, EIDE, or SCSI. Before we continue with interface specifications, it is important for you to understand the basic connectors located on a typical hard drive (Figure 20.2). Two main connectors and a set of jumpers are usually located at the rear of the hard drive. The first connector is a 5-pin power connector that receives 5V and 12V DC power from the system’s power supply. The 5V power is the ‘dangerous power’ used by the hard drive’s circuit board. If the 5V power fluctuates, your hard drive’s circuit board and components may be in danger. The 12V power is used to power the hard drive’s motor and actuator heads. The second connector is an IDE 40-pin data connector or an SCSI connector. This connector is used to transmit and receive information and instructions from the computer’s processor. Plastic jumpers are used with IDE interfaces to set the configuration of the hard drive as either a master or a slave drive, along with the use of a data cable that supports multiple or shared interfaces. SCSI devices use plastic jumper blocks to uniquely identify SCSI drives or controller cards. A hard drive communicates with a computer system through the use of an interface. Several communication transfer interfaces and standards ensure that a hard drive will be compatible with a system’s motherboard and processor. These standards are in place to assist manufacturers with a common set of electronic rules for interfaces. ST506 InterfaceNow obsolete, the ST506 was the first standard interface developed in 1980 by Seagate Technologies (ST). This interface required the installer to modify the CMOS configuration manually, provide a low-level format, partition the drive manually, and finally, provide a high-level format. This standard was universally accepted based on its ability to attach to a standard interface data cable. ESDI InterfaceIntroduced in 1983, the Enhanced System Device Interface (ESDI) standard for hard drives was the first interface standard to have a controller actually reside on the hard drive itself. It required a compatible ESDI controller installed on the motherboard. ESDI technology was several times faster than ST506 and was much more expensive as a result. IDE/ATA InterfaceThe IDE/ATA is currently the most widely accepted interface standard. The IDE is an interface controller built into the hard drive. ATA is actually a set of rules or specifications that apply to the IDE controller. The ATA standard is a 16-bit, parallel connection. ATA allows you to have a master drive (drive 0) and a slave drive (drive 1). ATA also provides a way for multiple hard drives to communicate with the same system bus. If your motherboard does not have an IDE/ATA interface, or your system only has one IDE controller, you can purchase an IDE add-on expansion card, such as a PCI card that supports this technology. This will allow you to have up to four devices. One of the major advantages of IDE is that it can provide sector translation. This allows you to change the drive’s properties in CMOS configuration settings. It also allows computer systems to recognize hard drives larger than 528MB by utilizing Logical Block Addressing (LBA) support. LBA is considered a type of IDE transaction. You can enable LBA support, if available, in your BIOS configurations settings for your hard drive. There are two common transfer methods or protocols used to communicate information between memory and an IDE/ATA hard drive controller:
Several improvements have been made to the original implementation of the ATA standard interface. These improvements allow more devices to be attached to an ATA interface and increase the speed at which data can pass between an ATA interface and a device. Some of the ATA standards that you should be familiar with are listed below.
EIDE (Similar To Ata-2) InterfaceEnhanced IDE (EIDE) technology is the same technology as IDE/ATA. It improves on the original IDE standards by allowing ATA drives to utilize PIO modes 3 and 4. An EIDE interface can support up to four drives on the same interface, including CD-ROMs and tape drive units. EIDE uses Advanced Technology Attachment Packet Interface (ATAPI) standards to allow a controller to communicate with CD and tape drive devices. Serial ATA (S-ATA)Just about everything in the computer electronics world eventually evolves into something smaller, faster, and more efficient. This includes the standards for ATA. The Serial ATA (S-ATA) specification is a serial link point-to-point disk-interface connection standard that was developed by the Serial ATA Working Group to overcome some of the limitations of the earlier mentioned ATA (parallel) specifications. Serial ATA is a point-to-point connection that uses a special S-ATA serial cable, which makes use of a minimum of four wires for sending and receiving data. Figure 20.3 displays a Serial ATA cable and connector. Serial is faster than parallel. The clock rate of Serial ATA is a whopping 1.5GHz (150Mbps). Here are some very important points to remember regarding the new Serial ATA specification:
Make sure that you are familiar with the important points mentioned in this section. It is very likely that you will run across them in the exam room. If you are interested in obtaining more information regarding Serial ATA, the following Tom’s Guides Publishing site has an excellent description of Serial ATA: http://www4.tomshardware.com/storage/20020812/. The Serial ATA Working Group page is also quite informative: http://www.serialata.org/. SCSI InterfaceIf you need more than four devices and want the fastest throughput available for storage devices, then an SCSI chain is what you want. An SCSI chain is a group of SCSI devices attached together with a centralized SCSI controller that requires only one IRQ for the entire chain of devices. SCSI is not technically defined as an interface; it is really an I/O bus in itself. SCSI technology supports peripheral devices such as hard drives, hard disk arrays, tape units, and CD-ROMs.
SCSI devices have unique SCSI ID numbers associated with them. These ID numbers are typically set with a jumper block on the SCSI device that includes three switches. Each switch setting represents a series of binary numbers that set a unique ID for each device. Each number represents the device’s position on the SCSI chain; these numbers are 0 through 7 for an SCSI-1 chain. The highest ID that can be assigned on a three-jumper SCSI-1 device is 7. A typical SCSI-1 chain can have up to eight devices (numbered 0 to 7) attached to it. An SCSI controller card is considered a device and uses SCSI ID number 7. That leaves seven SCSI IDs (0 to 6) available for peripheral devices.
SCSI priorities are applied from the highest ID number on the SCSI chain to the lowest number. For example, on an SCSI-1 chain, the controller with the unique SCSI ID of 7 has the highest priority. The priority decreases as you move down the SCSI chain to device 0. The same is true for the more popular SCSI-2 chain, which allows for 16 devices numbered 0 to 15. Device 15 would have the highest priority on the chain; device 0 would have the lowest priority. An SCSI chain must be terminated at both ends. Most SCSI devices come with a built-in terminator (terminator is another word for resistor). A terminator absorbs a signal so that the signal is not sent back to where it came from, causing a signal collision to occur. If you have an SCSI chain with a hard drive and a CD-ROM, you will need to terminate both ends of the SCSI chain for proper signal transmission to occur. In this case, you would terminate the SCSI hard drive and the SCSI CD-ROM. There have been several improvements made to SCSI technology since its original implementation. The following list stresses the important facts in reference to SCSI advances.
SCSI TerminationBoth ends of an SCSI bus must be terminated. The use of terminators prevents a signal from becoming distorted and prevents reflection that can cause severe data errors. There are two distinct types of SCSI termination used for a single-ended SCSI bus. They are known as active termination and passive termination:
If you are interested in learning more details regarding SCSI and SCSI termination, it is suggested that you visit the STA (SCSI Trade Association) Web site at: http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html#top. High-Voltage Differential (HVD)The original SCSI standard for SCSI interfaces was named single-ended (SE) SCSI, or SCSI-1. This specification for SCSI devices, which used a 50-pin connector, proved very susceptible to noise and did not offer long SCSI cable lengths. The HVD SCSI specification was introduced to overcome the noise and short cable length issues present in the original (SE) SCSI specification. High-voltage differential is a method by which an SCSI interface places data signals on SCSI cable. HVD SCSI interfaces utilize dual lines for each SCSI data signal. HVD SCSI is less susceptible to noise than SE and has a maximum cable length of 25 meters (approximately 82 feet). HVD SCSI interfaces can provide 20Mbps data transfer rates for narrow SCSI devices and 40Mbps transfers for wide SCSI. HVD SCSI uses +5V logic and terminators that run on 5V DC power. Low-Voltage Differential (LVD)Low-voltage differential is the newer data transmission standard for SCSI devices. LVD uses much less power than HVD and is less expensive. It is backward compatible with earlier single-ended SCSI (SCSI-1 and SCSI-2) and can automatically sense which type of SCSI you have. In other words, when your device is first powered up, LVD can distinguish whether your SCSI device is LVD compatible or single-ended. This auto-sensing LVD feature is called multimode operation. LVD device standards are defined (fall under) the Ultra 2 SCSI/SCSI-3 standards. Here are some of the benefits included with the LVD standard:
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A typical IDE/ATA interface supports two devices per motherboard controller. Most systems today have two separate motherboard controllers, allowing for a total of four devices to be attached. An EIDE interface can support up to four devices per controller, for a total of eight devices. EIDE is the same as ATA-2. ATA-2 is an improvement on IDE/ATA that also allows for up to four devices per controller, which equates to eight total devices. For the purposes of the A+ Core Hardware exam, we will focus on the traditional IDE/ATA standard interface that allows for two devices to be attached to each of the two motherboard controllers. This allows us to have a total of four devices—for example, two hard drives, a CD-ROM, and a tape drive unit. IDE hard drives, CD-ROMs, floppy drives, and other storage devices have jumper settings that determine the role they will play on an IDE interface. A jumper is a plastic and metal clip that is placed on two or more pins. These pins protrude from a device or a motherboard to close a circuit. With these jumpers, you can set the hard drive to be a master or slave drive, or choose cable-select settings.
A motherboard typically has a built-in primary and secondary controller (interface). A ribbon cable with a red stripe that represents pin 1 connects the hard drive and an optional device, such as a second hard drive or CD-ROM, to the motherboard’s primary IDE controller. Your primary master hard drive should be attached to the connector at the far end of the ribbon cable. When connecting the data cable to the hard drive, make sure that you match pin 1 on the adapter to pin 1 on the hard drive. The slave device should be connected to the middle connector. And finally, attach the other end of the data cable to the motherboard’s controller, verifying again that pin 1 on the cable matches pin 1 on the controller. The secondary controller can be used to connect two more devices to the motherboard. If you are only using the primary controller to connect devices, you can disable the secondary controller in the BIOS to free up IRQ 15 for other peripheral devices. The first device attached to the secondary controller is known as the secondary master. The second device attached is called the secondary slave.
If you are installing two new hard drives on the same IDE channel, you need to configure one to be the master drive and one to be the slave drive. If you reboot and the slave drive is not recognized by the system BIOS, you should test the slave drive by configuring it to be the master drive, remove the original master, and reboot the system. This will tell you if you have an incompatible or bad drive.
Following are the basic steps to installing a hard drive:
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Although the A+ Core exam is not likely to nail you with high-level questions regarding the various types of RAID (Redundant Array of Independent Disks) implementations, it is important for you to understand the basic implementations of RAID. Besides, anyone pursuing a career in the computing industry needs to understand fault-tolerance basics and RAID. RAID is one of the most popular means of providing fault-tolerant systems in use today. Through a process known as disk or “data” striping, RAID divides data into separate units and distributes the data across two or more hard disks. There are many variations of RAID available; the most popular are:
With all that being said about RAID, it is important that you know that RAID requires fast controllers/interfaces to be effective. All that reading and writing to multiple hard disks can quickly hamper a workstation’s or server’s ability to properly store and process data. Page 11
Optical storage devices and the usefulness of optical storage media, such as the Compact Disk Read-Only-Memory (CD-ROM), Compact Disk Recordable (CD-R), Compact Disk Rewritable (CD-RW), and Digital Versatile Disk (DVD), have taken the computer industry by storm. Optical media were originally intended as a replacement for recordable cassette tapes in the music industry; but as we know, optical media offer many advantages to the data storage world and have put the beloved 1.44MB floppy disk to shame. Although optical storage devices have a much slower access time than hard drive technologies, they offer many benefits. We can store books, music, pictures, and files on optical storage media. We can watch movies with DVD technology. The possibilities are almost endless, at least until the next form of storage media comes around. CD-ROMA CD-ROM is an optical storage disk capable of storing large amounts of data. A typical CD-ROM can hold 600MB to 800MB of information. This is equal to the storage capacity of about 700 1.44MB floppy disks. CD-ROMs are well suited for storing graphics files, movies, and music. A CD-ROM is typically written to, or ‘burned,’ once with information provided by the manufacturers of the CD-ROM. Optical media such as CD-ROMs have information burned into them by a laser beam. Actually, the term burned is used quite loosely here. For information to be written to a CD-ROM, the actual process involves changing the reflective properties of an organic dye that covers a CD-ROM by using a laser. The data can only be written to a disk one time. Reading the data on a CD-ROM requires the use of a CD-ROM device or player. CD-ROM players and writers can be installed internally or connected externally to a computer system. Most computers today come with an internal CD-ROM player installed. An internal CD-ROM device is typically installed as a slave device on either the primary or secondary IDE controller. An external CD-ROM device is connected to an SCSI, parallel, or USB port. MSCDEX.EXE (Microsoft CD-ROM Extension) is a file that contains a 16-bit software driver, which enables older operating systems, such as DOS and Windows 3x, to interact with and control CD-ROM players. MSCDEX was later replaced in Windows 95 by the 32-bit CD-ROM File System (CDFS), which offered better performance. CD-RA CD-R is an optical form of media that allows information to be written to the CD-ROM one time and read many times by the end user. It is sometimes referred to as Write-Once, Read-Many (WORM). To create CD-ROMs using CD-R technology, you need a compact-disk recordable drive and a CD-R software program installed in your system. CD-R technology is excellent for storing personal data and providing data backup capabilities. When purchasing such a unit and software, make sure that it has the capabilities for multisession recording. This is the ability to add files to a section of the CD-ROM that has not yet been written to. CD-R technology has become more affordable and is now commonplace. CD-RWCD-RW is the most popular CD technology at the present time. A CD-RW disk, with the use of a CD-ROM writing device, allows you to write information to the entire disk many times (approximately 25 times). CD-RW disks are more expensive than CD-R, but are well worth the price for the capabilities they offer. CD-RW technology will most likely be replaced by DVD technology when DVD storage advances become somewhat affordable. DVDDVD is quickly becoming the optical player and storage technology of choice. It has the capability to store up to 17GB of data, which is many times that of a CD-ROM, and can support several full-length motion pictures on one disk. DVD uses Motion Pictures Expert Group (MPEG) compression standards to provide its tremendous storage capabilities. Another great feature of DVD technology is that it is backward compatible with CD-R and CD-RW. This means that DVD can read CD-ROMs that you have created with CD-R or CD-RW technology. Several types of DVD technology are available today:
Test-related Tips For Optical Devices
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SuperDisks and Zip drives are used to store substantial amounts of information, which can help you free up hard disk space. They are an excellent portable storage alternative when you need more storage capability than a 1.44MB floppy can provide. The average SuperDisk can store 120MB of data, while remaining compatible with the average 1.44MB floppy disk. SuperDrive technology supports IDE, PCMCIA, USB, and parallel connectivity. Zip disks resemble floppy disks, but are about twice as thick. Zip disks can store either 100MB or 250MB, which is convenient for storing graphics or any other large files or programs for archival purposes, as well as for exchanging large amounts of information. Zip drive technology supports a parallel or SCSI connection. The Zip drive can be external or internal to the system unit. Page 13
This chapter covered very important material in relation to the current A+ Core Hardware exam and its heavy focus on storage devices and their interfaces. We covered the installation, configuration, and troubleshooting of the major storage devices and their components. There are many Internet sites available that go into far more detail on storage device engineering than is required for the goal and scope of this book. In order to be a proficient computer technician, you need hands-on practice installing and troubleshooting storage devices and computer-related equipment. Page 14
Answers
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http://www4.tomshardware.com/storage/20020812/. This Tom’s Guides Publishing site has an excellent description of Serial ATA. http://www.serialata.org/. This site is home of the Serial ATA Working Group. Serial ATA interface standards information is available at this site. http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html#top. This SCSI Trade Association Web site has an easy-to-understand paper regarding SCSI and SCSI termination. Page 16
Computing systems and other electronic devices use cables, connectors, and ports as a means to connect to and communicate with other devices. A cable is used to connect two devices. On each end of a cable is a connector; connectors are characterized as male or female. A cable’s male connector plugs into a female port, which may reside on a computer system or peripheral device. A female connector is connected to a male port, which may also be located on a system or peripheral device. Ports can be classified as internal or external to a system. Internal ports reside inside the system unit and connect components and devices directly to the motherboard. External ports are an extension of the motherboard or a peripheral device’s circuit board that protrudes from the system or device. A port on the back of a system unit is often referred to as a connector. It is important for the purposes of the test that you realize the term port can be used interchangeably with the term connector. As you go through this chapter, you will be introduced to some of the finer details related to cables and connectors. It is important to keep in mind that the exam will focus on the DB 25-pin and 36-pin Centronics D-shell parallel connector, 9-pin serial (COM) connector, DB 15-pin video connector, game/MIDI port connector, and 50-pin SCSI cable connector. EXTERNAL PORTSOn the back of a computer system you will find ports that are an extension of the motherboard’s form factor. You may find port extensions for devices such as NICs, AGP cards, modems, or sound cards. The expansion cards that these ports are attached to are inserted into the motherboard’s form factor. Most motherboards today are based on the ATX form factor, as described in Chapter 15, and include external connections for a parallel port, two serial ports, USB or FireWire (IEEE 1394) ports, a game controller port with microphone and speaker jacks, and a video port. Figure 21.1 shows the external ports associated with the ATX form factor. Pay special attention to the keyboard and mouse PS/2 connectors; the exam may focus on your ability to identify these in a graphic. The central focus of this chapter is these ports and the connectors associated with them. Before we continue with the fine details of ports and connectors, it is important to understand the transmission methods that many devices are capable of using. Page 17
Most peripheral devices, such as printers, scanners, and modems, utilize asynchronous transmission methods. With asynchronous transmission, data is not synchronized. Unlike synchronous transmission, data is not sent as a steady stream in a predetermined fashion. Instead, a start bit and a stop bit are placed between each piece, or ‘packet’ of information. Asynchronous transmission methods are typically used for devices attached to parallel or serial ports. Unlike asynchronous transmissions, synchronous transmissions are steady streams of data that are predetermined by a clock or counter. The CPU communicates with internal devices synchronously, basing the transmission of data and instructions on its own internal clock. Transmission ModesWhen two devices connect to each other, they establish and utilize a transmission mode. The transmission mode established between the two devices depends on the technology and configuration of the devices. Three general transmission modes are available that determine whether the transmission of data between two devices will occur only one way, one way at a time, or both ways at the same time. These transmission modes are simplex, half-duplex, and full-duplex.
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A parallel port, otherwise referred to as LPT1 or LPT2, is an external interface associated with the IEEE 1284 standard that is used to connect a computer to peripheral devices such as printers, CD-ROM players, scanners, or tape unit devices. Figure 21.1 shows a standard parallel port on the back of a system unit. A parallel port uses parallel transmission methods to transmit or send data one byte at a time to a peripheral device. A parallel cable has eight internal wires, and each wire is capable of sending one bit of information at a time. (Remember, there are eight bits in one byte.) Information is transmitted eight bits across all at once, for a total of one byte, in only one direction at a time using parallel transmission. It is important to note for the core exam that parallel transmission methods are faster than serial transmissions. Serial transmission methods will be discussed shortly. A parallel port on the back of a computer system is a female DB-25 connector that accepts a DB 25-pin male connector on one end of a parallel cable. The other end of a parallel cable has a 36-pin male Centronics D-shell connector that connects to a Centronics connector located on the back of a printer or device. Figure 21.2 shows the connectors on both ends of a typical parallel printer cable. Printer and scanner Centronics connectors typically use two clips to secure the connector to the port located on the back of the device. In addition, it is important to note that a parallel cable can also be used to connect or network two computers together. To ensure that the signals traveling down a parallel wire do not become distorted, the length of a parallel cable should not exceed 10 feet. Remember for the core exam that parallel transmission occurs 1 byte at a time. The newest addition to the IEEE 1284 standard for bidirectional communications and printing is the Type C-Mini 36-pin parallel connector. Also known as “Half Pitch Centronics 36 connectors,” these compact-size parallel connectors are often used with laptops and some newer printers. The Type C-Mini 36-pin parallel connector also provides support for Enhanced Parallel Port (EPP) applications.
In concluding our discussion of parallel cables and connectors, there are three types of parallel connections that you should be familiar with. They are:
The following RAM Electronics Industries, Inc. Web site offers some very good images of the three main parallel connector types as well as many of the other connectors mentioned in this chapter: http://www.ramelectronics.net/html/connecters.html. Page 19
Today’s computers typically come equipped with one or two RS232C-compliant serial ports that are also located on the back of a computer system. (Refer to Figure 21.1 for a standard serial port.) A serial port transmits data one bit at a time. To transmit a byte (eight bits) serially, eight separate bits are transmitted one at a time, one after another. For example, try to picture pouring eight marbles into a funnel all at the same time. Only one of the marbles can exit the funnel at a time. All the other marbles will follow the first marble until the funnel is empty. Serial transmission is much slower than any of the parallel transmission techniques. An operating system identifies serial ports in the BIOS setup program and references the serial ports as COM ports. The first serial port is referenced as COM1, the second serial port is referenced as COM2, and so on for COM3 and COM4. Serial ports can come in the form of a DB 9-pin or older style DB 25-pin male connector. Most systems today have one DB 9-pin (male) serial port that is used for a serial mouse or a communications device, such as a modem. Two basic serial cables are available that are used to connect a device to a serial port. The most common serial cable in use today has a DB 9-pin female adapter on one end of the cable that plugs into the DB 9-pin male serial port on the system unit. The other end of the cable has a DB 25-pin male connector, which is connected to a DB 25-pin female connector on the external device. An older-style serial cable is the DB 25-pin female to DB 25-pin male, which can connect two devices that have DB 25-pin serial ports. Yes, serial cables can network two computers together, but you should expect very slow transmission rates. Regardless of which serial cable is in use, the maximum length of a serial cable should not exceed 25 feet. Figure 21.3 displays the pin array configurations for male and female DB 9-pin and DB 25-pin serial connectors. Page 20
There are three main types of connectors used for keyboards and mice: the 5-pin Deutsche Industrie Norm (DIN) connector, the 6-pin mini-DIN (PS/2) connector, and USB mouse and keyboard connectors. Modern ATX form factor motherboards use PS/2 connectors for both the mouse and the keyboard. Older AT systems typically used a 5-pin DIN connector for the keyboard and a serial mouse. Figure 21.4 shows a 5-pin DIN and a 6-pin mini DIN (PS/2) connector. The 5-pin DIN keyboard connector was used in AT- and XT-class computers for a keyboard connection. It is much larger than a 6-pin mini-DIN connector and requires its own 5-pin port. The more popular 6-pin mini-DIN, otherwise known as a PS/2 connector, is the standard connector in use today for mice and keyboards. Nearly all systems today support PS/2 connections for mice and keyboards. (See Figure 21.1 for PS/2 mouse and keyboard ports on the back of a system using the ATX form factor.) Newer systems support USB mice and keyboard connections, which are very easy to install, support, and use. USB connectors will be discussed shortly. Older systems use a serial port DB-9 connector for what is commonly referred to as a bus mouse. A bus mouse requires the use of a free COM port and IRQ. Following are some very important facts to remember about mice and keyboards for the Core exam. The most important feature to look for when replacing a mouse or keyboard is the connectors associated with the device.
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All computer monitors have at least one thing in common: they all connect to a female DB 15-pin port on the back of a computer system. (Figure 21.1 shows a standard female DB 15-pin video port on the back of a system unit.) The DB 15-pin port may be attached directly to the motherboard, or it may be located on a video expansion card. The female DB 15-pin port has three rows of five pinholes that accept a male DB 15-pin connector, which is attached to the end of the monitor’s cable. Each of the 15 pins on the monitor’s DB-15 connector has a different pin assignment that carries out a specified video function related to power, color, or refresh rate. Many monitor-related problems can occur if one of these pins gets bent or broken. It is very important to take great care when connecting a DB 15-pin connector to a DB 15-pin port on the back of your system. Table 21.1 displays the functionality of each of the 15 pins on a DB 15-pin video connector.
The A+ Core exam is likely to present you with a question or diagram that tests your knowledge of the difference between a DB 15-pin video connector and a game/MIDI port, otherwise known as a joystick/MIDI port on a sound card. (See Figure 21.1 for the location of a game/MIDI port on a system unit.)
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As mentioned in Chapter 15, USB is a fairly new technology that supports mice, keyboards, scanners, printers, and digital cameras. USB is an external serial bus that supports both low-speed and high-speed devices, and offers data transfer rates of up to 12Mbps. Some of the advantages that USB technology has to offer are listed here.
USB devices can be ‘hot-swapped’ while an operating system is up and running. This means that you can attach or detach a USB mouse or keyboard when a computer is powered on.
There are two types of USB connectors in use today. Type A USB connectors have one of their connectors permanently attached to a device, such as a keyboard or a mouse. Type B USB connectors are totally detachable from both a device and a port. Figure 21.5 displays a typical Type A USB connector. One end of a Type A connector is actually built into the peripheral device. The other end of a Type A connector connects to a Type A port located on a host or USB hub. A Type A connector is flat and rectangular. Type B USB connectors are square and plug into a Type B USB port on both the device and the host. (See Figure 21.1 for the location of USB ports on a system unit.) USB 2.0The newest version of USB is called USB 2.0. USB 2.0 is sometimes referred to as Hi-Speed USB and supports transmission rates of up to 480Mbps. It is fully backward compatible with the early version of USB (USB 1.1). In a nutshell, USB version 2.0 uses the same exact connector cables and ports as the first version of USB. This USB specification was developed to meet the bandwidth-hungry needs of new devices and their technologies. Here are some USB tips for the exam:
The exam will ensure that you know that USB is RS232 compliant. In plain English (and on the CompTIA exam), this means that USB, RS232, and serial connections are all basically the same thing. For example, you might see something similar to this: “What is a very popular connection method for camcorders or digital cameras?” The possible choice of answers may include USB, RS232, or serial connection. You’d better choose them all! Page 23
FireWire is associated with Apple Computer Company’s original implementation of the IEEE standard 1394. The IEEE 1394 standard references high-speed serial transmissions of up to 400Mbps (in version 1394a) and 800Mbps (in version 1394b). FireWire is plug-and-play compatible and hot swappable; it also allows up to 63 devices to be connected to one port. A plug-and-play system will use the process known as “enumeration” to assign an address and auto-detect any FireWire-connected devices. A FireWire connector is somewhat similar in shape to a USB connector. The main difference is that a FireWire connector is larger and squarer than a typical USB connector. Figure 21.6 displays a FireWire connector. FireWire technology and other forms of the IEEE 1394 standard are expected to replace most serial and parallel connections in the future. For now, the IEEE 1394 standard is well suited for devices that require high speeds and large real-time throughput, such as video equipment. FireWire is much faster than USB, supporting data transfer rates of 100Mbps to 800Mbps. As a result, FireWire is also much more expensive than USB.
If you wish to learn more regarding FireWire, the following HowStuffWorks, Inc., Web site offers a superb explanation of FireWire basics: http://computer.howstuffworks.com/firewire1.htm. Page 24
As mentioned in Chapter 20, SCSI interfaces can be attached internally or externally to a computer system. For example, an SCSI hard drive can be attached to an internal SCSI controller on the motherboard. A device such as an SCSI printer or SCSI CD-ROM can be connected to an external SCSI controller card that extends out of the back of a computer. The devices that attach to SCSI controller cards have SCSI interfaces built onto them. There are internal and external SCSI connectors that reflect the SCSI standard being implemented on the device or controller. The most common SCSI interface connectors in use today are 50-pin and 68-pin SCSI internal and external SCSI connectors, as well as the 80-pin internal SCSI SCA connector. Devices such as printers and CD-ROMs utilize an SCSI 50-pin or 68-pin cable and connectors. SCSI SCA 80-pin connectors are used for hot-swappable hard drives, most commonly with internal RAID (Redundant Array of Independent Disks, or Redundant Array of Inexpensive Disks) configurations. The SCA SCSI adapter card includes a built-in power connection to support its special voltage requirements. Figure 21.7 shows the basic SCSI connectors and SCSI pin configurations. Remember, the exam will most likely focus on the 50-pin or 68-pin SCSI cable.
Here are several useful tips to remember about SCSI technology and interfaces:
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There are more than 2,500 types of cable in use for connecting computers and peripherals. The majority of computers today still use some type of wire or cable to transmit data from one system to another. There are three main types of network cables in use that you need to be familiar with for the Core exam: coaxial, twisted pair, and fiber optic. Each of these cable types has characteristics that set it apart from the others, such as cost, distance limitations, data transfer methods, data transfer rates, and installation methods used. The exam will focus on your ability to identify which technology is used by a certain cable category, and which cable medium should be used to connect two or more specific devices. Coaxial CableCoaxial cable is a type of copper cabling that is often times used for Ethernet local area network and cable TV connections. There are two common types of coaxial cable, they are thicknet and thinnet which are described next. ThicknetThicknet coaxial cable, also known as 10Base5, is approximately half an inch thick; it is a heavy type of cable with a copper core, which was used with early mainframe computers and early networks. Thicknet coaxial still exists, but it is very limited in its ability to achieve the high data transfer rates that are needed to support today’s bandwidth-hungry computers and applications. Thicknet coaxial cable has the ability to carry 10Mb (megabits) of data a total distance of 500 meters, or approximately 1,500 feet. Thus, the naming convention scheme of 10Base5 has been established for coaxial cable. In other words, 10Base5 means that 10Mb of information can travel over a baseband medium, or base, a total of 500 meters (the naming convention drops the last two zeros): 5 100 = 1,500 feet; the true measurement is closer to 1,640 feet. Thicknet coaxial cable was and sometimes still is used as a backbone connection that connects to a small thinnet cable by use of a vampire tap and an Attachment Unit Interface (AUI) connector. ThinnetThinnet coaxial cable, also known as 10Base2, is approximately a quarter-inch thick. It is a thinner, more flexible type of coaxial cable that is usually connected directly to an NIC with a BNC or BNC T-connector. Figure 21.8 displays a BNC and BNC T-connector. Thinnet is much easier to install and work with than thicknet, but thinnet only carries a data signal the distance of 185 meters, or approximately 607 feet. Both thicknet and thinnet coaxial can make up a network referred to as a bus network. (Bus networks are described in Chapter 22.) A bus network must be terminated at both ends of a cable, or the bus network will fail. Thus, thicknet and thinnet both require terminators at both cable ends. Twisted-Pair CableTwisted-Pair (TP) cable arose from the need to replace the distance and other limitations associated with coaxial-type cable. TP is referred to as 10BaseT. Once again, the 10 refers to the transmission rate of data, Base refers to a baseband media type, and the T refers to the twisted pair, or wiring twists in the cable itself. There are two types of twisted-pair wiring: Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP). Shielded Twisted PairSTP is basically the same type of wire as UTP, with the exception that STP uses a woven copper braided shielding and foil wrapping that protect the twisted wire pairs from outside interference, such as Electromagnetic Interference (EMI). This shielding makes an STP wire less susceptible to cross-talk from other wires. STP is more expensive than unshielded twisted pair, based on its extra protection and ability to transmit a data signal over a greater distance than UTP. Unshielded Twisted PairUTP is also a 10Mbps baseband cable. UTP, generally referred to as 10BaseT, is the most common type of Ethernet cable in use today and is found mostly in what is called a star typology network. (Star typology networks are discussed in detail in Chapter 22.) UTP in its simplest form is two insulated copper wires that can carry a data signal 100 meters, or approximately 328 feet. To keep wiring standards uniform, there are five categories of UTP wiring, as specified by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA):
To keep you sharp for the exam, here are the updated IEEE standard requirements for UTP cabling:
Twisted-Pair ConnectorsThere are two types of UTP connectors you need to know about for the test: RJ-11 connectors and RJ-45 connectors. An RJ-11 phone connector was used for early categories of UTP to connect a modem to a typical phone jack, or your phone to a phone jack. In technical circles, an RJ-11 wire is a simple phone wire that houses four wires or connections. See Figure 21.9 for an RJ-11 connector. An RJ-45 connector is the most common type of TP data cable connector in use. It houses eight wire traces. The RJ-45 connector on one end of a TP wire plugs into an NIC that is installed into a system. The RJ-45 connector on the other end of the TP cable plugs into a network hub, router, or RJ-45 wall jack. Figure 21.10 shows an RJ-45 connector. Crossover CableA crossover cable is a type of Ethernet TP cable that is commonly used to connect two computers in a peer-to-peer fashion. The crossover cable switches the transmit and receive lines of the cable, which allows two computers to communicate directly with each other without the use of a hub or router. If you want an inexpensive alternative to purchasing a hub, a crossover cable is the way to go to connect two computers. A null modem cable can also be used as a crossover cable to network two computers. A null modem cable is serial cable that is connected to the serial ports of two system units. Fiber-Optic CableFiber-optic cable, otherwise known as 10BaseFL, is the network wire of choice. It is capable of extremely fast transmission rates over long distances, without interference. A fiber-optic cable has a core that is composed of plastic or glass. A glass cladding or sheath covers the core. Finally, a Kevlar fiber jacket surrounds the entire wire. Data can be transmitted through a fiber-optic cable with a laser or LED at a rate of 2GBps or higher. The data signal on a fiber-optic wire can travel up to a distance of 100 kilometers (about 60 miles), depending on which technology is being implemented with the fiber and if a repeater is used. Fiber-optic cables use special ST- and SC-type connectors to attach to NICs and fiber-optic ports. These connectors are precisely crafted and specially designed to suit fiber-optic cable connection requirements. Fiber-optic cable needs great care and consideration when being installed. Specially trained, certified fiber installers are usually employed to carry out this task. Because of its high transmission speeds and specialized installation methods, fiber-optic technology is quite expensive. Next we will discuss the two fiber-optic cable mode technologies that you will need to be familiar with for the exam. Single-Mode (SM)Single-mode fiber optic, also referred to as monomode fiber, is a fiber technology meant for very long distance data transmissions. With single-mode fiber, a laser is used to generate a single pulse of light, or ‘mode of light,’ into the fiber media. This light is used as a data transmission carrier for a very long distance. Photodiodes are used to receive the transmission sent over the fiber-optic media. Multi-Mode (MM)Multi-mode fiber uses LEDs (Light Emitting Diodes) to generate signals of light into the core fibers for transmission over fiber media. This mode of fiber is designed to carry many light signal rays, or ‘modes,’ at the same time over a shorter distance than single mode. If the light rays, or ‘modes of light,’ have to travel too far with this mode, modal dispersion occurs and transmission fails. The core of the fiber media used with multi-mode is larger than with single mode; thus, the accepting photodiodes have a much larger circumference. Here are some key points:
Refer to Table 21.2 for a comparison chart of the major networking cables described in this chapter.
IDC (Insulation Displacement Connector)An insulation displacement connector is a connector that is used in various different types of network termination media or connection equipment. An IDC connector removes the insulation on a cable or wire when a connection is made. It works by piercing, or ‘crimping’ the insulation around the cable’s wires with a special tool called an IDC crimper. This technique is used to push or ‘force’ a single wire between two pieces of plastic, or ‘blades,’ that are part of a connector, such as an RJ-45 patch. An IDC assists with the process of timely termination and makes for an effective and reliable connection. Page 26
All those messy, dangling computer wires and connectors will soon be a thing of the past. Wireless technology has become very popular and affordable. In fact, you can set up a small wireless network at home for about $400. All you really need to set up a wireless network is a couple of transmitters, receivers, and a pair of wireless NICs. The operating system configuration for a wireless network is another story in itself. There are two main forms of wireless technologies in use for connecting computers together: Radio Frequency (RF) and Infrared (IR). Radio Frequency (RF)Many computer peripheral devices today utilize RF technology. With RF, a wireless mouse, keyboard, or modem can communicate with a host system as long as the distance between the peripheral and host does not exceed a specified distance. RF devices use transmitters, receivers, or transceivers (or a combination of these devices) to communicate back and forth. A typical RF mouse or keyboard transmits data through a built-in transmitter to a waiting receiver, which is attached to a system unit through a PS/2 or serial connection. RF devices are designed to meet the IEEE 802.11 standards that apply to wireless networking. Infrared (IR)Infrared transmission is a wireless form of transmission that also uses a transmitter and receiver. Instead of sending information with radio signals, however, infrared uses a beam of light that is not visible to the human eye to transmit data between two devices. Line-of-sight is a very popular type of infrared technology used to connect wireless devices, such as a mouse or keyboard, to a host system. The Infrared Data Association (IRDA) is the organization that is responsible for infrared transmission standards. Infrared technology has become very popular with laptop computers, PDAs, and digital cameras. With the infrared IRDA Standard 1.1, the maximum transmission rate is 4Mbps with a data size of 2048 bytes. Some of the common uses available for infrared transmission are these:
The majority of infrared transmissions occur between two computers or a single computer and an infrared-enabled device, such as a printer or PDA. The sending host or device uses an infrared transmitter or ‘emitter,’ which sends pulses of infrared light to the receiving host or device that accepts the pulses with an infrared receiver. In order for the transmission of this signal to occur, there must be a direct line of sight between communicating systems or devices, as well as a protocol and a computer name resolution. Infrared was originally designed for point-to-point bidirectional transmissions via an RS232C serial port. Today, most modern systems come equipped with an IRDA-standard port that can interface directly with an IR transmitter/receiver. IR connections can also be made through the use of a parallel or USB port. In conclusion to our infrared discussion, keep in mind that IR is sometimes called the “one-to-one” technology. You can only send to or receive from one device at a time. In other words, while you are transmitting or receiving information between your desktop computer and your PDA, you cannot transmit or receive data from your laptop and at the same time use infrared. Popular operating systems such as Microsoft Windows 95, 98, NT, 2000, XP and Windows Me offer support for adding IR devices. Early versions of Windows 95 required a special IRDA Software Patch that could be downloaded from Microsoft.com to enable IR support. In order for your system to use IR, support must be enabled in your system’s BIOS. Wireless Networking And SecurityWireless transmission is defined as the sending of signals over electromagnetic ‘radio’ waves. Wireless networks have become very widespread. In some cases, wireless networks have replaced the need for tradition wiring. But in larger networks, wireless technology is typically used as an extension or addition to a wired network. Wireless networks offer the ability for computing in places that would be otherwise hard to reach with a wire or cable. The use of wireless technology has been widely accepted by the military, hospitals, businesses, cell-phone companies, Global Positioning System (GPS) customers, museums, and home users alike. The IEEE has developed standards for wireless technologies. These standards are a set of rules that provide a sort of instruction map of guidelines for technology developers to follow when creating new technologies or adding to existing technologies. The IEEE standards that apply to wireless networking are: 802.11, 802.11a, 802.11b, and 802.11g. In its simplest of forms, a wireless network, or WLAN (Wireless Local Area Network), is displayed connected to a ‘wired’ LAN in Figure 21.11. Basic wirelesses networks typically have a wireless client, an authentication server, or ‘host,’ and an access point. The need to secure the use of wireless technologies and remote wireless user access has become paramount. Not too long ago, wireless connections were thought to be somewhat secure. Recently, these thoughts have changes, based on security holes found in the technology. Next we will discuss 802.1X standards and basic wireless protocols. 802.1XThe use and support of wireless networking, equipment, security, and protocols are on the rise. Although the fine details regarding 802.1X will most likely not be addressed on the exam, the following information will give you a very good understanding of wireless concepts. 802.1X is an IEEE standard for wireless connectivity that uses port-based access control. It falls under the influence of the initial IEEE standard 802.11 for WLANs. The IEEE and the standards that apply to networking technologies in general are explained in Chapter 22. In this chapter, we will discuss all of the IEEE 802.11 standards for wireless networking. The 802.1X standard is designed to provide a better framework that supports improved security for users of wireless networks by the implementation of centralized authentication. Standard 802.1X uses the Extensible Authentication Protocol (EAP), which enables the technology to work with wireless, Ethernet, and Token Ring networks. With 802.1X authentication, a wireless client who wishes to connect to and be authenticated on the network is called a supplicant. The supplicant must first request access from an access point, which is also known as an authenticator. If the access point detects the request for access from the supplicant, the access point will enable the supplicant’s port and only let 802.1X traffic be transmitted. This allows the client to transmit a start-up message, known as an EAP start message; the supplicant’s identity and credentials are then provided to the access point. The access point then transmits the information to an authentication server, which is typically a server that runs RADIUS (Remote Authentication Dial-In User Service). The authentication server can use various algorithms to eventually allow the user to be authenticated. Once the server authenticates the validity of the user, it will transmit either an acceptance or rejection acknowledgement of the client’s request to the access point. If the access point receives positive feedback from the RADIUS authentication server, the access point will enable or activate the supplicant’s port for normal network traffic. In simple terms, here is how 802.1X wireless authentication works. See Figure 21.12 for a visual regarding 802.1X authentication. To best understand this process, match the following descriptions with their corresponding numeric values in Figure 21.12:
The 802.1X standard is fairly new and it is not likely that CompTIA will target it extensively on the exam. However, you should be aware of the basics concepts. Microsoft does a great job explaining this technology. If you are interested in learning more about 802.1X you may find the following site very informative: http://www.microsoft.com/windowsxp/pro/techinfo/planning/wirelesslan/solutions.asp. WAPWAP (Wireless Application Protocol) is a wireless standard that applies to wireless communication protocols and devices. There are several standards that are used by various wireless device service manufacturers. WAP is positioned to allow interoperability between them. WAP has its own built-in security. It uses WTLS (Wireless Transport Layer Security), which uses secure certificates and a client/server verification/authentication process. WEPWEP (Wired Equivalent Privacy) is wireless security protocol specified under the IEEE 802.11b. WEP is intended to provide a WLAN with a similar security level as the protection that can be found in traditional LANs. WEP attempts to secure the obvious security hole that exists between a wireless client and an access point by encrypting the data that is transmitted. Once the data has been safely transmitted, it is thought that conventional network security measures (e.g., VLANS, antivirus, tunneling, and authentication solutions) can be implemented for security purposes.
Wireless Access PointsWireless access points are used in WLANs as central points of communication between wireless users. They are sometimes referred to as transceivers because they have the ability to transmit and receive RF signals. They are the ‘hub’ of wireless networks. Access points can also serve as a connection point between wireless users and a wired LAN, as depicted in Figure 21.11. Access points allow wireless users to roam in a generally predefined area called a “cell.” This cell is actually the area in which the RF signals can be successfully transmitted from the access point to the roaming, or ‘wireless,’ user and back again. In a small business environment, this area is typically around 100 feet, depending upon many outside physical and electrical conditions. In many businesses today, it is very common to find multiple access points strategically positioned around the business environment. When a mobile user moves outside the transmission area of one particular cell, they enter another cell area without losing the RF signal to the entire WLAN. Much larger cell areas are used for broadcasting such things as cellular phone ‘wireless’ radio waves. These cell areas can be as small as a city block or carry radio waves several hundred miles. Wireless AntennasIn wireless networking, an antenna is used to propagate, or ‘radiate’ RF signals to wireless users and access points in a wireless network. There are various antennas for wireless networking, and each has its own physical characteristics and specialized features. The two main types of wireless antennas that we need to be concerned about are:
Ad-HocIf a wireless network is set up using a peer-to-peer mode where wireless stations communicate directly with each other without the use of an access point, the wireless network is said to be using ad-hoc mode. An ad-hoc mode is usually implemented for temporary wireless transmission purposes. Site SurveysBefore you install a wireless network solution into an existing building or between existing buildings (building to building), you should first have a professional site survey conducted by certified RF engineers. These engineers can properly recommend and assist you with an integration plan, as well as keep you in line with federal, state, and local regulations as they apply to wireless networks. With traditional network installations, it is much easier to plan out a network topology and possibly foresee obstacles that will need to be addressed. However, with wireless networks that implement the use of radio transmission techniques, it is very difficult to plan for and determine how a network will react to the surrounding conditions. Obstacles such as asbestos-lined walls, trees, and other physical impediments can severely impact the effectiveness of wireless communication. The interference with other RF bands in busy airways can severely hamper your performance and ability to communicate between access points. Certified site survey technicians can detect potential interference between RF bands with a tool called a spectrum analyzer. A good site survey should provide you with the most suitable wireless equipment options to integrate with your current topology and applications. It should also provide you with a wireless standard that is in line with your required transmission speeds and, ultimately, your budget.
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