Hard drives are faster, larger, and more reliable storage devices than floppy drives. A hard drive is not considered a removable medium, because you can’t take it out without dismantling the PC. Hard drives have changed since they were first introduced with the IBM-compatible PC. The standard hard drive of today can hold hundreds of times the data and retrieve that data many times more quickly than hard drives could 10 years ago.
The PC uses the hard drive as the primary storage device for the operating system, applications, and data. Typically, a hard drive failure is the most traumatic event that can occur on a PC. If the hard drive breaks and the data is not backed up, the data is lost forever.
The two most widely used hard drive technologies today are IDE and SCSI. Be sure to concentrate on IDE and SCSI, not the older specifications.
Modified Frequency Modulation
The Modified Frequency Modulation (MFM) drive used the earliest technology. Frequency Modulation (FM) encoding was used on the first floppy drives installed in PCs. MFM was designed to reduce the number of flux reversals used in the original FM encoding scheme, thereby allowing more data to be placed on the disk. Two cables connected the disk drive to the MFM hard drive controller — one cable was for control, the other was for data. MFM hard disk drives used 5.25-inch disk platters.
MFM technology is still used for floppy disk drives but not hard drives.
Run Length Limited
Run Length Limited (RLL) disk drives are no longer used in the industry, but the encoding method is. In fact, it’s the most widely used and popular encoding scheme for hard disks because it can store 50 percent more data on a disk than MFM encoding.
The RLL disk drive had the same outward appearance as the MFM drive, but the controller cards were typically smaller. RLL drives were also connected to the RLL controller card with two cables and used 5.25-inch disk platters.
Enhanced Small Device Interface
The Enhanced Small Device Interface (ESDI) was created by a consortium of drive manufacturers and provided increased reliability and much higher throughput of data over the previous controller standard. At the time ESDI drives and controllers were becoming popular, the IDE interface (discussed in more detail in a moment) was also introduced. Because the IDE interface cost less, it became the industry standard. Two cables connected the ESDI drive to the ESDI controller — one cable for control, the other for data.
Small Computer System Interface
The Small Computer System Interface (SCSI) is a system-level interface and was developed for minicomputers before PCs were introduced (see Figure 2.5).
Actually, SCSI controllers aren’t controllers but instead are buses that support up to eight devices (one of the devices is the host adapter or controller). Each device on the SCSI interface is assigned a SCSI ID, numbered from 0 through 7; the host adapter uses SCSI ID 7.
Important: Several different types of SCSI buses have been developed. These SCSI controllers allow more than seven devices to be connected to a single controller and provide some additional abilities.
The SCSI bus supports many different types of devices, including hard drives, tape backup units, scanners, CD-ROM drives, and printers. Internal SCSI devices are installed inside the computer case, while external SCSI devices connect to the PC via a cable that connects to the SCSI host adapter installed in the PC’s expansion bus.
The SCSI bus structure has two ends, with devices connected between them. On each end of the SCSI bus, you must install a terminator pack to help reduce the amount of noise on the bus cable. Therefore, a SCSI bus has two terminators, one on each end.
Important: A SCSI bus has two ends. Both ends must be terminated with a terminating resistor pack.
Several different “flavors” of SCSI buses are available, including
SCSI-1
SCSI-2, which can include
Fast SCSI
Wide SCSI
Command Queuing
High-density cable connectors
Active termination
SCSI-3, which is the standard in development now
For more information about SCSI standards and specifications, see the Adaptec Web site. Adaptec currently makes the most widely used and accepted SCSI host adapters in the PC industry.
Integrated Drive Electronics
Integrated Drive Electronics (IDE) is a general term for drives with built-in disk controllers, a popular term used for AT Attachment (ATA) disk drives, and an ANSI standard. The IDE hard drive is the most popular drive used on PCs because the price per megabyte of storage is much less than the price for SCSI storage.
The IDE drive connects to an interface card by one ribbon cable. Remember, the controller functionality is on the hard drive. The card in the expansion slot of the motherboard is an interface card, not a controller. This distinction may seem small, but it makes it possible to have an industry-standard interface card while allowing each drive manufacturer to create its own controller on the hard drive.
On a system with two IDE drives, one drive is called the master drive and the other is the slave drive. The controller portion of the slave drive is disabled, and the master drive controls both drives. Only two drives can be chained.
Note: IDE and EIDE devices have small jumpers that let you set one as the master and one as the slave on each chain.
Enhanced IDE
Enhanced IDE (EIDE) describes the ATA-2 extension of the original ATA (IDE) specification. EIDE provides these enhancements to the original ATA interface:
Faster data transfer — PIO transfer mode 3 and 4 are supported, providing transfer rates of 11.1 and 16.6 M/sec, respectively.
Increased maximum drive capacity — The size limit for original IDE hard drives was 504 MB. By using translation, IDE supports much larger hard drives. The following translation types are used.
Standard CHS (Cylinders, Heads, Sectors)
Extended CHS (Cylinders, Heads, Sectors)
LBA (Large Block Addressing)
Secondary two-device channel — A secondary hard drive connector can connect two more hard disks, bringing the total supported to four.
AT Attachment Packet Interface (ATAPI) — a specification that defines device-side characteristics for IDE-connected devices such as CD-ROMs and tape drives. Basically, ATAPI converts the SCSI command set into an IDE interface commands set.
Important: The EIDE standard supports hard drives larger than 504 MB, upto four hard drives, and a common ATAPI interface for tape drives and CD-ROMS.
VIDEO
Monochrome Display Adapter (MDA)
Color Graphics Adapter (CGA)
Enhanced Graphics Adapter (EGA)
Video Graphics Array (VGA)
Super VGA (SVGA)
Advanced Graphic Port (AGP)
The video subsystem for PCs has undergone dramatic changes since the introduction of the PC. Originally, text-based characters could be displayed in only one color on a monitor. The next stage provided four colors of text-based characters, followed by support for 16 colors and higher resolutions, and even limited support for graphic characters. At that point, the digital signal that was sent from the controller card to the monitor was changed to an analog signal created on the interface card and sent to a VGA monitor.
Table 2.2 shows the different video modes supported through SVGA support.
Since the introduction of the VGA monitor, the display resolution and the number of colors that can be displayed have increased dramatically, to resolutions greater than 1280 x 1024 pixels and more than 16 million possible colors. Because they aren’t used widely anymore, we do not discuss the older digital display modes. The CompTIA A+ Certification exam focuses on VGA and SVGA modes.
Video Graphics Array
The Video Graphics Array (VGA) interface card was the first card to provide an analog signal to the monitor. It also provided support for GUI operating systems. The highest resolution supported by VGA is 640 x 480 with 256 colors. The connector on the back of the interface card for MDA, CGA, and EGA (early modes not discussed) was a 9-pin, 2-row female socket. The VGA and SVGA interface cards use a 15-pin, 3-row female socket connector on the back of the interface card.
Super VGA
The Super Video Graphics Array (SVGA) card was developed to provide higher resolutions. Originally, SVGA cards provided 800 x 600 resolution with 256 colors but now can provide resolution greater than 1280 x 1024, with more than 16 million displayable colors. The SVGA cards and VGA cards use the same connector.
Many of today’s video cards come with 4 MB to 8 MB of RAM. Some of the more advanced cards have even more RAM and support higher resolutions and increased performance.
Advanced Graphic Port
The Advanced Graphic Port (AGP) video board is one of the newer PC video adapters on the market. This type of adapter provides enhanced 3-dimensional (3-D) video support and can communicate directly with the system’s RAM. Newer Pentium-based processor chips have built-in circuitry that provides more efficient communication with the video board, thus enabling much quicker, higher-speed 3-D graphics on PCs. The only AGP video boards available use the PCI bus structure and typically have 4 MB to 8 MB of RAM on board.
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