A common bus on the motherboard provides a connection from all interface cards to the CPU. Typically, five slots are built onto the motherboard for adding I/O cards. IBM created this common interface bus so that other manufacturers could build interface cards that would plug into the IBM PC.
The original bus was created for the 8088 processor, so it was eight bits wide. As new processors with wider external data buses were developed, wider expansion slots were created to provide faster throughput between I/O devices and the newer processors.
Industry Standard Architecture Bus
Industry Standard Architecture Bus
The two different Industry Standard Architecture (ISA) bus configurations are the original 8-bit ISA bus and the 16-bit AT ISA bus (shown in the photo above). Both configurations were designed to run at 8.33 MHz, though most run at around 7 MHz. The 8-bit ISA bus provides 31 pairs of connectors that fit in one of several expansion slots on the motherboard, while 16-bit ISA expansion slots provide an additional 18 pair of connectors.
Extended ISA Bus
The Extended ISA (EISA) bus was developed in the late 1980s to provide a faster (12 MHz), 32-bit-wide configurable expansion bus. When an expansion card is installed in an EISA slot, a configuration utility is used to configure the card. To make any changes to an EISA card, you must run the configuration utility. The EISA bus socket has two levels and 97 connectors. Both 8-bit and 16-bit ISA cards can be plugged into an EISA bus socket.
Video Electronics Standards Association Local Bus
Video Electronics Standards Association Local Bus
The Video Electronics Standards Association (VESA) developed the VESA Local (VL) bus to provide a faster video interface that would support the Windows desktop graphical user interface (GUI).
The VL bus extended the data bus to 32 bits to support the newer 32-bit Intel 486 processors. Practically speaking, the VL bus has a top speed of 33 MHz. The VL bus provides support for burst mode and bus mastering, and it can perform 32-bit data transfers. In burst mode, a VL bus device can take control of the external bus for up to four cycles to pass 128 bits of data in a single burst.
Because the VL bus is an extension of the 16-bit ISA bus, both local bus cards and 8-bit and 16-bit ISA cards can be used in these slots. The VL bus is used only with the 486 processor.
Peripheral Component Interconnect Bus
Peripheral Component Interconnect Bus
The latest expansion bus is the Peripheral Component Interconnect (PCI) bus, designed by Intel. The PCI bus is the most widely used and accepted expansion bus used on PCs. PCI is known as a mezzanine bus because it operates between the expansion bus and the system bus. PCI runs on an expansion bus that is separate from the ISA bus. The PCI bus acts as a bus master and takes control of the external data bus, which is necessary to pass data more efficiently. The PCI bus also has enhanced burst capabilities that provide extremely high throughput to PCI interface cards.
The PCI bus is currently 32 bits wide, but PCI-2.1 promises to provide both a 32-bit and a 64-bit data bus to take advantage of the Pentium’s 64-bit external data bus.
PC Card (PCMCIA)
PC Card (PCMCIA)
The PC card, formerly known as a personal computer memory card international association (PCMCIA) card, provides expandability for notebook computers. The three thicknesses of PC cards designates their type.
Type I — 3.3 mm thick
Type II — 5 mm thick
Type III — 10.5 mm thick; used primarily for hard drives
Most notebooks have two PC card expansions slots. The photo above shows a PC color card compared to the standard interface card.
Important: The Type III PCMCIA is used primarily for hard drives. Pay close attention to the differences between the PC card types.
I/O CARDS
Input/Output (I/O) cards, also known as interface cards, let you add capabilities to a PC that are not provided by the core components. I/O cards are installed in expansion slots; the card must match the type of expansion slot.
When installing a new interface card, the card’s IRQ and I/O memory address must be configured. If the card can utilize a DMA channel, that must be configured also. Older interface cards, now known as “legacy” cards, had switch banks or jumpers that you used to configure these settings. Many newer cards have Plug-and-Play (PNP) capability, and the motherboard or operating system can automatically configure the settings for those cards. Card configuration will be covered in detail in Chapter 3.
Cables connect the various part of a PC. Flat, gray ribbon cables connect the hard drive and floppy drive controller or interface to those devices. The ribbon cable has one lead that is painted red to indicate Pin 1.
Important: Ensure that the red band on the cable is connected to Pin I on the connector. Pin I is usually on the side closest to the power cable for that device.
Several other types of cables and connectors are available for connecting various devices to the computer. We cover cabling in greater detail in Chapter 3.
FLOPPY DRIVES
5.25-inch low density — stores 360K of data
5.25-inch high density — stores 1.2 MB of data
3.5-inch low density — stores 720K of data
3.5-inch high density — stores 1.44 MB of data
Floppy disks are a removable, permanent storage medium. Floppy drives work in much the same way as a tape recorder. A disk coated with a magnetic medium is enclosed in a protective cover. When the disk is placed in a floppy drive, the heads in the drive are lowered and read the information stored on the magnetic medium.
Floppy disk drives are rated by their physical size and capacity. Media sizes for floppy disks are 3.5 inches and 5.25 inches. The storage capacity of each of the sizes is listed above.
Note: A 3.5-inch,2.88 MB high-density standard was introduced but did not catch on with the industry. However, you can still purchase combination 1.44/2.88 drives. Floppies that store more than 100 MB of data are also available.
These devices are now so inexpensive that typically the only maintenance performed on floppy devices is cleaning the heads with a disk cleaning kit. If a problem still exists, the best solution is to replace the floppy drive.
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