Information Technology Reference
In-Depth Information
3.7
Summary of interface bus types
Devices connect to the microprocessor using a computer bus. The specification of this bus
defines the transfer speed between the microprocessor and the connected device. Peripherals
can connect to the computer using either an internal or an external interface. Table 3.3 and
Table 3.4 give some examples of typical PC interfaces.
Table 3.3
Internal PC busses
Bus
Description
Typical devices
connected
ISA
The ISA (International Standards Architecture) bus uses an inter-
face card which has two edge connectors (as one of the connec-
tors was used on the original PC bus). Typical ISA connections
are network interface adaptors, video camera interfaces and
sound cards. It can transfer up to 16 bits at a time, and uses a
fixed transfer rate of 8 MHz (8 000 000 transfers every second).
Max: 16 MB/s.
Network adaptor
Video camera adaptor
Sound card
PCI
The PCI (Peripheral Component Interconnection) bus is used
connect internal devices in the PC. Typically, modern PCs have
at least four PCI adaptors, which are used to connect to network
interface cards, graphics adaptors and sound cards. It can transfer
up to 32 bits at a time. Max: 132 MB/s (more typically, 66 MB/s).
Network adaptor
Video camera adaptor
Sound card
AGP
The AGP (Accelerated Graphics Port) bus is used solely to con-
nect to video cards. It uses a special connector, but builds on the
standard PCI bus. It is optimised so that it uses the main memory
of the computer, and does not depend on memory on the graphics
card. Max: 500 MB/s.
Graphics adaptor
IDE
The Integrated Drive Electronics (IDE) bus is used solely to con-
nect to either hard disk drives, or CD-ROM drives. There are two
IDE connections: IDE0 and IDE1. Up to two devices can connect
to each IDE connector, thus up to four disk drives can connect to
the IDE bus.
Max: 16.6 MB/s (IDE, Mode 4).
Hard disk drive
CD-ROM drive
The Personal Computer Memory Card International Association
(PCMCIA) interface allows small thin cards to be plugged into
laptop, notebook or palmtop computers. It was originally de-
signed for memory cards (Version 1.0) but has since been
adopted for many other types of adapters (Version 2.0), such as
fax/modems, sound-cards, local area network cards, CD-ROM
controllers, digital I/O cards, and so on. Most PCMCIA cards
comply with either PCMCIA Type II or Type III. Type I cards
are 3.3 mm thick, Type II take cards up to 5 mm thick, Type III
allows cards up to 10.5 mm thick. A new standard, Type IV,
takes cards which are greater than 10.5 mm. Type II interfaces
can accept Type I cards, Type III accept Types I and II and Type
IV interfaces accept Types I, II and III. It uses a 16-bit data trans-
fer.
Network adaptor
Modem adaptor
Sound card
CD-ROM drive
Memory upgrade
Hard disk drive
PCMCIA
 
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