Input–Output Design and Organization - Fundamentals of Computer Organization and Architecture - page 181

8.6. INPUT-OUTPUT INTERFACES

An interface is a data path between two separate devices in a computer system. Inter-
face to buses can be classified based on the number of bits that are transmitted at a
given time to serial versus parallel ports. In a serial port, only 1 bit of data is trans-
ferred at a time. Mice and modems are usually connected to serial ports. A parallel
port allows more than 1 bit of data to be processed at once. Printers are the most
common peripheral devices connected to parallel ports. Table 8.4 shows a summary
of the variety of buses and interfaces used in personal computers.

TABLE 8.4 Descriptions of Buses and Interfaces Used in Personal Computers

Bus / Interface Description

PS / 2 A type of port (or interface) that can be used to connect mice and

keyboards to the computer. The PS / 2 port is sometimes called the
mouse port.

Industry standard
architecture (ISA)

ISA was originally an 8-bit bus and later expanded to a 16-bit bus in
1984. In 1993, Intel and Microsoft introduced a plug and play
ISA bus that allowed the computer to automatically detect and set
up computer ISA peripherals such as a modem or sound card.

Extended industry
standard
architecture
(EISA)

EISA is an enhanced form of ISA, which allows for 32-bit data
transfers, while maintaining support for 8- and 16-bit expansion
boards. However, its bus speed, like ISA, is only 8 MHz. EISA is
not widely used, due to its high cost and complicated nature.

Micro channel
architecture
(MCA)

MCA was introduced by IBM in 1987. It offered several additional
features over the ISA such as a 32-bit bus, automatically
configured cards and bus mastering for greater efficiency. It is
slightly superior to EISA, but not many expansion boards were
ever made to fit MCA specifications.

VESA (Video
electronics
standards
association) local
bus (VLB)

The VESA, a nonprofit organization founded by NEC, released the
VLB in 1992. It is a 32-bit bus that had direct access to the system
memory at the speed of the processor, commonly the 486 CPU
(33 / 40 MHz). VLB 2.0 was later released in 1994 and had a
64-bit bus and a bus speed of 50 MHz.

Peripheral
component
interconnect (PCI)

PCI was introduced by Intel in 1992, revised in 1993 to version 2.0,
and later revised in 1995 to PCI 2.1. It is a 32-bit bus that is also
available as a 64-bit bus today. Many modern expansion boards
are connected to PCI slots.

Advanced graphic
port (AGP)

AGP was introduced by Intel in 1997. AGP is a 32-bit bus designed for
the high demands of 3D graphics. AGP has a direct line to memory,
which allows 3D elements to be stored in the system memory
instead of the video memory. AGP is geared towards data-intensive
graphics cards, such as 3D accelerators; its design allows for data
throughput at rates of 266 MB / s.

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