Industry Standard Architecture

One 8-bit and five 16-bit ISA slots on a motherboard
8-bit XT, 16-bit ISA, EISA (top to bottom)
8-bit XT: Adlib FM Sound card
16-bit ISA: Madge 4/16 Mbps Token Ring NIC
16-bit ISA: Ethernet 10Base-5/2 NIC
8-bit XT: US Robotics 56k Modem

16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s.

- Industry Standard Architecture

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Peripheral Component Interconnect

Local computer bus for attaching hardware devices in a computer and is part of the PCI Local Bus standard.

Three 5-volt 32-bit PCI expansion slots on a motherboard (PC bracket on left side)
A typical 32-bit, 5 V-only PCI card, in this case, a SCSI adapter from Adaptec
A motherboard with two 32-bit PCI slots and two sizes of PCI Express slots
Diagram showing the different key positions for 32-bit and 64-bit PCI cards
A PCI-X Gigabit Ethernet expansion card with both 5 V and 3.3 V support notches, side B toward the camera
A semi-inserted PCI-X card in a 32-bit PCI slot, illustrating the need for the rightmost notch and the extra room on the motherboard to remain backward compatible
64-bit SCSI card working in a 32-bit PCI slot
A Mini PCI slot
Mini PCI Wi-Fi card Type IIIB
PCI-to-MiniPCI converter Type III
MiniPCI and MiniPCI Express cards in comparison
A PCI POST card that displays power-on self-test (POST) numbers during BIOS startup
A full-height bracket
A low profile one

The PCI Local Bus was first implemented in IBM PC compatibles, where it displaced the combination of several slow Industry Standard Architecture (ISA) slots and one fast VESA Local Bus (VLB) slot as the bus configuration.

IBM PC compatible

IBM PC compatible computers are similar to the original IBM PC, XT, and AT that are able to use the same software and expansion cards.

The Compaq Portable was one of the first nearly 100% IBM-compatible PCs.
The original IBM PC (Model 5150) motivated the production of clones during the early 1980s.
The DEC Rainbow 100 runs MS-DOS but is not compatible with the IBM PC.
MS-DOS version 1.12 for Compaq Personal Computers
The PowerPak 286, an IBM PC compatible computer running AutoCAD under MS-DOS.

It was later re-named the Industry Standard Architecture (ISA) bus, after the Extended Industry Standard Architecture bus open standard for IBM PC compatibles was announced in September 1988 by a consortium of PC clone vendors, led by Compaq and called the Gang of Nine, as an alternative to IBM's proprietary Micro Channel architecture (MCA) introduced in its PS/2 series.

Parallel ATA

Standard interface designed for IBM PC-compatible computers.

Two ATA motherboard sockets on the left, with an ATA connector on the right.
Two ATA motherboard sockets on the left, with an ATA connector on the right.
Example of a 1992 80386 PC motherboard with nothing built in other than memory, keyboard, processor, cache, realtime clock, and slots. Such basic motherboards could have been outfitted with either the ST-506 or ATA interface, but usually not both. A single 2-drive ATA interface and a floppy interface was added to this system via the 16-bit ISA card.
An Oak Technology Mozart 16 16-bit ISA sound card, from when the CDROM drive interface had not yet been standardized. This card offers four separate interface connectors for IDE, Panasonic, Mitsumi, and Sony CDROM drives, but only one connector could be used since they all shared the same interface wiring.
A SoundBlaster 32 16-bit ISA sound card, from after connector standardization had occurred, with an IDE interface for the CDROM drive.
80 pin parallel ATA interface on a 1.8" hard disk
Comparison between ATA cables: 40-conductor ribbon cable (top), and 80-conductor ribbon cable (bottom). In both cases, a 40-pin female connector is used.
Differences between connectors
PATA to USB Adapter. It is mounted on the rear of a DVD-RW optical drive inside an external case
Compact flash is a miniature ATA interface, slightly modified to be able to also supply power to the CF device.

The standard was originally conceived as the "AT Bus Attachment," officially called "AT Attachment" and abbreviated "ATA" because its primary feature was a direct connection to the 16-bit ISA bus introduced with the IBM PC/AT.

IBM Personal Computer/AT

Released in 1984 as the fourth model in the IBM Personal Computer line, following the IBM PC/XT and its IBM Portable PC variant.

The AT bus became the de facto "ISA" (Industry Standard Architecture), while PC XT slots were retroactively named "8-bit ISA".

Micro Channel architecture

Proprietary 16- or 32-bit parallel computer bus introduced by IBM in 1987 which was used on PS/2 and other computers until the mid-1990s.

IBM XGA-2 32-bit Graphics Card
CHIPS P82C612 in a PLCC package
IBM 83X9648 16-bit Network Interface Card
Roland MPU-IMC; second revision with IRQ jumpers
ChipChat 16 with software-controlled IRQ selection

In IBM products, it superseded the ISA bus and was itself subsequently superseded by the PCI bus architecture.

IBM Personal Computer

First microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard.

IBM Personal Computer with keyboard and monitor
IBM Personal Computer with keyboard and monitor
Internal view of a PC compatible computer, showing components and layout.
Original IBM Personal Computer motherboard
IBM PC with MDA monitor
IBM Model F keyboard
IBM Personal Computer with IBM CGA monitor (model 5153), IBM PC keyboard, IBM 5152 printer and paper stand. (1988)
The back of a PC, showing the five expansion slots
PC DOS 3.30 running on an IBM PC
Digital Research CP/M-86 Version 1.0 for the IBM PC

IBM referred to these as "I/O slots," but after the expansion of the PC clone industry they became retroactively known as the ISA bus.

Plug and play

One with a specification that facilitates the discovery of a hardware component in a system without the need for physical device configuration or user intervention in resolving resource conflicts.

A third-party serial interface card for the Apple II that required cutting and soldering to reconfigure. The user would cut the wire traces between the thinly connected ⧓ triangles at X1 and X3 and solder across the unconnected ◀▶ pads at X2 and X4 located at the center of the card. Once done, reverting the modification was more difficult.
A NuBus expansion card without jumpers or DIP switches
An MCA expansion card without jumpers or DIP switches
An example of an ISA interface card with extremely limited interrupt selection options, a common problem on PC ISA interfaces. Kouwell KW-524J dual serial, dual parallel port, 8-bit ISA, manufactured in 1992: * Serial 1: IRQ 3/4/9 * Serial 2: IRQ 3/4/9 * Parallel 1: IRQ 5/7 * Parallel 2: IRQ 5/7 (There is no technical reason why 3,4,5,7,9 cannot all be selectable choices for each port.)

Initially all expansion cards for the IBM PC required physical selection of I/O configuration on the board with jumper straps or DIP switches, but increasingly ISA bus devices were arranged for software configuration.

Extended Industry Standard Architecture

Bus standard for IBM PC compatible computers.

Three EISA slots
SCSI controller (Adaptec AHA-1740)
Fast SCSI RAID controller (DPT PM2022)
ELSA Winner 1000 Video card for ISA and EISA

In comparison with the AT bus, which the Gang of Nine retroactively renamed to the ISA bus to avoid infringing IBM's trademark on its PC/AT computer, EISA is extended to 32 bits and allows more than one CPU to share the bus.

Direct memory access

Feature of computer systems and allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU).

Motherboard of a NeXTcube computer (1990). The two large integrated circuits below the middle of the image are the DMA controller (l.) and - unusual - an extra dedicated DMA controller (r.) for the magneto-optical disc used instead of a hard disk drive in the first series of this computer model.
Cache incoherence due to DMA

With the IBM PC/AT, the enhanced AT Bus (more familiarly retronymed as the ISA, or "Industry Standard Architecture") added a second 8237 DMA controller to provide three additional, and as highlighted by resource clashes with the XT's additional expandability over the original PC, much-needed channels (5–7; channel 4 is used as a cascade to the first 8237).


American information technology company founded in 1982 that developed, sold, and supported computers and related products and services.

First Compaq logo, used until 1993
Compaq Portable
Compaq Portable 386 BIOS
Aerial map of the Compaq headquarters, now the HP USA campus in unincorporated Harris County, Texas
Former Compaq headquarters, now the Hewlett-Packard United States campus
Post merger logo for Compaq products.
An example of a HP Compaq.

Although Compaq had become successful by being 100 percent IBM-compatible, it decided to continue with the original AT bus—which it renamed ISA—instead of licensing IBM's MCA.