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
One 8-bit and five 16-bit ISA slots on a motherboard

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Alpha

Three 5-volt 32-bit PCI expansion slots on a motherboard (PC bracket on left side)

Peripheral Component Interconnect

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

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.

The Compaq Portable was one of the first nearly 100% IBM-compatible PCs.

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.

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.

IBM XGA-2 32-bit Graphics Card

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.

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 with keyboard and monitor

IBM Personal Computer

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

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.

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.

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".

Four PCI Express bus card slots (from top to 2nd bottom: ×4, ×16, ×1 and ×16), compared to a 32-bit conventional PCI bus card slot (very bottom)

Bus (computing)

Communication system that transfers data between components inside a computer, or between computers.

Communication system that transfers data between components inside a computer, or between computers.

Four PCI Express bus card slots (from top to 2nd bottom: ×4, ×16, ×1 and ×16), compared to a 32-bit conventional PCI bus card slot (very bottom)
Single system bus

Industry Standard Architecture or ISA

Three EISA slots

Extended Industry Standard Architecture

Bus standard for IBM PC compatible computers.

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
200px

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.

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.

Direct memory access

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

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).

A pair of AMD BIOS chips for a Dell 310 computer from the 1980s

BIOS

Firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup).

Firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup).

A pair of AMD BIOS chips for a Dell 310 computer from the 1980s
Boot process
BIOS chips in a Dell 310 that were updated by replacing the chips
Award BIOS setup utility on a standard PC
BIOS replacement kit for a Dell 310 from the late 1980s. Included are two chips, a plastic holder for the chips, and a chip puller.
American Megatrends BIOS 686. This BIOS chip is housed in a PLCC package in a socket.
Compaq Portable 386 BIOS
An American Megatrends BIOS showing an "Intel CPU uCode Loading Error" after a failed attempt to upload microcode patches into the CPU
A detached BIOS chip

Once the system is booted, hardware monitoring and computer fan control is normally done directly by the Hardware Monitor chip itself, which can be a separate chip, interfaced through I2C or SMBus, or come as a part of a Super I/O solution, interfaced through Industry Standard Architecture (ISA) or Low Pin Count (LPC).

Compaq

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

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.