Three 5-volt 32-bit PCI expansion slots on a motherboard (PC bracket on left side)
One 8-bit and five 16-bit ISA slots on a motherboard
A typical 32-bit, 5 V-only PCI card, in this case, a SCSI adapter from Adaptec
8-bit XT, 16-bit ISA, EISA (top to bottom)
A motherboard with two 32-bit PCI slots and two sizes of PCI Express slots
8-bit XT: Adlib FM Sound card
Diagram showing the different key positions for 32-bit and 64-bit PCI cards
16-bit ISA: Madge 4/16 Mbps Token Ring NIC
A PCI-X Gigabit Ethernet expansion card with both 5 V and 3.3 V support notches, side B toward the camera
16-bit ISA: Ethernet 10Base-5/2 NIC
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
8-bit XT: US Robotics 56k Modem
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.

- Peripheral Component Interconnect

Later buses such as VESA Local Bus and PCI were used instead, often along with ISA slots on the same mainboard.

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

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IBM XGA-2 32-bit Graphics Card

Micro Channel architecture

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In IBM products, it superseded the ISA bus and was itself subsequently superseded by the PCI bus architecture.

Multi-I/O-Controller with 1×IDE/SCSI-2/FDD/parallel/2×RS232/Game

VESA Local Bus

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Short-lived expansion bus introduced during the i486 generation of x86 IBM-compatible personal computers.

Short-lived expansion bus introduced during the i486 generation of x86 IBM-compatible personal computers.

Multi-I/O-Controller with 1×IDE/SCSI-2/FDD/parallel/2×RS232/Game
An ATI MACH64 SVGA VLB graphics card
Computer motherboard with 7 ISA slots of various feature levels. The top three are 16-bit ISA. The middle three are VLB; 16-bit ISA with the added slot (leftmost brown sections). The bottom (shorter) slot is 8-bit ISA. A card installed in this motherboard would have its mounting bracket on the right, which normally would be the "back" of the computer case.
"VIP" motherboard GA486IM from Gigabyte Technology
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Created by VESA (Video Electronics Standards Association), the VESA Local Bus worked alongside the then-dominant ISA bus to provide a standardized high-speed conduit intended primarily to accelerate video (graphics) operations.

It would be superseded by Peripheral Component Interconnect(PCI), starting at speeds of 133 MB/s (32-bit at 33 MHz in the standard configuration)

Three EISA slots

Extended Industry Standard Architecture

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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
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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.

By the time there was a strong market need for a bus of these speeds and capabilities for desktop computers, the VESA Local Bus and later PCI filled this niche, and EISA vanished into obscurity.

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

IBM PC compatible

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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.

Soon after the industry adopted new bus standards in a similar, cooperative way: the VESA Local Bus (VLB), Peripheral Component Interconnect (PCI) and the Accelerated Graphics Port (AGP).

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)

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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

In these cases, expansion buses are entirely separate and no longer share any architecture with their host CPU (and may in fact support many different CPUs, as is the case with PCI).

Industry Standard Architecture or ISA

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

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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).

Particularly, the advent of the 80386 processor in 1985 and its capacity for 32-bit transfers (although great improvements in the efficiency of address calculation and block memory moves in Intel CPUs after the 80186 meant that PIO transfers even by the 16-bit-bus 286 and 386SX could still easily outstrip the 8237), as well as the development of further evolutions to (EISA) or replacements for (MCA, VLB and PCI) the "ISA" bus with their own much higher-performance DMA subsystems (up to a maximum of 33 MB/s for EISA, 40 MB/s MCA, typically 133 MB/s VLB/PCI) made the original DMA controllers seem more of a performance millstone than a booster.

Two ATA motherboard sockets on the left, with an ATA connector on the right.

Parallel ATA

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Standard interface designed for IBM PC-compatible computers.

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.

For example, the maximum data transfer rate for conventional PCI bus is 133 MB/s, and this is shared among all active devices on the bus.