Industry Standard Architecture (ISA) is the 16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s.

In 1988, the 32-bit EISA standard was proposed by the "Gang of Nine" group of PC-compatible manufacturers that included Compaq.

Compaq created the term Industry Standard Architecture (ISA) to replace PC compatible.

The 16-bit version was an upgrade for the motherboard buses of the Intel 80286 CPU (and expanded interrupt and DMA facilities) used in the IBM AT, with improved support for bus mastering.

ISA was also used in some non-IBM compatible machines such as Motorola 68k-based Apollo (68020) and Amiga 3000 (68030) workstations, the short-lived AT&T Hobbit and the later PowerPC-based BeBox.

However, MCA was also a closed standard whereas IBM had released full specifications and circuit schematics for ISA.

Computer manufacturers responded to MCA by developing the Extended Industry Standard Architecture (EISA) and the later VESA Local Bus (VLB).

Users frequently had to configure parameters when adding a new device, such as the IRQ line, I/O address, or DMA channel.

PCI slots were the first physically incompatible expansion ports to directly squeeze ISA off the motherboard.

Microsoft's PC-99 specification recommended that ISA slots be removed entirely, though the system architecture still required ISA to be present in some vestigial way internally to handle the floppy drive, serial ports, etc., which was why the software compatible LPC bus was created.

In late 2008, even floppy disk drives and serial ports were disappearing, and the extinction of vestigial ISA (by then the LPC bus) from chipsets was on the horizon.

This was at best awkward and at worst damaging to the motherboard, as ISA slots were not designed to support such heavy devices as HDDs.

ATA is basically a standardization of this arrangement plus a uniform command structure for software to interface with the HDC within the drive.

ATA has clear characteristics of 16-bit ISA, such as a 16-bit transfer size, signal timing in the PIO modes and the interrupt and DMA mechanisms.

Power lines included −5 V and ±12 V in order to directly support pMOS and enhancement mode nMOS circuits such as dynamic RAMs among other things.

The XT bus architecture uses a single Intel 8259 PIC, giving eight vectorized and prioritized interrupt lines.

The 16-bit AT bus slot originally used two standard edge connector sockets in early IBM PC/AT machines.

However, with the popularity of the AT architecture and the 16-bit ISA bus, manufacturers introduced specialized 98-pin connectors that integrated the two sockets into one unit.

In 2008, IEI Technologies released a modern motherboard for Intel Core 2 Duo processors which, in addition to other special I/O features, is equipped with two ISA slots.

[7] Similarly, ADEK Industrial Computers released a modern motherboard in early 2013 for Intel Core i3/i5/i7 processors, which contains one (non-DMA) ISA slot.

In addition to the physical interface channel, ATA goes beyond and far outside the scope of ISA by also specifying a set of physical device registers to be implemented on every ATA (IDE) drive and a full set of protocols and device commands for controlling fixed disk drives using these registers.

The earliest versions of the ATA standard featured a few simple protocols and a basic command set comparable to the command sets of MFM and RLL controllers (which preceded ATA controllers), but the latest ATA standards have much more complex protocols and instruction sets that include optional commands and protocols providing such advanced optional-use features as sizable hidden system storage areas, password security locking, and programmable geometry translation.

Some XT-IDE adapters were available as 8-bit ISA cards, and XTA sockets were also present on the motherboards of Amstrad's later XT clones as well as a short-lived line of Philips units.