Industry Standard Architecture
Past and current use
Past and current use
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ISA is still used today for specialized industrial purposes. 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. It was marketed to industrial and military users who had invested in expensive specialized ISA bus adaptors, which were not available in [PCI](/wiki/Conventional_PCI "Conventional PCI") bus versions.IEI Technology Corp: *IMBA\-9654ISA User Manual*, Rev. 1\.00, May 2008

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.ADEK Industrial Computers: *MS\-98A9 Product Specifications* Also, MSI released a modern motherboard with one ISA slot in 2020\.

The [PC/104](/wiki/PC/104 "PC/104") bus, used in industrial and embedded applications, is a derivative of the ISA bus, utilizing the same signal lines with different connectors. The [LPC](/wiki/Low_Pin_Count "Low Pin Count") bus has replaced the ISA bus as the connection to the legacy I/O devices on current motherboards; while physically quite different, LPC looks just like ISA to software, so that the peculiarities of ISA such as the 16 MiB DMA limit (which corresponds to the full address space of the Intel 80286 CPU used in the original IBM AT) are likely to stick around for a while.

### ATA

As explained in the *History* section, ISA was the basis for development of the [ATA](/wiki/Advanced_Technology_Attachment "Advanced Technology Attachment") interface, used for ATA (a.k.a. IDE) hard disks. Physically, ATA is essentially a simple subset of ISA, with 16 data bits, support for exactly one IRQ and one DMA channel, and 3 address bits. To this ISA subset, ATA adds two IDE address select ("chip select") lines (i.e. address decodes, effectively equivalent to address bits) and a few unique signal lines specific to ATA/IDE hard disks (such as the Cable Select/Spindle Sync. line.) 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 ATA device registers are accessed using the address bits and address select signals in the ATA physical interface channel, and all operations of ATA hard disks are performed using the ATA\-specified protocols through the ATA command set. 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.

In mid\-1990s, the ATA host controller (usually integrated in chipset) was moved to [PCI](/wiki/PCI_bus "PCI bus") form.  A further deviation between ISA and ATA is that while the ISA bus remained locked into a single standard clock rate (for backward hardware compatibility), the ATA interface offered many different speed modes, could select among them to match the maximum speed supported by the attached drives, and kept adding faster speeds with later versions of the ATA standard (up to 133 MB/s for ATA\-6, the latest.) In most forms, ATA ran much faster than ISA, provided it was connected directly to a local bus (e.g. southbridge\-integrated IDE interfaces) faster than the ISA bus.

### XT\-IDE

Before the 16\-bit [ATA/IDE](/wiki/ATA/IDE "ATA/IDE") interface, there was an 8\-bit XT\-IDE (also known as XTA) interface for hard disks. It was not nearly as popular as ATA has become, and XT\-IDE hardware is now fairly hard to find. Some XT\-IDE adapters were available as 8\-bit ISA cards, and XTA sockets were also present on the motherboards of [Amstrad](/wiki/Amstrad "Amstrad")'s later XT clones as well as a short\-lived line of [Philips](/wiki/Philips "Philips") units. The XTA pinout was very similar to ATA, but only eight data lines and two address lines were used, and the physical device registers had completely different meanings. A few hard drives (such as the [Seagate](/wiki/Seagate_Technology "Seagate Technology") ST351A/X) could support either type of interface, selected with a jumper.

Many later AT (and AT successor) motherboards had no integrated hard drive interface but relied on a separate hard drive interface plugged into an ISA/EISA/VLB slot. There were even a few 80486 based units shipped with MFM/RLL interfaces and drives instead of the increasingly common AT\-IDE.

[Commodore](/wiki/Commodore_International "Commodore International") built the XT\-IDE based peripheral hard drive / memory expansion unit A590 for their [Amiga 500](/wiki/Amiga_500 "Amiga 500") and 500\+ computers that also supported a [SCSI](/wiki/SCSI "SCSI") drive. Later models – the [A600](/wiki/Amiga_600 "Amiga 600"), [A1200](/wiki/A1200 "A1200"), and the [Amiga 4000](/wiki/Amiga_4000 "Amiga 4000") series – use AT\-IDE drives.

### PCMCIA

The [PCMCIA](/wiki/PCMCIA "PCMCIA") specification can be seen as a superset of ATA. The standard for PCMCIA hard disk interfaces, which included PCMCIA flash drives, allows for the mutual configuration of the port and the drive in an ATA mode. As a de facto extension, most PCMCIA flash drives additionally allow for a simple ATA mode that is enabled by pulling a single pin low, so that PCMCIA hardware and firmware are unnecessary to use them as an ATA drive connected to an ATA port. PCMCIA flash drive to ATA adapters are thus simple and inexpensive, but are not guaranteed to work with any and every standard PCMCIA flash drive. Further, such adapters cannot be used as generic PCMCIA ports, as the PCMCIA interface is much more complex than ATA.


Can XT-IDE adapters be used with modern systems?