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January 2014 ISA Industry Standard Architecture One and five ISA slots on a Year created 1981 ; 38 years ago 1981 Created by Superseded by1993, 1996 Width in bits 8 or 16 No.
The bus was largely with slot computers definition 8-bit bus of the -basedincluding the as well as.
The ISA term was coined as a by competing PC-clone manufacturers in the late 1980s or early 1990s as a reaction to IBM attempts to replace the AT-bus with its new and incompatible.
The 16-bit ISA bus was also used with 32-bit processors for several years.
An attempt to extend it to 32 bits, called EISAwas not very successful, however.
Later buses such as and were used instead, often along with on the same.
Derivatives of the AT bus structure were and still are used inthe standard,the bus, and internally within chips.
ISA originated as an 8-bit system.
In 1988, the 32-bit EISA standard was proposed by the "Gang of Nine" group of PC-compatible manufacturers that included Compaq.
The 16-bit version was an upgrade for the motherboard buses of the Intel CPU used in the IBM AT.
The ISA bus was therefore synchronous with the CPU clock, until sophisticated buffering methods were implemented by chipsets to interface ISA to much faster CPUs.
ISA was designed to connect peripheral cards to the and allows for.
Only the first 16 of main memory is addressable.
The original 8-bit bus ran from the 4.
The also used the 16-bit bus.
ISA was also used in some non-IBM compatible machines such as Motorola -based 68020 and 68030 workstations, the short-lived and the later -based.
Companies like improved the AT bus's performance but in 1987, IBM replaced the AT bus with its proprietary MCA.
MCA overcame many of the limitations then apparent in ISA but was also an effort by IBM to regain control of the PC architecture and the PC market.
MCA was far more advanced than ISA and had many features that would later appear in PCI.
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 EISA and the later VLB.
VLB used some electronic parts originally intended for MCA because component manufacturers already were equipped to manufacture them.
Both EISA and VLB were backwards-compatible expansions of the AT ISA bus.
Users of ISA-based machines had to know special information about the hardware they were adding to the system.
While a handful of devices were essentially "", this was rare.
Users frequently had to configure parameters when adding a new device, such as the line,or channel.
MCA had done away with this complication and actually incorporated many of the ideas first explored with MCA, though it was more directly descended from EISA.
This trouble with configuration eventually led to the creation of ISA PnP, a system that used a combination of modifications to hardware, the systemand software to automatically manage resource allocations.
In reality, ISA PnP could be troublesome and did not become well-supported until the architecture was in its final days.
PCI slots were the first physically-incompatible expansion ports to directly squeeze ISA off the.
At first, motherboards were largely ISA, including a few PCI slots.
By the mid-1990s, the two slot types were roughly balanced, and ISA slots soon were in the minority of consumer systems.
ISA slots remained for a few more years, and towards the turn of the century it was common to see systems with an AGP sitting near thean array of PCI slots, and one or two ISA slots near the end.
In late 2008, even floppy disk drives and serial ports were disappearing, and the extinction of vestigial ISA by then the from chipsets was on the horizon.
PCI slots are "rotated" compared to their ISA counterparts—PCI cards were essentially inserted "upside-down," allowing ISA and PCI connectors to squeeze together on the motherboard.
Only one of the two connectors can be used in each slot at a time, but this allowed for greater flexibility.
ATA has its origins in that integrated a HDD and a HDC onto one y&i slots of fun />This was at best awkward link at worst damaging to the motherboard, as ISA slots were not designed to support such heavy devices as HDDs.
The next generation of drives moved both the drive and controller to a drive bay and used a ribbon cable and a very simple interface board to connect it to an ISA slot.
ATA is basically a standardization of this arrangement plus a uniform command structure for software to interface with the HDC within the slot computers definition />ATA has since been separated from the ISA bus and connected directly to the local bus, usually by integration into the chipset, for much higher clock rates and data throughput than ISA could support.
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.
The XT bus architecture uses a singlegiving eight vectorized and prioritized interrupt lines.
It extends the XT-bus by adding a second shorter in-line with the eight-bit XT-bus connector, which is unchanged, retaining compatibility slot computers definition most 8-bit cards.
The second connector adds see more additional address lines for a total of 24, and 8 additional data lines for a total of 16.
It also adds new interrupt lines connected to a second connected to one of the lines of the first and 4 × 16-bit DMA channels, as well as control lines to select 8- or 16-bit transfers.
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.
These can be found in almost every AT-class PC manufactured after the mid-1980s.
The ISA slot connector is typically black distinguishing it from the brown EISA connectors and white PCI connectors.
It is therefore possible to connect up to 6 devices that use one 8-bit IRQ each, or up to 5 devices that use one 16-bit IRQ each.
At the same time, up to 4 devices may use one 8-bit DMA channel each, while up to 3 devices can use one 16-bit DMA channel each.
Later motherboards or integrated used a separate clock generator, or a clock divider which either fixed the ISA bus frequency at 4, 6, or 8 MHz or allowed the user to adjust the frequency via the setup.
When used at a higher bus frequency, some ISA cards certain video cards, for instancecould show significant performance improvements.
This is because the MEMCS16 line is required to be set based on the value of LA17-23 only.
It is marketed to industrial and military users who have invested in expensive specialized ISA bus adaptors, which are not available in bus versions.
The bus, used in industrial and embedded applications, is a derivative of the ISA bus, utilizing the same signal lines with different connectors.
IDE and more recently 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.
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 controllersbut 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 most forms, ATA ran much faster than ISA, provided it was connected directly to a local bus faster than the ISA bus.
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 's later XT clones as well as a short-lived line of 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.
AT-IDE type interfaces only entered the keyboard-cased Amiga line upon introduction of the and which have an and 44 pin connector.
Many owners removed the 2,5 inch bracket and installed a 3,5 inch drive with an adapter cable.
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.
Embedded controller chips and themselves provide services such as temperature monitoring and voltage readings through these buses as ISA devices.
However, despite there even having been books published on the P996 specification, it never officially progressed past draft status.
Retrieved 17 March 2016.
The New York Times.
Retrieved 6 January 2015.
Retrieved 3 May 2018.
Retrieved 3 May 2018.
This article is based on material taken from the prior to 1 November 2008 and incorporated under the "relicensing" terms of theversion 1.
Interfaces are listed by their speed in the roughly ascending order, so the interface at the end of each section should be the fastest.
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Slotted definition, a narrow, elongated depression, groove, notch, slit, or aperture, especially a narrow opening for receiving or admitting something, as a coin or a letter.
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