![]() | This ![]() It is of interest to the following WikiProjects: | |||||||||||||
|
![]() | This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later. |
The 8-bit and 16-bit bus pinouts have an error; the IRQ1 pin should be labeled as IRQ2 pin. IRQ0 and IRQ1 are not available on the ISA bus, as they go directly to the relevant hardware (programmable interval timer and keyboard controller). 91.153.27.229 ( talk) 08:29, 17 July 2008 (UTC) Jepael
I think the information here is out of date, so far as I know no PCs' are being made with the ISA bus, typically they have several PCI slots and usually an AGP slot.
Nezumi Replies: by the way. ISA Bus speed is 8MHz for a 16 bit ISA and 4.77 for a 8 bit ISA
There's still significant demand for ISA on industrial motherboards, apparently; legacy devices, plus the fact that many of them don't need all that much bandwidth but *do* need a lot of different devices plugged into them. This last rules out PCI, and USB has close to zero real-time capacity. I have in my lap a catalogue for iei electronics with P4 motherboards with two ISA slots; www.ieiworld.com, if you don't believe me. I'll leave it to the cleverer to edit the actual text.
Apart from internal use on current PC-compatible systems - I'm not so sure about this: most current motherboards use an LPC bus instead, to save having to route all the traces ISA requires.
please tell me or die
... The top picture is a photo of the plastic ISA-type connecting slots that ISA circuit boards plug into. The picture is taken at a strange angle, so look at the PCI article to see what these slots look like when viewed directly at them. The drawings below the picture are just top views of the connectors with notes indicating what each physical connection is used for. It is like unplugging your computer from the wall, pointing the prongs of the plug at your face and putting little labels on them to explain what each of them does. So now I don't die, huh? R.Giltner 20:14, 14 December 2006 (UTC)
I have got a situation in my project to use 5 PCI video frame grabber cards and to process all card datas simultaneously.
As far as i recall, the name ISA did not surface untill the 16 bit extension of the IBM-PC slot. So, it's a bit like referring to a Model B as a Model T--which i'm sure also happens. [Then there's the whole Model A vs `Model A' nonsense, but i digress.]
—
StationaryTraveller
03:56, 11 May 2006 (UTC)
The Industry Standard Architecture, or ISA, bus originated in the early 1980s at an IBM development lab in Boca Raton, Florida. The original IBM Personal Computer introduced in 1981 included the 8-bit subset of the ISA bus. In 1984, IBM introduced the PC-AT which was the first full 16-bit implementation of the ISA bus.
The "AT bus", as IBM originally called it, was first documented in an IBM publication called the PC-AT Technical Reference. The Technical Reference included schematics and BIOS listings that made it easy for other companies like Compaq to produce IBM compatible clones. The companies producing IBM compatibles could not use the "AT bus" name however since IBM had protected it with a trademark. In response, the industry coined "ISA" as a new name for the bus that was eventually adopted by everyone including IBM.
Although the PC-AT Technical Reference included detailed schematics and BIOS listings, it did not include the rigorous timings, rules, and other requirements that would make it a good bus specification. As a result, the various implementations of ISA were not always compatible with each other. Over time various ISA bus specifications were produced in an attempt to alleviate the compatibility problems. But unfortunately these specifications did not always agree with each other, so no single specification for the ISA bus was ever developed.
I put this reference to clarify the industry position, and to validate the authors concern that since he was probably there while it was happening, as was I, that the quoted source was correct, and invalidated the premise of the article that the ISA Bus began with the IBM Personal Computer AT, and was a 6Mhz 16-bit bus, and NOT an 4.77Mhz 8-bit bus, for the IBM Personal Computer PC and the IBM Personal Computer XT. — Preceding unsigned comment added by 173.200.183.146 ( talk) 21:35, 24 July 2012 (UTC)
This article states that the ISA bus allows for bus mastering and has DMA channels, but the ISA bus was controlled by a separate DMA controller. From what I've read this was one of the main reasons why PCI rendered ISA obsolete... PCI devices could take control of the bus themselves, so nothing external was required to control traffic. Could anyone clarify how this works, and the differences between ISA and PCI bus mastering? How is it that an ISA device has DMA channels but still had request/ack channels... is this just part of the device handshaking protocol? —Preceding unsigned comment added by 66.142.239.75 ( talk) 17:41, 16 September 2007 (UTC)
Found the refrence: "-MASTER
Master is used by an ISA board along with a DRQ line to gain ownership of the ISA bus. Upon receiving a -DACK a device can pull -MASTER low which will allow it to control the system address, data, and control lines. After -MASTER is low, the device should wait one CLK period before driving the address and data lines, and two clock periods before issuing a read or write command."
This is how the first accelerator cards, and video cards, and ram cards worked. ----~~
How were clone manufacturers able to use ISA when it was created by IBM? Why did not IBM ban this? Teveten 14:59, 4 October 2007 (UTC)
In an old zenith datasystems 386DX machine (made in '86 or '87) there is an vesa local bus like extention to the good old 16 bit ISA bus, except that the print connector sizes are the same as in the isa bus (the connectors are a little more than doubled in length).
The following add on cards are connected to this bus: - a card carrying the processor and bios - two huge cards carring 4MB of XT like memory chips each. - the video card (CGA/EGA connector), which includes an serial mouse port on the video card. - two MFM Harddisk drive controllers. Only those disks to one of the controllers are recognized by the OS. It seems the other one does provide several MB of virtual memory per huge MFM disk connected - and one that seems to be a data accuisition card.
It seems the memory bus is extended (like VESA) to those extention cards, aim: to be able to do DMA?
Is this an standardized update / extension for the ISA bus, or is it a rare extension to ISA16? —Preceding unsigned comment added by 213.84.80.86 ( talk) 16:35, 23 November 2007 (UTC)
The 386 was still in the early years of PCs where few standards existed like today. Naturally because of this, motherboards and their configurations varied wildly between manufacturers. The elongated slot on the Zenith system was likely a proprietary slot created by Zenith to take advantage of the 386's 32 bit bus. Some of them may be EISA slots, but I wouldn't know without seeing a picture. One thing I can guarantee though, it isn't any kind of VESA slot. Ggigabitem ( talk) 07:07, 16 July 2009 (UTC)
The 386 extention by Zenith to ISA is called a 386 slot. See Google 'Zenith 3300' for more information. Some other manufacturers also have separate 386 slots on their early 386 boards. Purpose seems to be extending the memory bus to >286 capabilities. —Preceding unsigned comment added by 213.84.80.86 ( talk) 18:10, 23 November 2007 (UTC)
By the picture of 16 Bit ISA pins, there seems to be no irq15 pin. In Barry Brey's book "The Intel Microprocessors 8086/8088 <...> Pentium 4 Architecture, Programming, and Interfacing", 6th edition, D6 pin is called IRQ15 instead of IRQ13 on the picture. One more link: http://www.byminsk.com/isa.htm - the table there says D6 is IRQ15, not 13. I think it's really irq15, because irq13 is FPU error interrupt, and it shouldn't be used by ISA devices, while irq15 _is_ used by secondary IDE controller. If i am right, fix this error in the picture someone pls (i won't do this 'cause i am not quite sure that i'm right). —Preceding unsigned comment added by 91.192.188.185 ( talk) 15:32, 16 September 2008 (UTC)
[One of the goals of the Gang of Nine was to standardize the AT bus, which notably had holes and ambiguities left in the specifications for it in IBM's Technical Reference manuals. For example, the bus speed was defined as the CPU clock speed, with no upper limit for future computer models explicitly defined, and the signal timing was defined only implicitly by the specifications of the Intel CPUs used and the electronic circuit schematics for the IBM implementations of the bus, which IBM published in the Technical Reference manuals. (By the amount and type of data IBM provided, it clearly appears that IBM only intended it to be used to make third-party attachments, peripherals, software and accessories for IBM-built computers.) For widespread compatibility between " clones", it was necessary to "nail down" all of the unspecified technical parameters and limits, as the clones were not pure identical "clones" but actually differing compatible machines which duplicated only the general IBM architecture, and not every specific device used with that architecture. Therefore, with the Gang of Nine performing this standardization work, it is likely that they developed and distributed a written standard specification for ISA, though (to this author's knowledge) they may not have made it publicly available. This would have been an at least semi-open trade-association standard similar to USB or the Philips Compact Disc standard " Rainbow Books", not an international standard recognized by a standards body like ISO, IEEE, or IEC.] This needs to be referenced before adding. -- Wtshymanski ( talk) 14:56, 19 October 2008 (UTC)
Is this referring to DMA? For general memory or I/O port transfers, each individual bus cycle takes a full, independent 24-bit address with the data length (8 or 16 bits) and memory or I/O selected by the *MEM CS 16 and *IO CS 16 lines. The IBM AT technical reference manual, the original and authoritative [but not comprehensive or always thorough] definition of the AT bus, makes no reference to any constraints for mixing 8- and 16-bit cards.)
Like many "info"-boxes on Wikipedia, the box lies if it says "8 MB/S". Firstly, does it mean "megaBYTE" or "megaBIT"? Given our tight editorial control, we don't know which one is meant (let alone how many are in a "mega" anything). Secondly, it varies by slot - all the slots are more or less synchronous, but an 8 bit slot has only half as many data bits as a 16 bit slot (duh!). Thirdly, it's not standardized...some editors may not recall the sorting through cards to come up with a combination that worked with the new machine that clocked its bus a tiny bit faster than a 5150. People who make infoboxes on Wikipedia appear as if they know a lot about boxmaking but don't choose to know a lot about the subject matter. -- Wtshymanski ( talk) 14:19, 7 December 2010 (UTC)
"19-Slot (7xPCI, 12 ISA) PICMG Backplane,3rd generation design of ACTI-Backplane, Enhanced PCB thickness to prevent bending, As many as 11 ISA slots for legacy bus applications, More PICMG CPU slots to fit versatile SBC boards, Specially designed capacitor which lowers the ESR and prevents explosion, Well-designed power ensures sufficient power is delivered to every slot." [3]
8-bit I/O is the least complex signaling. Such bus phase occurs when AEN = 0, IOR/IOW = 0, RESET = 0, A0 - A9 = card address which indicate that D0 - D7 is available. Maximum transfer time with an 8 MHz bus clock is 500 ns or 4 CLK cycles. Driving I/O CS16 signal 16-bits from card and SBHE is driven high by the motherboard when D0 - D15 is valid. [1] [2] [3] [4] [5]
References
What is the maximum designed length allowed for the bus signal wires?
I'm hacking an old device that had an embedded motherboard which can not be replaced, so using ribbon cables and card-edge slot adapters, I've sort of extended the ISA bus out of the one box and into the rear of another PC to use one of its ISA slots. The ribbon cable length is something like two feet long, and this is working just fine. Seems odd for it to work so well.
I thought for sure either the computer wouldn't POST or the ISA device would fail randomly but it's all working fine. I can not find info on the max length of the bus anywhere, so who knows, this may be operating well within whatever the spec actually is. Though I will probably wrap the extender ribbon in foil to provide RF shielding outside the normal RF-enclosure. 216.56.13.252 ( talk) 01:54, 17 September 2011 (UTC)
"A derivative of the AT bus structure is still used in the PCMCIA standard, Compact Flash, the PC/104 bus, and internally within Super I/O chips." Big discusion of ATA/IDE in the article, but the introduction doesn't even mention it. — Preceding unsigned comment added by 203.206.162.148 ( talk) 09:55, 17 September 2014 (UTC)
Use of the term "XT-IDE" in reference to the 8-bit version of IDE used in vintage XT-class machines should be avoided to prevent confusion with the modern open-source XT-IDE cards, which provide an ATA-compatible interface for XT-class machines, and is in fact totally incompatible with these vintage 8-bit IDE drives. The vintage 8-bit drives and interfaces were commonly known as IDE-XT when they were in current use in the late '80s and early '90s, or today also by the retronym XTA. — Preceding unsigned comment added by 74.105.4.154 ( talk) 02:00, 5 October 2021 (UTC)
I believe pin B4 of the connector is mislabeled. It says IRQ2, which agrees with http://www.hardwarebook.info/ISA#Pinout, but that is not an authoritative source. Intel's ISA Bus Specification and Application Notes (page 62), linked in the Further Reading Section specifies that pin as IRQ9, as does the PC/104 spec (page 20), and so does the user manual of a PC/104 compute board I'm designing a back plane for. -- 180.150.103.66 ( talk) 05:18, 29 January 2022 (UTC)
There's no mention of the physical sizes of cards meeting the standard, whereas it is covered in the articles on PCI and PCI Express. Though, maybe those articles are just unusually good, given AGP and PCI-X are also missing it. -- Roxor128 ( talk) 03:28, 31 August 2022 (UTC)