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I don't have an Intel Inboard 386/PC, but I have a plan to buy it in the future. When I read its manual, there was no support for XT clones.

It says:

Install the Inboard 386/PC only in the computers listed below.

The Inboard 386/PC is designed to work in the following computers:

  • IBM PC (all models)
  • IBM PC XT (all models except IBM PC XT/286)
  • COMPAQ PORTABLE and PORTABLE PLUS
  • Tandy 1200 HD

The Inboard 386/PC isn't compatible with 8086-based computers, such as the COMPAQ DESKPRO.

I want to know if Intel Inboard 386/PC work on XT clone systems not mentioned above...

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  • 2
    Surely it depends on the fidelity of the clone to the original?
    – dave
    Commented Jul 20, 2022 at 16:58
  • The Kaypro 286i was the very first "99% software compatible" PC. (I was working at Tektronix at the time and we were burning through pretty much all of the clones trying to find cheaper replacements. The Kaypro 286i was the first one we found that could measure up. And that was only after the 80286 was out. Not before. Keep in mind I'm not talking about hardware compatibility. Just the BIOS and all the other necessary elements to allow it to run most software we needed to run. So I do NOT have direct information regarding hardware compatibility for a add-in board like this. Only a note.
    – jonk
    Commented Jul 20, 2022 at 18:43
  • It's just my opinion that if you wanted full up compatibility prior to the Kaypro 286i, then you pretty much only had IBM products to work with. It's all I was able to actually use during those earlier years, despite the high cost at the time.
    – jonk
    Commented Jul 20, 2022 at 18:45
  • The inboard is connected to an XT-slot (8-bit ISA slot) and to the i8088 socket using a ribbon cable (the i8088 CPU is removed and the ribbon cable is plugged to the socket). For this reason, it only works with i8088-based computers. My father owned an i8088-based clone (allegedly self-built by the pre-owner); he added an Inboard 386 to that PC so it definitely works on clones, too. Commented Jul 21, 2022 at 5:46

3 Answers 3

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In the 1980s, there were dozens, if not hundreds, of companies making PC clones. Some used very careful and detailed engineering practices which systematically ensured that they would abide various timing constraints throughout the entire allowable ranges of manufacturing variations, temperature, and other such factors, but signal timings in an a 4.77 MHz 8088-based PC were sufficiently forgiving that such care wasn't needed to produce a machine that would work reliably with most common expansion cards, and thus many designers of PC clones did not exercise such care.

Intel was a sufficiently important company that it could ask IBM and Compaq to agree that they would not make any design changes to the machines that would cause deviations from the spec, without clearing such changes with Intel first, in exchange for having Intel endorse those companies' PCs as being compatible with the Inboard, and IBM and Compaq used a sufficiently rigorous design methodology that they could ensure that things like board layout revisions would not cause such deviations. A product like the Inboard would be likely to work just as well on many of the other machines whose designers made no effort to distinguish themselves from the PC in any way other than price, but it would have been impractical for Intel to reliably distinguish machines that would be proven to work by design, those that would likely work but whose could not be proven, and those that would in fact work.

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When I read its manual, there was no support for XT clones.

XT clone is a subsumption of all machines that are build exactly after the plans for an IBM PC-XT and thus work like a PC-XT, thus they are covered as soon as an PC-XT is covered.

In contrast an IBM PC-XT compatible computer may or may not be covered. It would need a specification how compatible it is. A 100% PC-XT compatible in turn is a clone.

The Inboard 386/PC is designed to work in the following computers: [... IBM PC XT (all models except IBM PC XT/286) [...]

This covers as well all PC-XT clones / 100% compatible.

I want to know if Intel Inboard 386/PC work on XT clone systems not mentioned above...

Well, if it's a PC-XT clone (aka 100% compatible) then it will work. If that machine only partially compatible it may or may not work, depending how compatible it is. The same issue arises with all expansion (cards).

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  • There are probably quite a few xt-style machines which would work with almost everything designed for the PC but fail with the Inboard. Since (according to another post) the card includes a daughterboard that plugs into the main CPU socket and is connected to the Inboard via ribbon cable, the board would be uniquely dependent upon the physical location of the main CPU and the amount of space around it. I would not be at all surprised if some motherboards would be electronically perfect, but nonetheless unusable with the Inboard because of such physical constraints.
    – supercat
    Commented Jul 21, 2022 at 19:40
  • @supercat you mean the cable might not fit?
    – RETRAC
    Commented Jul 21, 2022 at 21:50
  • @RETRAC: Pretty much. I don't know whether there's anything on the assembly that plugs into the motherboard CPU socket, but I would expect that either (1) that assembly contains circuitry to clean up signals that are carried via the ribbon cable, in which case the board would likely be bigger than an 8088 CPU, and might collide with tall components on the motherboard that are too close to the CPU socket, or (2) it doesn't contain such circuitry, in which case the ribbon cable would need to be fairly short, making it difficult to route around obstacles.
    – supercat
    Commented Jul 21, 2022 at 22:22
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"The Inboard 386/PC isn't compatible with 8086-based computers, such as the COMPAQ DESKPRO."

This likely referred to literal 8086 or 80c86 (as opposed to 8088!) based PCs, which tended to have subtle hardware differences (bus control/glue logic) from designs closer to the original XT. These typically were branded systems (eg the Compaq DeskPro mentioned, or the Toshiba T1200), not generic clones (which usually were based on 8088 based mainboards).

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