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I can see a PC benchmark sheet here.

It shows that the fastest XT is Juko XT, which runs at 12 MHz with NEC V20. I actually own one, and I've checked that it runs at 12 MHz. But another thing I know is that NEC V20 can operate even at 15 MHz, though I haven't found a computer that runs at the MHz.

What is the fastest 8088-compatible machine? If it's right that Juko XT is the fastest 8088-compatible machine, please also explain why NEC V20 was used to operate only up to 12 MHz on IBM PC-compatible computers.

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    How can a computer with a NEC V20 CPU be the fastest Intel 8088 machine?
    – tofro
    Commented Jan 18, 2023 at 12:06
  • Didn't the original XT run at 4.77MHz? I'd also be interested to understand why they didn't go to 28.62MHz and divide this by either 2 or 6 for the CPU's clock, and 6 for whatever else.
    – Omar and Lorraine
    Commented Jan 18, 2023 at 12:07
  • @tofro, I guess the question needs to be read as "8088 compatible" or something. OP, can you confirm this is what you mean?
    – Omar and Lorraine
    Commented Jan 18, 2023 at 12:09
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    What do you consider as 8088 compatible machine? Aren't all x86 CPUs backwards compatible with 8088? Can you be more specifc what kind of machines you are looking for?
    – Justme
    Commented Jan 18, 2023 at 12:26
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    I recently had my old 286 compute a poster-sized image of the Mandelbrot set, and it took almost a week to finish. Just for fun I did the same thing on a recent i5 which finished in 1.7 seconds. So the answer depends heavily on your definition of what is "8088 compatible"
    – Tommylee2k
    Commented Jan 18, 2023 at 14:15

1 Answer 1

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A rather pointless question, as soon as one deviates from the original XT, as more is possible. For example using a 16 bit bus version (8086/V30, like in M24 or Amstrad lifts performance by >30% (average) without increasing the clock. Even more at higher clock rates. Or upgrade with a 386 CPUs plug in boards, which was somewhat common back in the days. All XT class machines.

Even more, in the end many later machiens, all the way to rather recent Ryzen/Core/... CPUs are 8088 compatible, aren't they?

Now if we agree to stay with 100% XT designs using 8088, clock frequencies of 15 MHz and above were used already in the late 80s. These were about the last attempt by Taiwanese manufacturers to still sell existing designs

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  • I wouldn’t be surprised if add-on cards started to have bus compatibility issues at 12MHz, much less 15MHz. Heck, the turbo button existed to slow down the system for compatibility.
    – RonJohn
    Commented Jan 18, 2023 at 13:48
  • @RonJohn I saw it back then as slow down for software speed - some was simply too fast :)) Also, add-on cards may ofc slow down bus speed when accessing main board RAM/IO
    – Raffzahn
    Commented Jan 18, 2023 at 14:45
  • Memory didn't run at 15MHz. By the time faster Memory became available, 2nd generation processors were available.
    – david
    Commented Jan 22, 2023 at 10:17
  • @david XT class machiness were produced way into the 1990s. See this September 1990s Bye ad there are many more in the same issue and later ones. Just because a 2 (or here 4) newer CPU are available doesn't mean the 'older' are no longer sold. In that magazine you'll find 8088, 286, 386 and 486 sold in parallel, often by the same vendor.
    – Raffzahn
    Commented Jan 22, 2023 at 15:31

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