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Comment by Suppafly | Hacker News Reader

Is the "based on the IBM 5170 AT PC" bit because he started with a 5170 design and updated to 286 piecemeal instead of cloning a 286 design directly?

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5170 (IBM AT) was a 286 design. The 5150 (IBM PC) and 5160 (IBM PC XT) were the previous 8088-based systems. Sounds like it's described as "based on" because it's heavily reverse engineered, modified to use more readily available components where possible, and then improved to 20MHz capability over the original 5170's 6/8MHz.

Lots of info on the 51xx series of machines is here: https://www.minuszerodegrees.net/index.htm

Ah, thanks I misunderstood.

>Sounds like it's described as "based on" because it's heavily reverse engineered, modified to use more readily available components where possible, and then improved to 20MHz capability over the original 5170's 6/8MHz.

I wonder if he looked at any clone motherboards from that time, or a few years later? 16MHz and 20MHz 286s were quite common before the 386 took over, and they probably had to make some changes too (and came a few years after the PC AT, and so probably had a lot of improvements; the AT came out in 1984, but the clone 286s were still pretty strong in the late 80s).

I was thinking 286's were faster than was being mentioned, but I suppose his design was speeding up a design from the beginning of the era instead of copying a later design.

286s were quite fast for DOS applications in their later days; they were actually faster than the newer 386SX systems that were competing against them, but of course they couldn't do 32-bit operations.

There's also the somewhat odd "XT/286" 5162, which was somewhere in between the two, and closer to the AT than the XT.

https://dfarq.homeip.net/ibm-5162-pc-xt-286-the-at-in-xt-clo...

From what I gathered the 5170 was[1] a 286 design?

In any case, from the description:

Luckily I found an Ebay auction which offered an IBM 5170 mainboard for a very reasonable price.

I proceeded to draft modern KiCad schematics for the 5170 and subsequently modified the IBM designs to suit this project as much as possible.

[1]: https://en.wikipedia.org/wiki/IBM_Personal_Computer_AT

Yeah I was confused, I assumed all the 51xx were the older 8088 models.

Taking an 80286 and reclocking it in order to get an 8-bit CPU to work as a 16-bit 80486 processor. Ambitious project.

The IBM 286 can operate at frequencies below 20MHz as well.

>http://www.machine-information-systems.com/286_Processor.htm...

Link to separate repository: https://github.com/rodneyknaap/atx-486at-mainboard

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