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I have several 286, 386 and 486 motherboards that I would like to use. My problem is that while I have all of the components to make them functional, I don't have spare cases to put them in. Ideally, I would put them in period correct AT cases. However, I am finding it difficult and/or expensive to source AT cases. You would think something like AT cases would be cheap and easy to find. Since they made millions upon millions of them.

Many times, the shipping alone is more than a modern ATX case shipped to my house. And before you mention it, I've looked in many thrift stores, eBay, Craigslist, etc. in my area.

So I was thinking of just getting the most boring, plain white ATX cases I can find and try to put the motherboards in there.

First off, I know I will have an issue with AT to ATX power. I prefer using modern PSU's anyway so what I have done previously is just buy a modern ATX PSU and then buy an ATX to AT power button converter off eBay (these are cheap). So I have power covered.

The next hurdle is going to be the AT keyboard connector. Many times, AT cases have a hole drilled into the case for the AT keyboard connector. So this might be an issue.

Other than that, what are the other pitfalls I may run into? I don't have a spare ATX case at the moment to test this theory.

I don't mind modding a case but if it's going to be lots and lots of work, I may just pay the premiums for AT cases.

Thanks.

  • 3
    The AT keyboard connector is in the same place as the IO shield on ATX mainboards, so it's just a matter of making your own IO shield to keep the dust out. For the PSU, recall that an ATX power supply does not provide a -5V rail which is needed for some ISA cards. A good converter should be able to generate it though. – fuz Jan 21 at 17:06
  • @fuz Older ATX power supplies have -5V, and they're probably easier and cheaper to find that converters that will actually generate -5V. – Ross Ridge Jan 21 at 19:13
  • Good point on the -5V. I totally forgot about that one. – cbmeeks Jan 21 at 20:08
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    Do you need cases at all? Look here for example: esato.com/archive/t.php/t-74357,1.html :) – Arvo Jan 22 at 14:19
  • Old AT cases are built like a tank. Shipping them are quite expensive. I have one that is AT/ATX compatible, started as a Pentium 200 and upgraded over 10 years into a Core 2 Duo E6300. The case is super heavy, and feels sturdier than some of the "server" cases I worked on. When transporting it I regularly just sit on it when waiting for a bus or something. – Nelson Jan 23 at 7:08
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Some issues you may encounter are:

  • Motherboard size. An AT motherboard is 13 inches from front to back, while the ATX standard mandates 9.6 inches. If a case takes an Extended ATX motherboard it should take an AT one.
  • Mounting pillars / holes. On an AT motherboard the position of the holes is not precisely defined by the standard, whereas ATX is more rigorous. Early ATX cases tended to have holes for all possible mounting pillar locations, while later ones may only support those defined in the ATX standard. If your case has mounting pillars that can't be removed, and they don't correspond to holes in the AT motherboard, you'll need to block them off with an insulator (for example, a plastic screw) so they don't cause shorts on the motherboard. (Aside: This can also happen mounting an AT motherboard in an AT case not designed for it).
  • The power switch. The AT to ATX converters I've seen are designed for an AT-style power switch (toggle on/off) rather than an ATX-style switch (momentary pushbutton). What I've done when using them is to mount a toggle pushbutton switch in a spare drive bay, and use that as the power switch rather than the case's own.
  • The keyboard connector. When an AT motherboard is mounted in an ATX case, the keyboard connector will line up with the rectangular opening where the I/O shield would normally go. I/O shields with a single circular hole for an AT keyboard did exist (one's pictured on Wikipedia) but I'm not aware of a source for them.
  • The turbo button. It's very unlikely that your case will have one, so if your motherboard has a connection for one you'll either need to jumper it to the required position, or modify the case to add a toggle button (as for the power switch).
  • The power LED. AT, and older ATX cases used a 3-pin Berg connector for the power LED, with the middle pin blank. Later ATX cases use a 2-pin Berg connector, so you may have to replace the connector to make it fit the motherboard.

Given all of the above caveats, there are combinations which work. The notes above come from successfully mounting AT motherboards from the 486/Pentium era in ATX cases from the late 1990s.

  • That pretty much covers it! As far as size goes, Baby AT boards will have a better chance of fitting in an ATX case. See also this Vogons thread and this detailed installation. The airflow will be different but that shouldn’t cause any issues. – Stephen Kitt Jan 21 at 17:16
  • Very good answer. You definitely hit some points I had forgotten. I think using a sturdy piece of aluminum would work as a back plate (with some careful drilling/cutting). I really like the idea of using a faceplate for buttons too. – cbmeeks Jan 21 at 20:12
  • If you don't want to waste a whole bay, you can mount the buttons on a 3.5"-to-5.25" mounting bracket, with a floppy drive or zip drive in between them. – john_e Jan 22 at 0:52
  • The only thing I would add is with some motherboards you may have issues with a shortage of rear expansion card openings in the ATX case. This will especially apply to 486 motherboards with the 3 VLB slots at the bottom. This will leave you with only 3 (or less!) open ISA slots with cutouts on the case which can be quite restrictive, if you don't have any VLB cards and want to install I/O, video, audio, and a network card all in the ISA slots. Similarly with newer 486 and Pentium boards you may have most of your PCI slots blocked with just the ISA slots open. – mnem Jan 22 at 13:54
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    Slot spacing would only be an issue on a very old board, such as the original 5150 - the slots on the IBM 5160 XT and 5170 AT motherboards have the same spacing as ATX. – john_e Jan 22 at 20:54
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For a while, many PC cases were made to be both AT and ATX compatible. This would have been in the mid-1990s, during the changeover from Socket 7 to Slot 1 (Pentium II) and Super Socket 7 (AMD K6 series) when motherboards were made in both shapes. You could try looking for cases from that period, or from the early 2000s.

AT motherboards (in practice, usually these were "baby AT") devoted much more of their "back edge" to expansion slots and less to I/O, the latter being largely restricted to the keyboard port. However, that "back edge" is also much shorter than that of an ATX board. I think that means you could mount an AT board so that (most of?) its expansion slots lined up with those of an ATX case, with the keyboard port showing through the I/O area.

I think the key feature you should look for is an extra row of mounting standoff positions midway between the ones needed for a Mini-ITX board; that's where the top edge of a Baby AT board goes. Many cases currently in production have a gigantic hole here instead, for access to the heatsink backplate that modern CPUs need.

This diagram should be enlightening.

I think it's still relatively easy to obtain early-2000s era cases like the Chieftec Dragon, which have the correct mounting holes for a Baby AT board.

4

I would say there are 3 main difficulties:

  1. AT power connector, versus ATX power supplies. As you've noted, adapters are available to convert from ATX to AT, you will just need to figure out what to use as a power switch. The AT used the main power supply disconnect as the system power switch, while ATX moved to 'soft power' via a motherboard connector.

  2. AT keyboard port. This is mostly a matter of cutting a hole if your ATX case doesn't have one (or it's not where you need it). A sheet metal nibbler may be useful for this. Take care to ensure that stray metal shavings don't end up where you don't want them.

  3. Form factor. This is the big one. Most ATX cases are too small for a full size AT motherboard, which was considerably larger than the PC and XT motherboards that came before, and the baby AT boards that came after. If you limit yourself to "baby AT" motherboards you will have better luck, especially if you use ATX cases that also support "baby AT". Baby AT and ATX are similar sizes, but not identical (ATX being 12" x 9.6" with the slots along the long edge, and baby AT being 8.5" x 13" with the slots along the short edge) so using a case that supports baby AT improves your situation dramatically. You may have to drill and tap new holes in the case to accommodate slightly different positions for the board standoffs.

  • 1
    "Baby AT" and ATX have similar sizes, but perpendicular to each other - the expansion slots are on the long edge of an ATX board, but the short edge of a baby AT board. So if you're saying ATX is 12" x 9.6", then baby AT is 8.5" x 13", not 13" x 8.5". – john_e Jan 21 at 20:30
  • @john_e that is quite correct, I'll edit that in to clarify. – Ken Gober Jan 23 at 16:52

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