VOGONS

286 Memory compatibility

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First post, by Jackal1983

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So, on a lark last week I bought a fairly late (circa 1991) HT12A based mobo on ebay hoping that there wasn't any battery leakage (pics didn't show that area all that well), and I guess I got lucky, the board looks damn near mint condition. It'll be getting a Harris 286-25 in the near future as well as a crystal swap (bought some sockets for that) as well as a 20 mhz 287 if I ever see one come up. That brings up the question of memory: It came with 80ns 3-chip parity SIMMs. So my question is this: Just what 30 pin simms are compatible with a 286 mobo? I'll assume I need parity for now and the documentation I've found implies 4mb is the max. Is FPM compatible with 286s? Oh and pics will be coming!

Reply 1 of 7, by kixs

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Get (any) 60ns 1MB SIMMs, 3 or 9 chip should work fine. If you plan on overclocking, memory could hold you back for 0-ws operation as some users used even 45ns SIMMs to get it going. There is no point in going from 20 to 25MHz if it requires 1-ws.

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Reply 2 of 7, by Jackal1983

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kixs wrote on 2021-04-08, 17:52:

Get (any) 60ns 1MB SIMMs, 3 or 9 chip should work fine. If you plan on overclocking, memory could hold you back for 0-ws operation as some users used even 45ns SIMMs to get it going. There is no point in going from 20 to 25MHz if it requires 1-ws.

So FPM works in 286s?

Reply 4 of 7, by Jackal1983

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kixs wrote on 2021-04-08, 18:05:

Yes.

Nice. I'll keep an eye out for any deals. There's also another Vogons member building 45ns 1 meg sticks I plan to keep an eye on (nonparity, so hopefully I can disable that in the bios, and they're single chip simms so I should probably wait till someone tests these in a 286). For now I'll go with a 1 meg 60ns kit I just found for about 12 bucks.

Reply 6 of 7, by Jackal1983

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weedeewee wrote on 2021-04-08, 18:27:

Is the HT12A chipset suited for 20 or 25MHz operation? I recall it only being for 12 or 16MHz.

It's one of the ones I've seen most often in fast 286 builds (the other being a VLSI chipset I think).

Reply 7 of 7, by kixs

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weedeewee wrote on 2021-04-08, 18:27:

Is the HT12A chipset suited for 20 or 25MHz operation? I recall it only being for 12 or 16MHz.

There were motherboards with HT12A and Harris 20Mhz with 40MHz oscillator from Octek . I have two of them. Plan is to try and switch the oscillator to 50MHz to test the 25Mhz operation. I hope at least one of the two will work fine 😉

Visit my AmiBay items for sale (updated: 2025-08-01). I also take requests 😉
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