Probably the 18 pin 1M ones on the 4th page of this...
http://matthieu.benoit.free.fr/cross/competit … s_reference.pdf

But that's something of a half educated guess.

You've got 36, so I guess that includes parity, buggers aren't laid out where it's easy to tell the banks, so you can swap in 9 chips to try.

Deksor wrote:

Hello everyone ! So I've bought the other day a full 286 system. It features a 12MHz cpu and 1MB of RAM. But I find 1MB of ram r […]
Show full quote

Hello everyone !
So I've bought the other day a full 286 system. It features a 12MHz cpu and 1MB of RAM. But I find 1MB of ram rather limiting, especially for a 286 that new (it's from 1989). I'd like to upgrade it to 4MB (the name of the mobo evokes that it supports it (there's "4096K" in it's name). The ram is separated on 36 ram chips (each of them must be 256kbit. There's "HM51256P-10" written on it. Also there seem to be 2 kinds of chip sockets for each ram chip. These have 4 more pins than the other one so that's probably for bigger chips.

The problem is I don't know what kind of chip I must buy. Sure that must be 1Mbit chip, but what kind are theses ?

By the way here's a photo of the mobo

IMG_20171101_165605.jpg

And here's a closer look to the ram area

IMG_20171101_165616.jpg

Someone correct me if I'm wrong, but that looks maxed at 1MB.

I can't quite make out the writing on the chips, but they all have "...256" on them, so probably 41256 or some variation. Each set of 9 chips being 256k. At least that's how it was on my 286.

EDIT: I've never seen 1MB chips like the ones BitWrangler linked. Neat!

The second Google result for "HM51256P-10" is a datasheet for that chip, which says it is indeed a 256kbit chip. The key things are 256k, 1-bit, 100ns. So when looking for replacement chips, you want ones that are 1-bit and 100ns or faster.

The actual capacity you can get depends, as you have mentioned, on the number of pins. Larger chips need more address pins. If you can find a manual for the board, that will tell you exactly what types of chips it supports and where to install them.

To get 4 mb instead of 1 mb, you would simply replace all 1256 by 4256 chips. They take the additional pins.

You have a Suntac board, see here 😉
Re: Suntac 80286 Mainboards

You need
18 x 411000
in Bank 0 + 1 for 4MB, see here
download/file.php?id=33353
mode 6 or 7

Okay I'm dumb ... I had the manual of the motherboard 🤣

That suntac board is simillar to mine, but it's not exactly like mine. The manual of my board says that I need 18 pins 511000 chips to upgrade it. The problem now is ... price. Buying 36 of these chips seems to be quite costly. I think I'll wait a bit or try to salvage something that uses that kind of chip ...

Thanks for helping ^^

Can you scan your manual and add your BIOS to the Suntac thread - thanks! 😀

I don't have anything to scan things unfortunately ... but I can take several photos

Deksor wrote:

Buying 36 of these chips seems to be quite costly. I think I'll wait a bit or try to salvage something that uses that kind of chip ...

Yes, not near as much as when they were new though, could be paying $25 a chip then. Often, 16bit ISA expansion boards have that RAM on, in a 286 they're not really slower using on the expansion board as putting it on the motherboard though. Also 4MB is nice, but I doubt anything you can run on a 286 will really use more than 2MB of expanded memory, at least unless you want to edit huge spreadsheets or documents. So if you turn up a 2MB ISA expansion board, even with the wrong chips on, just whack that in and be happy. But if you're determined to find them, other sources than PCs would be industrial control systems based on VME bus or S100 bus, though the latter are collectable enough now that pulling chips off one might be regarded as vandalism when the board would be of interest to S100 collectors. Ditto the idea of pulling it from arcade boards.