That's 9 bit = 8 bit + parity.
So, not necessarily 9-chip, 3-chip modules should work as well.

1M modules are plentiful and cheap, I would go for 4 or even 8 MB.

gmc wrote on 2023-10-26, 17:01:

Got my hands on 386DX40 motherboard which I'm trying to bring back to life. […]
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Got my hands on 386DX40 motherboard which I'm trying to bring back to life.

First issue is it's missing RAM. Found the m/b on this site :
https://theretroweb.com/motherboards/s/gemlight-gmb-386umc

and it takes 30 pin SIMMS. If for example I want 2MB then
Bank0: (4) 256K x 9
Bank1: (4) 256K x 9

So I need 8 x 256K 9 chip 30 pin SIMMS?
I've seen a few photos of the motherboard with 3 chip SIMMS? Will either work or does it have to be 9 chip?

I might also go 4MB which might be more cost effective?
(4) 1M x 9

It

No, you don't need 8x256KB.
9 chips have better compatibility, but I never had issues with 3, not a reliable source though.

If Ram configuration table is correct you can mount up to 64MB.
4x1MB is better.
In time you can buy more, with some luck, at a good price.

Thanks for the info. Trying to remember all this info from almost 40 years ago 😀

Off to find some chips.

With 128 KB of L2 cache, I recommend to use 4, 5 or 8 MB of RAM.
The cacheable area of a 386DX/486 with 128 kB cache size is 16 MB.

386DX40 deserves 8MB RAM. May protected mode games require that and windows 3.1 is faster as well. 16MB RAM isn't that useful as the software usually requires a faster CPU as well. 16MB is more suitable for a 486DX2/66.

OS/2 loves to work with RAM, on about any system. 🙂

~6 to 8MB was the lower minimum that the developers had recommended (for OS/2 of early 90s).

It often was being bundled with 4 MB PCs, though, which it struggled with (like Win 95 did).

About 12 MB onwards made it run smooth, I believe.

Edit: Windows for Workgroups is similar, maybe, if all the networking features are enabled.
The sharing of resources (printer, files) is memory taxing, too.
I remember reading about WfW mail servers in offices being run on fast 486 PCs with lots of RAM (up to 24 MB).
There was a picture of such a server hidden in a closet.