While EDO chips on 30-pin RAM sticks do exists, they were never used in common PC systems. So FPM is the correct memory type for 286 / 386 / 486 boards with 30-pin sockets. All 486 boards support 1MB and 4MB sticks (i.e. banks of 4MB or 16MB). A few also support 16MB sticks, but they are not worth the price except for novelty value. (You have a board that supports those, and want to pose with a 486 board with 128MB RAM on 30-pin sticks? Go get those modules, it's cheaper than posing with a Tesla Model S...)

Mixing sticks from different manufacturers is no issue most of the time. Faster access time is no issue in all practical cases. Most consumer 486 boards work fine with parity check disabled, or auto-detect whether the modules provide parity and auto-disable parity checking on non-parity modules. Don't mix parity and non-parity modules if you can't manually disable parity checking. Random bit corruption is rare, and no issue for retro fun with games, so no need for parity with that. On the other hand, RAM getting unreliable can happen, and getting parity errors as hint that the RAM is the cause for the sporadic crashes you observe might help troubleshooting a lot. So parity isn't required, but it still has some marginal value.

lavadrop wrote on 2022-04-19, 17:57:

Unfortunately, my Gemlight GMB-486UNP only recognizes 3 of the 4 sticks of RAM I have

wait, how do you know? after all it requires minimum of 4 fitted to operate

rasz_pl wrote on 2022-04-19, 23:31:

lavadrop wrote on 2022-04-19, 17:57:

Unfortunately, my Gemlight GMB-486UNP only recognizes 3 of the 4 sticks of RAM I have

wait, how do you know? after all it requires minimum of 4 fitted to operate

That's correct, your motherboard needs to have 4 matched set of memory per bank, get another matched set of 4 x 1MB or 4 x 4MB, either 60ns or 70ns all FPM. Only non-parity OR parity.
Go with non-parity for now.

Cheers,

lavadrop wrote on 2022-04-19, 17:57:

The manual does not state which kind of memory it takes.

That's because there's pretty much only one type for that era and board.
The type that every second user here has rotting away by the dozen in some cardboard box.
30 pin SIMM.

Get two sets of four SIMMs of one MB each, for around eight bucks, like these:
https://www.ebay.de/itm/4-x-1MB-SIMM-Module-R … r-/294781913307
https://www.ebay.de/itm/4x-1MB-Simm-RAM-30-pi … B-/165285761446
https://www.ebay.de/itm/4-x-1MB-SIMM-Module-R … r-/294861832968

The 486 chip has a 32 bit memory bus and 30 pin SIMMS are only 8 bit each. Four of them form a 'bank' and need to be completely synchronous. So, mixing different ones in one bank is asking for trouble.
Nothing against using four of the one and four more of the other type.

Leave the 4 MB modules for systems that actually make use of them and spend the money on something else that you would notice during use, like better VGA, or ice cream.

Cheers!

rasz_pl wrote on 2022-04-19, 23:31:

lavadrop wrote on 2022-04-19, 17:57:

Unfortunately, my Gemlight GMB-486UNP only recognizes 3 of the 4 sticks of RAM I have

wait, how do you know? after all it requires minimum of 4 fitted to operate

The 4-1Mb modules are in bank 0, but BIOS memory test only counts 3,072 Mb.

Alright, thank you for the answers, now I feel reassured that I can mix sticks with the same specs.

lavadrop wrote on 2022-04-20, 17:15:

rasz_pl wrote on 2022-04-19, 23:31:

lavadrop wrote on 2022-04-19, 17:57:

Unfortunately, my Gemlight GMB-486UNP only recognizes 3 of the 4 sticks of RAM I have

wait, how do you know? after all it requires minimum of 4 fitted to operate

The 4-1Mb modules are in bank 0, but BIOS memory test only counts 3,072 Mb.

To be correct here: Horses have been known to vomit, but - the systems is supposed to work with all four or not at all. So, that's at least strange.
Anyway, no one bothers with 4 to 8 MB problems. Those things are "just there".

lavadrop wrote on 2022-04-20, 17:15:

rasz_pl wrote on 2022-04-19, 23:31:

lavadrop wrote on 2022-04-19, 17:57:

Unfortunately, my Gemlight GMB-486UNP only recognizes 3 of the 4 sticks of RAM I have

wait, how do you know? after all it requires minimum of 4 fitted to operate

The 4-1Mb modules are in bank 0, but BIOS memory test only counts 3,072 Mb.

the rest is most likely reserved for something, there is 99.99% no way for 486 board to run with only 24 data bit of ram available.

rasz_pl wrote on 2022-04-21, 03:43:

lavadrop wrote on 2022-04-20, 17:15:

rasz_pl wrote on 2022-04-19, 23:31:

wait, how do you know? after all it requires minimum of 4 fitted to operate

The 4-1Mb modules are in bank 0, but BIOS memory test only counts 3,072 Mb.

the rest is most likely reserved for something, there is 99.99% no way for 486 board to run with only 24 data bit of ram available.

Nothing is reserved, I don't have any OS installed, not even a hard disk connected, it's just the BIOS memory test reporting 3,072 kb (I just realized I wrote 3 Gb 😁 )

reserved by bios itself
30 pin simms have no mechanism of reporting capacity like 72pin ones (jumpers) or dimms (SPD eprom), so bios test routine counts available ram by reading back what it wrote.

are you sure its not saying:

640 KB base memory
3072 KB extended memory

I have to get back on you about the exact screen of the AMI BIOS memory test.
However, the sums don't make up for all the RAM.
IIRC, my original Compaq Presario 486SX had 4,096 total RAM-4 sticks. Then my mother bought me 4 more (when Rebel Assault 2 came out) for a total of 8,192 KB.
This one has 4 sticks, that should be 4096 KB. If you subtract the 640 KB, it should be 3,456 Kb. Now, 3,072 + 640 KB is 3,712 KB, still missing 384 KB.

reserved by bios itself

You are right, I haven't any experience with BIOS shadowing and it's enabled on my board. That explains why the system reports 3,712 kb RAM only.
Thank you.