1) Can i combine RAM sticks with different sizes ? I'd like to buy one 8MB module so I'd have 12 MBs in total.

That is quite literally what the table you posted says you can do, and it even tells you which SIMM to put in which slot.

486 have a 32b wide bus and 72p SIMMs are 32b wide, so a single SIMM forms a bank and two different banks need not be similar. It's different with most Pentium chipsets as the Pentium has a 64b wide bus so you need to install 72p SIMMs as pairs that need to be identical.

I read about EDO and FPM types - i don't recall those abbreviations from my childhood. Which one do i need to order so it gets along with my current RAM module?

That suggests your childhood was prior to the introduction of EDO 😉

In general, 486 chipsets don't support EDO and on those that do, performance gain is limited. If you insert EDO SIMMs into unsupporting boards, either they will not be recognized or - more common - the system will fail to boot with a RAM error. The SIMM you have is FP ("4400" in the chip name is indicative of 4Mb FP chips, 8 of them give you a 4MB SIMM). So get a SIMM with sixteen of the same chips and you should have 8MB, for 12MB total.

According to the table, you can combine any modules of different supported sizes in any order.
Your module is FPM (chips partname ends with zero: 4400)

Vaylo wrote on 2024-01-30, 08:29:

So i'm looking at my current RAM module sitting in my newly acquired 486 - the sticker reads Legend and there are 8 Alliance AS4 […]
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So i'm looking at my current RAM module sitting in my newly acquired 486 - the sticker reads Legend and there are 8 Alliance AS4C14400 chips. Memory test shows i have 4096kB of RAM. Manual to my mobo (zida tomato 4dps 2.11) says it supports the following :

The system board supports flexible SIMM configuration:
· Flexible memory bank location and size.
· Accept 2 pieces of 72-pin SIMM sockets, SIMM 1/ 2, total 2 banks.
· Support SIMM type: 1Mx36, 2Mx36, 4Mx36.

This is what i have:

Since it's been 30 years already since i was fiddling with these systems i don't recall all the do's and don'ts so please help me a little here.

1) Can i combine RAM sticks with different sizes ? I'd like to buy one 8MB module so I'd have 12 MBs in total.
2) I read about EDO and FPM types - i don't recall those abbreviations from my childhood. Which one do i need to order so it gets along with my current RAM module?

Thanks in advance, i'm sure i will have more questions 😀

Yes, stick to FPM, EDO might work, but it is unlikely and not worth the trouble.
It is hard to believe that 32MB is the maximum for this board.
I would expect that at least 2 times 32MB (those are normally double sided) for a total of 64MB should be supported.
The Asus PVI (same chipset, also only 2 Simm slots) even supports 2 times 64MB for a total of 128MB, but finding the right 64MB modules for a 486 board is tricky.

If it were me I would get one 16Mb simm, for total 20Mb, which is in the chart. Only because I like keeping single sided with single sided if possible...have seen less quirks that way 😀

Looks a lot like my POD build.

It maxes out at 32mb but only if you use two double sided 16mb sticks it won’t support a single 32mb, at least not as a full 32mb

The bus does support single sticks, so matched isn’t required

Maybe i'm dumb to understand these instructions but this time i need help with a Pentium machine, mobo manual shows this:

If i aim for 64MBs of RAM seems the only way how to achieve it is to fill all 4 slots with 16MB modules? Using 2x32MB in just one bank will not work?

Thanks.

Odd table... it shows support for two double-sided 8MB SIMMs and for four 32MB and 128MB SIMMS , but then neglects to mention support for two 32MB double-sided SIMMs. That "*32" notation is also highly confusing and I don't blame you for not being sure what it's trying to tell you.

I'd be highly surprised if it wouldn't work with two 32MB EDO SIMMs given it does explicitly say you can use four of them to get 128MB, and two is technically less challenging than four. Only thing that could prevent it working is some brain-dead BIOS programmed to only allow what this table shows. Highly unlikely though. This looks like a generic board with i430HX chipset which should have no trouble at all with the config you want to use.

Basically you should not exceed the cacheable area with your amount of RAM.
To avoid a performance drop you should not exceed 32 MB RAM in total when you have 256 kB of L2 cache operating in write-back mode.

In a Pentium machine RAM width is double, so you need two 72-pin modules. Your cacheable area is doubled too, e.g. with 256 kB cache 64 MB RAM.

Vaylo wrote on 2024-04-20, 09:38:

Maybe i'm dumb to understand these instructions but this time i need help with a Pentium machine, mobo manual shows this: […]
Show full quote

Maybe i'm dumb to understand these instructions but this time i need help with a Pentium machine, mobo manual shows this:

If i aim for 64MBs of RAM seems the only way how to achieve it is to fill all 4 slots with 16MB modules? Using 2x32MB in just one bank will not work?

Thanks.

That mobo should support two 32 mb sticks.

Looks like it maxes out at 512mb which is about as big as popular end user simm setups got. Servers could do more.

What mobo? Many of those era were happiest at 64mb because of caching issues, but not all were affected and could go to 512mb without much slow down

Thank you guys for your help and comments.
I just found this website:
https://stason.org/TULARC/pc/motherboards/Z/Z … X-VER-1-20.html

They say that the following combination (among many others) is indeed possible:

Size Bank 0 Bank 1
64MB (2) 8M x 36 none

Looks like they are describing it as:

4mBIT x 32bit wide

etc. (or, [[4096 / 8 ] /32] = 16)

16mb modules.

4x 16mbyte modules == 64mbyte

(shrug)

Vaylo wrote on 2024-04-21, 06:59:

Thank you guys for your help and comments. I just found this website: https://stason.org/TULARC/pc/motherboards/Z/Z … X-VER-1- […]
Show full quote

Thank you guys for your help and comments.
I just found this website:
https://stason.org/TULARC/pc/motherboards/Z/Z … X-VER-1-20.html

They say that the following combination (among many others) is indeed possible:

Size Bank 0 Bank 1
64MB (2) 8M x 36 none

Ah, good old TH99 😉

There's a more modern community-supported version now https://theretroweb.com/ , for motherboards I'd recommend it over the (ancient, not always reliable and definitely not up to date) original. Only benefit of TH99 over the Retroweb is that more device types are described there - it's still the best out there for obscure old I/O cards.

Link for this board specifically:
https://theretroweb.com/motherboards/s/zida-5dhx-ver.-1.20

Regarding the comment above on cacheable area: that's always good advice. For the i430HX chipset, the cacheable limit is 64MB with one 8b tag RAM, or 512MB with two. If you go over that, there's no L2 caching for RAM above it, and irritatingly most OS stuff starts using RAM from the top, i.e. the uncached bit, so it impacts everything. So only exceed the cacheable limit if the alternative is thrashing to HDD (which is vastly slower than - even uncached - memory access). 64MB is a good sweet spot for Windows 95 on a system like this. DOS would be happy with 1/4 that (and indeed 16MB would give less problems with games incorrectly autodetecting RAM as too small, as tends to happen over 16MB), Win98 might like more, but tbh this system will be a slug with Win98 applications anyway, so just don't do that 😉

Since multiple motherboards are talked about in this thread let it be known, 486 you need one 72 pin simm or 4 30 pin simms to complete the bus width

With pentium eg socket 4, 5, 7, ss7
You need 1 dimm, two 72 pin simm, or 8 30 pin simm to populate the bus width

Note:
If I recall correctly, there are some early 486 motherboards that had 16 bit busses though? So 2 30 pin simms

Commenting specifically on that board that was linked above,

Agreed,

Unless you are using a k6-3, K6-2+, K6-3+ just stick to 64 MB of ram, unless you want to try to modify the motherboard for dual tag.

If you do have one of the mansioned processors, then go ham all the way up to 512 if you want

Thank you all for your comments.

I will need the additional RAM for a Pentium 1 system running @ 166 Mhz. Currently there are 4 x 8MBs modules but as i have Windows 98 installed you can imagine it's a bit of pain with just 32MB. Based on your feedback I'm gonna replace all 4 modules with two 32MB SIMMs .

Edit: Now that i think of it....i can leave two 8MB modules there so there would be 32 + 32 + 8 + 8 = 80MBs in total. Do you see any issues with such a non-standard combo?

Vaylo wrote on 2024-04-21, 16:27:

Edit: Now that i think of it....i can leave two 8MB modules there so there would be 32 + 32 + 8 + 8 = 80MBs in total. Do you see any issues with such a non-standard combo?

The mainboard will happily work with 80MB. The Intel 430 series is very flexible about memory addressing and does not prescribe specific module combinations or ordering. On the other hand, unless your mainboard has specific provisions to enlarge the cacheable area of the L2 cache (which is typically only present on semi-pro or pro grade boards, but not on regular consumer boards, and also exclusive to the 430HX chipset), having RAM in excess of 64MB can noticably degrade system performance. You can try what works better for you (the last 16 MB uncached is clearly better than a constantly swapping system), but general advice is to not exceed the cacheable area in normal circumstances, especially if the total memory gain is just 25% (64MB comprated to 80 MB).

CoffeeOne wrote on 2024-01-30, 20:35:

Yes, stick to FPM, EDO might work, but it is unlikely and not worth the trouble. It is hard to believe that 32MB is the maximum […]
Show full quote

Vaylo wrote on 2024-01-30, 08:29:

So i'm looking at my current RAM module sitting in my newly acquired 486 - the sticker reads Legend and there are 8 Alliance AS4 […]
Show full quote

So i'm looking at my current RAM module sitting in my newly acquired 486 - the sticker reads Legend and there are 8 Alliance AS4C14400 chips. Memory test shows i have 4096kB of RAM. Manual to my mobo (zida tomato 4dps 2.11) says it supports the following :

The system board supports flexible SIMM configuration:
· Flexible memory bank location and size.
· Accept 2 pieces of 72-pin SIMM sockets, SIMM 1/ 2, total 2 banks.
· Support SIMM type: 1Mx36, 2Mx36, 4Mx36.

This is what i have:

Since it's been 30 years already since i was fiddling with these systems i don't recall all the do's and don'ts so please help me a little here.

1) Can i combine RAM sticks with different sizes ? I'd like to buy one 8MB module so I'd have 12 MBs in total.
2) I read about EDO and FPM types - i don't recall those abbreviations from my childhood. Which one do i need to order so it gets along with my current RAM module?

Thanks in advance, i'm sure i will have more questions 😀

Yes, stick to FPM, EDO might work, but it is unlikely and not worth the trouble.
It is hard to believe that 32MB is the maximum for this board.
I would expect that at least 2 times 32MB (those are normally double sided) for a total of 64MB should be supported.
The Asus PVI (same chipset, also only 2 Simm slots) even supports 2 times 64MB for a total of 128MB, but finding the right 64MB modules for a 486 board is tricky.

You would be amazed how many name brand systems even into early 1997 had extremely limited ram expansion listed in the documentation.

I never could understand why that was a thing