From the SiS 496-497 datasheet: ftp://retronn.de/docs/chipset/SiS%20496-497.pdf
"1.1 DRAM Controller
Supports 8 Banks Non-Interleaved Access for Single and Double Sided SIMMs up to 255 MBytes.
Supports DRAM CAS Before RAS Refresh.
Supports "Table-Free" DRAM configuration.
Programmable driving current for the DRAM signals.
Supports Symmetrical and Asymmetrical DRAMs.
Supports 256K/512K/1M/2M/4M/8M/16M/32M xN Fast Page Mode and EDO DRAM.

1.2.3 DRAM Memory Operations
The 85C496 can support 8 rows (banks) of DRAM, and memory size from 1 MBytes up to 255 MBytes. Each bank could be single or double sided 32 bits Fast Page Mode or Extended Data-Out DRAM. The installed DRAM type can be 256K/512K x 36, 1M/2M x 36 or 4M/8M/16M/32M x 36 SIMMs."

So max ram per slot(?) is 32M and FPM Parity (x 36) appears to be recommended. You cannot use 128Mb 72pin as the chipset has a 32Mb max per slot which explains why it only see's 32Mb of each 128Mb simm. Always check data sheets if possible because motherboard manuals are not always accurately written...

added: I think the terms bank and slot are the confusing part. I have a gut feeling that your board might have a max of 128MB, 32mb per bank x 8 max banks yields 256M but the board has 4 banks so the max could be only 128Mb.

peg wrote on 2020-02-18, 06:10:

Hi, Been lurking for a long time and finally decided to post a question to the glorious users of Vogons. I'm trying to "max out […]
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Hi,
Been lurking for a long time and finally decided to post a question to the glorious users of Vogons. I'm trying to "max out" or at least fill my 486 motherboard with as much memory as possible and I'm running into problems.

My hardware is:
M-tech R418W2, Award bios REV: Kw
CPU: Cyrix 5x86 120
No hard drive or any other devices as of yet

Anyway, my issue is this motherboard just basically refuses to properly recognize the memory I put into it . This board has 8 30 pin simms and 2 72 pin simms, supposedly you can mix them and the one or two manuals I've found online say that you can. The "max amount" of RAM is supposedly 256 meg (8 x 16 meg 30 pin and 2 x 64 72 pin simms).

I can't even load any 72 pin simms unless I load 4 megs of 30 pin simms in one of the slots. If I don't load any 30 pin simms, it flat out wont recognize the 72 pin simms at all. And when it does accept my 72 pin simms, it always recognizes them at 1/4 of the value they should be (very weird). So for 72 pin, I put a 64 MB simm and it only says 16, 128 MB simm and it only reads it as 32 (even though this board supposedly doesn't even support 128 meg simms). It wont boot period if I use EDO ram as far as I can tell.

The max amount of RAM I've successfully been able to POST with is 84 MB:
4x1 MB 30 pin (4 MB)
4x4 MB 30 pin (16 MB)
2x128 MB 72 pin = (recognized as 64 MB)

Anyway, does anyone have experience with this board? Is there a bios setting or jumper or something I'm missing here? I 'v tried so many different 30 pin and 72 pinn simms combinations and it always gives me the same weird issues with only recognizing 1/4 the size of the 72 pinn simms.

Thanks!

Hey man,

Which version of the board do you have? There are two. One has the SMC I/O chip and the other has the Winbond I/O chip. The I/O chip sits right behind the PCI slots. I had a bunch of these at one time. Since you say you have the KW BIOS revision that should be the Winbond I/O chip on yours. Very nice 486 board BTW.

Thanks for the responses! I have the version with the winbond chip and the award bios. It also says R418-B in the corner of the PCB next to the bottom ISA slot. The sticker on the board just says "R418W2". I'm beginning to wonder if it is really 128 max since I've never been able to get more than 32MB in a 72 pinn simm, despite using several different 64 and even 128 MB simms. What's wierd about that is the "manual" I've been looking at doesn't even show 32MB simms or 4x8MB 30 pinn simms as an option. I've also been entirely unsuccessful getting any sort of EDO ram to work on it.

I have 64MB on mine. Two 32MB 72-pin. Almost overkill for a 486 IMO. So I never tested beyond that.

I've yet to be able to get more than 16MB (4MB x 4 simms) out of a 30 pin "bank" and 32MB in a 72 pin slot. Thus I'm led to believe the max capacity of this motherboard is actually 96MB instead of the alleged 256.

Also, does anyone know what the max cacheable RAM for this chipset (SIS 496/497) is anyway?

It claims 1MB. Check my links from this older post.

Re: The great Pentium Pro haul of 2018

Tried some more RAM, still have issues. I tried plugging in 64MB of 30 pin simms and it just shows up as 16MB (1/4 of what it should be). Won't even let me add 72 pin simms under that configuration. I'm now led to believe that the "manual" for this MB is complete BS, and that the true limit for this thing is 96MB, a far cry from the supposed 256MB. Maybe there is some newer bios version out there that I'm missing? As far as I can tell, I have the most current BIOS of the ones that have been dumped.

Does anyone else have this board and tried different memory configurations?

Horun wrote on 2020-02-19, 02:27:

From the SiS 496-497 datasheet: ftp://retronn.de/docs/chipset/SiS%20496-497.pdf "1.1 DRAM Controller Supports 8 Banks Non-Inter […]
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From the SiS 496-497 datasheet: ftp://retronn.de/docs/chipset/SiS%20496-497.pdf
"1.1 DRAM Controller
Supports 8 Banks Non-Interleaved Access for Single and Double Sided SIMMs up to 255 MBytes.
Supports DRAM CAS Before RAS Refresh.
Supports "Table-Free" DRAM configuration.
Programmable driving current for the DRAM signals.
Supports Symmetrical and Asymmetrical DRAMs.
Supports 256K/512K/1M/2M/4M/8M/16M/32M xN Fast Page Mode and EDO DRAM.

1.2.3 DRAM Memory Operations
The 85C496 can support 8 rows (banks) of DRAM, and memory size from 1 MBytes up to 255 MBytes. Each bank could be single or double sided 32 bits Fast Page Mode or Extended Data-Out DRAM. The installed DRAM type can be 256K/512K x 36, 1M/2M x 36 or 4M/8M/16M/32M x 36 SIMMs."

So max ram per slot(?) is 32M and FPM Parity (x 36) appears to be recommended. You cannot use 128Mb 72pin as the chipset has a 32Mb max per slot which explains why it only see's 32Mb of each 128Mb simm. Always check data sheets if possible because motherboard manuals are not always accurately written...

added: I think the terms bank and slot are the confusing part. I have a gut feeling that your board might have a max of 128MB, 32mb per bank x 8 max banks yields 256M but the board has 4 banks so the max could be only 128Mb.

There's more confusing stuff:

A bank is NOT a slot. A bank is a logical (not physical) organisation of RAM with (in the case of a 486) 32 data lines. A single-sided SIMM fills one bank, a double-sided SIMM fills two banks. So 8 banks means max four double-sided SIMMs. Note that "single-sided" and "double-sided" refer - again - to logical organisation, not physical build. Single-sided has 32 data lines, regardless of where the chips physically are (generally on one side, but not always), double-sided has 64 data lines, regardless of where the chips are physically (generally but not always on two sides). So you need to look at individual chips.

And then focusing on chips: those 4M/8M/16M/32M are chip densities, measured in Mbit (NOT MByte). Total width of a bank is 32b (or 36b with parity, but ignore that for simplicity), so max total bank is 32Mx32=1024Mbit=128MByte. That means that 256MB total should be possible with either single or double sided 128MB SIMMs. *BUT* the chips may be max 32M, so assuming 8 chips, so 4 data lines each, you can have 32Mx4 chips, so max 16MB per chip. If your SIMMs have higher densities than 32M, only part of each chip will be recognized.

But... this is what the chipset can handle. Bad implementation on the motherboard can limit it further. I know I have run 486 motherboards with iirc SiS496 chipset with 2x128MB (16 16Mx4 chips each) in the past. I used it with a PODP-83 and installed Windows XP. Because I could 😜 - but that doesn't guarantee that any SiS496 board will be able to do the same.

dionb wrote on 2020-02-24, 10:01:

There's more confusing stuff:

A bank is NOT a slot. A bank is a logical (not physical) organisation of RAM with (in the case of a 486) 32 data lines. A single-sided SIMM fills one bank, a double-sided SIMM fills two banks. So 8 banks means max four double-sided SIMMs. Note that "single-sided" and "double-sided" refer - again - to logical organisation, not physical build. Single-sided has 32 data lines, regardless of where the chips physically are (generally on one side, but not always), double-sided has 64 data lines, regardless of where the chips are physically (generally but not always on two sides). So you need to look at individual chips.

I agree !

dionb wrote on 2020-02-24, 10:01:

And then focusing on chips: those 4M/8M/16M/32M are chip densities, measured in Mbit (NOT MByte).

I disagree ! in section 1.1 they state: Supports 256K/512K/1M/2M/4M/8M/16M/32M xN Fast Page Mode and EDO DRAM.
In first line section 1.2.3: The 85C496 can support 8 rows (banks) of DRAM, and memory size from 1 MBytes up to 255 MBytes
In the same section 1.2.3 third line they state: The installed DRAM type can be 256K/512K x 36, 1M/2M x 36 or 4M/8M/16M/32M x 36 SIMMs."
Sort of a repeat of section 1.1 and I do not see anywhere they shift from the term Mbytes to Mbits, so they are still using Mbytes.

dionb wrote on 2020-02-24, 10:01:

But... this is what the chipset can handle. Bad implementation on the motherboard can limit it further. I know I have run 486 motherboards with iirc SiS496 chipset with 2x128MB (16 16Mx4 chips each) in the past. I used it with a PODP-83 and installed Windows XP. Because I could 😜 - but that doesn't guarantee that any SiS496 board will be able to do the same.

You should have taken pictures ! That may never happen again 😁

So I'm still trying more RAM on this thing, I've now successfully booted it with 96MB using 8x4MB 30 pin simms, and 2x32MB 72 pin simms, all of it 60ns, FPM with parity. Oddly, it hangs on the memory test if I don't put the 30 pin RAM in there and just try 2x32=64MB 72 pin simms. I wonder if non-parity would make any difference?

Horun wrote on 2020-02-25, 06:00:

[...] […]
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[...]

dionb wrote on 2020-02-24, 10:01:

And then focusing on chips: those 4M/8M/16M/32M are chip densities, measured in Mbit (NOT MByte).

I disagree ! in section 1.1 they state: Supports 256K/512K/1M/2M/4M/8M/16M/32M xN Fast Page Mode and EDO DRAM.
In first line section 1.2.3: The 85C496 can support 8 rows (banks) of DRAM, and memory size from 1 MBytes up to 255 MBytes
In the same section 1.2.3 third line they state: The installed DRAM type can be 256K/512K x 36, 1M/2M x 36 or 4M/8M/16M/32M x 36 SIMMs."
Sort of a repeat of section 1.1 and I do not see anywhere they shift from the term Mbytes to Mbits, so they are still using Mbytes.

On the contrary, they are explicitly talking about chip densities:

https://www.oreilly.com/library/view/pc-hardw … ch05s04s02.html

Chip Density

Memory modules are constructed from individual memory chips, which vary in their capacity. Chip capacities are specified in megabits (Mb or Mbit) rather than megabytes (MB). Because there are eight bits per byte, a memory module that uses eight chips can store the number of megabytes specified by the megabit size of the chip. For example, a memory module that uses eight 128-Mbit chips is a 128 MB memory module.

Chipsets don't talk to DIMMs but to banks of DRAM. A bank is 32 (non-parity) or 36 (parity) bits wide. 32Mx32b=1024Mb=128MB, as I stated. I can guarantee that 32MB (256Mb)x32=1024MB SIMMs will not work with this chipset 😮

peg wrote on 2020-02-25, 08:02:

So I'm still trying more RAM on this thing, I've now successfully booted it with 96MB using 8x4MB 30 pin simms, and 2x32MB 72 pin simms, all of it 60ns, FPM with parity. Oddly, it hangs on the memory test if I don't put the 30 pin RAM in there and just try 2x32=64MB 72 pin simms. I wonder if non-parity would make any difference?

Odd you cannot get 32MB in each 30pin bank. Maybe they ran the address lines different to those than the 72pin. You can try non parity, check the BIOS first and disable anything that says something similar to "Parity check" before changing out the ram.

I would try that except I do not believe that 8MB 30 pin simms exist, or if they do, they are exceptionally rare. I did try 16MB FPM/Parity simms (4.x16=64MB in a bank) off ebay and they did not work.

Horun wrote on 2020-02-25, 22:32:

peg wrote on 2020-02-25, 08:02:

So I'm still trying more RAM on this thing, I've now successfully booted it with 96MB using 8x4MB 30 pin simms, and 2x32MB 72 pin simms, all of it 60ns, FPM with parity. Oddly, it hangs on the memory test if I don't put the 30 pin RAM in there and just try 2x32=64MB 72 pin simms. I wonder if non-parity would make any difference?

Odd you cannot get 32MB in each 30pin bank. Maybe they ran the address lines different to those than the 72pin. You can try non parity, check the BIOS first and disable anything that says something similar to "Parity check" before changing out the ram.

dionb wrote on 2020-02-25, 16:05:

Chipsets don't talk to DIMMs but to banks of DRAM. A bank is 32 (non-parity) or 36 (parity) bits wide. 32Mx32b=1024Mb=128MB, as I stated. I can guarantee that 32MB (256Mb)x32=1024MB SIMMs will not work with this chipset 😮

Agree that chipsets talk to banks of ram. Under that "Chip Density" topic on that specific webpage he gives an example:
"However, you must not install memory that uses higher-capacity chips than your chipset supports. For example, the Intel 815 chipset supports 16-, 64-, 128-, and 256-Mbit chips, so an 815-based motherboard could use either the eight-chip or the 16-chip, 256 MB DIMM. "
256Mbit chips x 8 chips per DIMM then divided by 8 for Bits to Bytes conversion for 256MB(MBytes).

Found a few BIOS for the board but does not address anything memory related in it's description...