Old Pentium 166 MMX RAM question...

[gyoung]

I've been trying to upgrade the memory on my fiance's PC. She has a IBM Aptiva 2161/C85.

I've looked up the model on IBM's website and I've read the manual up and down. It says that it takes EDO or SDRAM. It can take a maximum of 64MB. I opened up the box and there is 1 32MB DIMM in the slot. I want to add another 32MB to max out her RAM and give her a little performance boost.

As a test I slid in a spare stick of a 64MB DIMM that I had lying around. This was a PC133 stick. When it booted up, the post screen showed 48MB of RAM installed. So I went to Best Buy and bought a 32MB stick of Kingston ValueRAM for $25. When I installed this RAM it showed only 40MB of RAM in the post screen. What gives?

I did notice this:

The 64MB stick has a density of 8Mx16 (4 chips on one side of the DIMM).

The 32MB Kingston stick has a density of 4Mx64 (4 chips on one side of the DIMM).

The 32MB stick that was in the computer had 4Mx64 (8 chips on both sides of the DIMM for 16 total chips).

Any ideas? Does it not like single sided DIMMS. I've been to crucials website and other RAM websites and they always quote a very high price for the RAM. Is this because I would be buying the more expensive and more rare 32MB double sided dimm?

[justy]

Not familiar with that board, but is it possible that it requires parity sticks?
Therefore only seeing enough of the actual ram, minus the parity?

Just a thought, could be way off.

All the best, Justy.

[kfaulkne]

Try putting memory in different slots or bios update.

[Nighthawk]

I have worked with both dual-sided and single-sided 32MB SIMMs on older boards. It looks to me that the 430TX board is the first one to support single-sided DIMMs. If you put a single-sided 4-chip DIMM into a VX or earler board, it will POST at 8MB, which is where your 40 MB comes from (32+8). The density is the same with a single-sided 64MB, but it will POST at 16MB (32+16=48). Your problem is that you are using high-density DIMMs in an incompatible board.

You need to get the double-sided, 16-chip DIMMs that are worth 32MB.

[gyoung]

Anyone know a good site for BIOes for old motherboards? I've been to IBM website (the computer is an IBM), but it doesn't display any info about the changes that are included in the bios.

Thanks!

[gyoung]

Found this information, this solves my problem. I'll have to try my luck on ebay or in the traders forums.

The Intel VX doesn't have enough Memory Address lines to drive the higher integration DRAM technology, be it EDO or SDRAM. 16-MBit is the highest density supported, while the parts on a 64-MByte EDO SIMM are 64-MBit (eight chips)

Do the math - count the SDRAM chips on your DIMM (the large ones) [if they're ECC DIMMs, round down to the nearest power of two], and compute:

((total capacity in MByte)*8)/(number of chips)

The result is the density in MBit of the SDRAM components used.

Examples:

32-MByte DIMM with 16 chips: 32*8/16=16, usable with Intel VX.

128-MByte ECC DIMM with 18 chips - round down to 16, 128*8/16 = 64, not usable on VX.

As current production is 64- or 128-MBit densities, the bottom line of all this is that SDRAM support in Intel VX is useless with today's DIMMs.

Also, in order to have your board recognize 32Mb per DIMM, you'll need the 16-chip versions. If you have the 8-chip version, only 8Mb (your case) will be recognized.

Remember, it's not a memory problem; it's a chipset limitation. And no, this can't be fixed by a BIOS update.