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Upgrading RAM

I currently have two machines each with 2 * 16 Mb 72
pin EDO RAM. (i.e. each has a total of 32Mb RAM).
 The two sets of RAM are obviously made by different                                manufacturers. (i.e. one pair has chips on both sides of                                  the module, and the other pair has chips on one side                                  only.)                                  I had heard that you shouldn't mix RAM from different  manufacturers even if they are the same type. Anyway, as
an experiment I put the four sticks of RAM in one
 machine to make 64 Mb. The machine certainly worked
 faster. The only problem I noticed was that almost every
  time I closed an application (browsers, word, excel etc) I
 get a "This program has performed an illegal operation",
  message. Although, I seem to be getting that a fair bit
 even with 32Mb RAM since I installed Windows98 SE
 the other day. ?
 I'd like to run one machine with this combination of 64Mb
 RAM and put some old Fast Page RAM (2*8), that I
  have spare, in the other machine,(+ another 2*8 FP RAM that I'll need to buy) to make 32Mb RAM in the  second machine.
The main point I'm getting at is: is it O.K. to just bung in extra banks of RAM like this assumming it's the same  type BUT from different manufacturers?
 As you'd be aware it's difficult to find out who made your RAM (at leastI think it is), and even harder to find exactly   the same type especially if it's a few years old.
 I don't really want to start all over again and buy new  banks of 64Mb(EDO) for one machine and 32 Mb (FP)  for the other. I'm hoping I can just combine the two 32's  and just buy 2*8 Fast Page to add to the 2*8 Fast Page that I have spare.
 Any comments or thoughts would be greatly appreciated.
 Hope I have explained the problem clearly.
1 Solution
If you get the same errors with 64Mb as with 32Mb, sounds like your install is a bit screwy, or that the 32Mb had problems to start with.
First, are you sure that they are both EDO ram and that they are both the same speed? Are both sets either parity or non-parity?

The good news is that while odd chips can sometimes be a pain to mix, 2 matched pairs, of different manufacture, often will work perfectly well together, provided they are of a similar type or that the motherboard is comfortable running to suit the specs of the lowest spec pair.

Some machines will give you problems with trying to put 2 pairs of 8mb SIMMs in. This is because there may not be enough banks of memory to allocate to them. An 8mb 72 pin SIMM is electrically double sided, it has two banks of RAM on one module, the system sees it as 2 4mb SIMMs. The terminology gets confusing here depending on whether the motherboard manufacturer decides to call a bank 32 or 64 bits wide in the manual. I am talking 32 bits. A lot of motherboards with 4x72pin SIMM slots and some with 6, have only 6 memory banks to allocate. Each 8mb SIMM is two banks, so putting two in takes 4 banks, that leaves 2 banks, now putting another 2 8mb SIMMs in may mean (in a 6 bank board) that only half of each SIMM will be seen, because only one bank is left to be allocated to each of the remaining SIMM sockets (for a 4 socket board) only the first 4mb bank of each 8mb may be seen. That would only give you a total of 24Mb Ram instead of the 32Mb you were expecting. Some people insist at this point that "one SIMM is dead" and come up with all sorts of reasons why it is one and not the other. If one was dead, neither would be seen by the system.

16Mb SIMMs do not have this problem. they are single sided (electrically). I have a suspicion that the one with the chips on the back that you have has parity chips on the back. If the other has no parity, disable any parity check options by jumper on the motherboard and in the BIOS.

Other "double sided" or double banked sizes of SIMM are, 2Mb, 8Mb, 32Mb. It is dependant on the address lines used.

So, best thing to do would be to see if you can borrow a couple of 8mbs first, just to see if they will work at full capacity. Or to read over your motherboard manual (post motherboard manufacturer and model and preferably bios ID string here to get a downloadable one) and see what configurations that recommends and how many banks it says it has. If it does not say the number of banks, and doesn't list a likely configuration, look and see if there is a configuration that uses 4xdouble banked SIMMs, if not, then it probably can't. If it turns out you can't use more 8mbs, then you can probably find someone to give you a couple of 4mbs for 24Mb total, or you have to fork out your "hard earned" for 2x16mb.

If both motherboards are equal in performance but different manufacturers or chipsets, maybe one will work and the other won't. Of course you may have to swap the faster CPU over too.


Road Warrior

This sounds a bit too simple, but give it a try....
Take out your RAM and put it on a static free surface.  Take a pencil eraser and run it across the contacts of each RAM module.  This will clean any corrosion that might be built up on the contacts.  Re-insert the RAM and see how your apps work.

I had this same problem and it was caused by the difference in metals between the contacts on my RAM and the slot.  Cleaning the contacts worked for me.

Good Luck!
zeppo14Author Commented:
Roadwarrior...thanks for your reply..I was hoping someone would say, " worries ...go for it!"
But alas there appears to be no simple answers when it comes to RAM.
Unfortunately, there seem to be so many variables.  I've been thinking, if I can just pick up a couple of sticks of 8Mb Fast page, for not too many $, and see how I go: if it doesn't work out hopefully I won't have lost too much.
May try to borrow some as suggested.

Loki, thanks for your input.
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Take a _VERY_ close look at the labels on each chip.
Check the last part of the string.
Look for '-60' or '-6' or '-70' or '-7' or '-80' or '-8'.
Do all four SIMMs have the same values?
If not, put the SIMM with the largest value (treat '-6' and '-60' as identical, and '-7' and '-70' as identical, and '-8'...) into the SIMM slot labelled #1.

Your computer will measure the speed of the first SIMM, and will access the other ("faster") SIMMs at the speed of the slowest, rather than what you may be doing now, i.e., trying to access a "slow" SIMM at the speed of the "fastest" SIMM.
Won't you work a little faster said the Fast Page to the EDO,
There's an SDRAM right behind us and he's stepping on my I/O....
Road Warrior basically has the correct answer, plus you may have some metal to metal problems (gold vs. lead--bad thing); my two cents is that I have several machines running mixed edo and fp (in pairs-of course) running the same speed but by several different manufacturers in each pair and I have never had any memory problems (and they run seti@home packets 24 hours a day). You just can't put one edo with one fp or two mis-speeded pairs together. (Although I have violated the latter with some sucess.)

Good Luck.
zeppo14Author Commented:
Thanks Otta, alhaqq for your input.  I have accepted a comment as answer.
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