using PC100 on 66MHz board


Aug 14, 2001
I have been trying to use PC100 RAM in a system with a 66MHz memory bus. I am under the impression that in general this should work, however I have had no success. The system will not boot at all while the PC100 RAM is plugged in. I have checked the specifications for the two systems (the PC100 ram came out of a similar but newer ocmputer) and they seem compatible. The CAS delays are the same and the number of clocks should be compatible. If anyone has any ideas why I would be having trouble, I would greatly appreciate some advice.



Dec 31, 2007
Make sure you mobo can handle whatever size stick you have. It sounds odd though it should work unless something is'nt set right. Have you tried the stick in all your dimm slots. I had a problem something like it with a k6-2 that you had to put the biggest stick in dimm 1.

When I go into a computer store I lose all means of reason for some reason.


Dec 31, 2007
clear CMOS and check the RAM.

some DIMMs might not work on some board, might need to reprogram the SPD.

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Mar 25, 2001
Unfortunately you don’t provide any info on your motherboard/chipset and the main thing: the memory itself.
That’s why I’m giving you the worst scenario as an example.
For old motherboards before buying double check the amount of cachable memory for your sise of cach memory on your board.
For example, for the Intel® 430TX, 430VX PCIsets it is very important (either PC-100 or PC-133 work though). Otherwise it's possible your cach memory won't work at all and you'll get a slowdown instead, after adding more than 64 MB of main memory. Your chipset second level (L2) cache controller might supports a writeback cache policy for cache sizes of 256 Kbytes and 512 Kbytes. Cacheless designs are also supported. For information on the chipset, see Intel's documentation:
<A HREF="" target="_new">Intel, Design, Chipsets</A>

Probably after looking through the specifications for your chipset, you’ll be lead to the conclusion that it will not run with chips over 8 megs each, hence you need a RAM module with at least 8 chips, to make a total of 64 megabytes.

Also, you gotta be careful around 64 megabit chips on the modules. They were new at the time, and they're are some special settings.
IT will problably work, but there is a possiblity that it might not, so be careful.
Try to disable SDRAM speculative read, anyway you’ll gain more improvement if compare with old-fashion 60 ns EDO.

Better make sure you can get a refund, just in case you can't get it to work.


I have tested HUNDREDS of older motherboards and can tell you this:
1.) PC100 works on ALL SDRAM Motherboards. So does PC133.
2.) Some motherboards limmit the size of memory used, but larger modules should still allow it to post. The usuall limmit for the Intel TX chipset is 128MB, though most motherboard manufacturers say 64MB.
3.) The Intel VX chipset will not read over 2MB PER CHIP. So if your module has 16 chips, it will see it as 32MB, regardless of how big the modules are (if they are 2MB each, your fine, but if they are 4MB your module will show up at half it's size, etc.)
4.) NOT ALL DIMMS ARE SDRAM! This is probably where your problems lies. MANY older systems, especially OEM systems from Dell and Compaq, used EDO DIMMS!
5.) Many, but NOT ALL, systems that came with EDO DIMMS could also use SDRAM, but not both at the same time! Try removing your old memory and put the new memory in DIMM1 socket. If that works, your old memory was probably EDO and not compatable with your SDRAM. If it does not work, your system is probably not SDRAM compatable at all!

I'm so tired of cookies I'd settle for spam!


Aug 14, 2001
Thank you to everyone who has replied to my question. Here is a bit more info that should probably clear up any confusion about what I was trying to ask:

My computer uses an Intel 440LX Chipset, and after checking things out I really think the new RAM should work. Here are the memory specs from the computer the new (PC100) RAM was taken from:

Architecture .. . . . . non-ECC SDRAM modules
DIMM sockets. . . . . . three; gold contacts
DIMM capacities . . . . 32, 64, and 128 MB
Minimum RAM . . . . . . 32 MB
Maximum RAM. . . . . . 384 MB
Frequency . . . . . . . 100 MHz
Clock cycle . . . . . . 10 ns (supports four clocks only)
CAS latency . . . . . . 3
SPD revision. . . . . . 1.2
Buffering . . . . . . . unbuffered
Voltage . . . . . . . . 3.3 V
Data bus width . . . . 64 bits
BIOS address. . . . . . F0000h

Here are the memory specs from the older computer (66MHz memory bus) that I am trying to put the memory in:

Architecture . . . . . ECC or non-ECC SDRAM modules
DIMM sockets . . . . . three; gold contacts
DIMM capacities. . . . 16, 32, 64, and 128 MB
Standard RAM . . . . . 32 MB (non-ECC)
Maximum RAM. . . . . . 384 MB
Frequency . . .. . . . 66 MHz
Clock cycle . . . . . 15 ns (supports 2- or 4-clock DIMMs)
CAS latency. . . . . . two clocks
SPD revision (minimum) 1.0
Buffering . . . . . . unbuffered
Voltage. . . . . . . . 3.3 V
Data bus width . . . . 8 bits
BIOS address. . . .. . F0000h

I have tried removing all of the original memory from the 66Mhz system and putting in one DIMM from the PC100 system and the computer will not boot at all. I hear that fans start up and that is it, the screen does not turn on and I don't even hear any BIOS beeps. Is is possible that I need to change some system settings before installing the new RAM? I was under the impression that the system would at least try to boot and then I could change the settings afterwards. The only thing in the above specs that bothers me is the 8bit data bus in the slower machine, but I am quite sure that this is a typo since it uses SDRAM DIMMS. I hope this info clears things up, and thanks again for your continued help.


are u just using the 1 pc100 stick? cause i has trouble on my old p2 comp, where i tried using both pc66 and pc100/133 together and it wouldnt work. so i had to take the pc66 out and it would work fine.

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