What's up with new PC133 memory?

It’s been a while since I’ve purchased PC133 memory, since my newer machines all use DDR; however, I just ordered a 256MB DIMM from Circuit City to upgrade an older but still usable PC running a PIII/500 (with a 100 Mhz bus). When I got the memory, it stated on the package that it was only usable on machines running at 733Mhz and faster. What’s changed? In the past I’ve always bought PC133 over PC100 because they were usually the same price, they were all compatible, and I figured I could still use the PC133 if I decided to upgrade the CPU.

Could you post the brand & model number?

It’s Centon 256PC133ONLY 163640, but I’ve since seen similar restrictions with other brands.

I assume the “ONLY” refers to the fact that it only works with 133Mhz buses, but that wasn’t too obvious when I ordered it.

The newer memory is using larger size individual chips, which many older mainboards cannot address the full size. They’ll either detect them at half the size, or not at all. The only way to know is by giving it a try, you won’t be hurting anything. Make sure you can return them if they don’t work. Some mainboards might accept the newer memory with a bios upgrade as well, YMMV.

Why would they rate it by bus speed, then? On the back of the package, it specifically says “733 Mhz and above processors that use the following chipsets”; it then goes and lists a bunch of chipsets from AMD, Intel, SiS and Via. I’ll have to check to see if my chipset is among the listed, I guess, but I’m still wondering about that bus speed.

I think the bus speed is simply a simplified way for them to refer to an era of technology. The bus speed is used as marketing speak, not techno speak.

You can still use the ram. It just may not run optimally.

I don’t think it’s a chip size issue. Looking at Pricewatch I see listings for PC100 DIMMs up to 1 GB. If we assume that there’s a maximum of 16 chips per DIMM (a safe assumption) or 18 if it does parity checking, that would imply that you could only go up to 256MB with the “safe” technology (the DIMM that I bought is single sided).

LSLGuy, that’s kind of what I suspected, but why then does the company also offer 256 MB PC133 DIMMs that are supported on PC100 machines.

Daizy, what exactly do you mean? What would cause it to run less than optimally?

Hi Running with Scissors
Poor choice of words is all. The sticks are meant to run at 133…but they will run at 100.

Probable causes could be if the stick is running alongside another stick of for example: PC100 ram - the bios settings will not be able to accommodate both sticks with the same setting. And there’s the matter of ram speed vs. bus speed - 100 MHz <-> 133 MHz. The stick is optimized for use in a 133 FSB system and will be running at 75% of that speed - so it will be out of synch with the general bus speed.