I want to upgrade my Compaq 5010US from 128mb to 256mb RAM. Not sure which chip is right: Some "configurators" show a PC100 and some a PC133. Does anyone know if it matters which one I use?

Hello E.J. I just recently upgraded the memory in my computer from 128MB to 384MB. I had the same question as you--should I use a PC-100 or a PC-133 module? It appears that all memory used to be backwards compatible, but today some are not. In other words, if your computer has a 100 MHz FSB, you could use a PC-133 module, but it would run at 100 MHz, not 133 MHz. PNY Technologies asserts that their modules are no longer backwards compatible. However, when I was researching which module to use, I discovered that Kingston and Crucial disagree, as both companies listed a PC-100 and a PC-133 module for my computer and guaranteed compatibility. It should be noted, that several local techs advised me to "match" the 100 MHz FSB in my computer, so I opted to go with a PC-100. Anyway, I hope this info helps you in making a decision. Best of luck...texascowboy3000.

Also be aware that compaq's hardares are different than others' becase they're not compactible. I have a feeling that other memories will not work but compaq's. And I can't guarantee. But I had experience of failing to upgrade a computer with a compaq manufactured memory chip; and not upgrade a compaq computer. Simpliy, I recommend you to ask the seller which is the right one for your compaq, or just by the compaq memory chip.

I also have a compaq.I added a 256 stick to my existing 64 megs.I was told pc133 was fine.it clocks back they said.And everything is working fine

Like Jim' I added a 256 stick to my existing 64 megs. Tried the 256 alone and it wouldn't work, put Compaqs 64 stick in slot 2 and everything worked great.