I have 256mb 133 cl2 in my dell optiplex gx150, 1ghz processor. when i put my new 512mb STICK in (512mb pc133 cl3 3.3v) the computer doesn't boot at all and just beeps once per second. is cl2 interchangable with cl3? if not i can exchange the ram. thanksNot all RAM is interchangeable. Go to www.crucial.com and input you system info and you will see what you need. In your case:

http://www.crucial.com/store/listparts.aspx?model=OptiPlex+GX150+Series

I am assuming you installed it PROPERLY. The general rule of thumb is to put the largest module in Slot 0 (nearest the CPU). While doing this, remove the old RAM and see if the 512 is recognized CORRECTLY in the BIOS (F2 at boot when you see the Dell logo. If it is add the old chip next to it and repeat the procedure.

It may just be incompatibility, but why BUY the wrong thing? Let us know.Thanks for that site, according to it my computer can only take 512mb of ram (total bummer). Is there a way to change that?

Anyways, both cl2/cl3 are compatible. The only thing is there was no 512 sticks at all on that page you gave me. Why buy the wrong thing? Because I didn't know any better. Now I do. So I guess I'll have to trade my 512 for another 256. It's odd that I have to have 2 sticks and can't use one 512, but whatever. Thanks.Glad you are all fixed up and thanks for posting back. It is fortunate that you will be able to trade for the right thing, and now you know more about RAM.