What's the difference? I have two computers, systems are 300mhz, Win98SE... and 700mhz, Win2000PRO. Both have 256mb RAM with two sticks 128mb PC100 each. I have a stick of 256mb PC133 that I got from a discarded computer. I first tried it in Win98 comp. and it worked with no problem but only gave 128mb giving me 384 total. Then I tried it alone in the Win98 and still only got 128mb. I did the same procedure on the Win2000 comp. with the same results. I don't understand why, but even by itself, it only gives 128mb on both computers. But anyway, should I go ahead and use it, or could it cause problems down the road being that it is a different type?