Pamela, as far as I know, the difference is in speed; PC100 is 100 MHz, and the PC133 of course 133 MHz. You might wanna check if that will make a difference in your computer, but generally the PC133 should be quite a bit faster, I assume. Michael Welbers --------------- From: "Pamela Plowman" <pamela at theplowmans.com> Subject: [P1] what's the difference between... Date: Wed, 17 Dec 2003 14:51:29 -0800 Message-ID: <017001c3c4f0$4fb9fd10$0202a8c0 at cbr929> What's the difference between PC100 SDRAM and PC133 SDRAM? I thought I heard somewhere that PC133 is faster so that is what I am thinking I want to get but I don't know if it will work with my Key Lime iBook (it's 466MHz and I am upgrading it to 576 MB RAM, but I need to know which module to get). Any help would be appreciated! Thanks, Pamela