The chip is for an iMac (desktop) not iBook (laptop) and I think there may be significant size/shape differences even for the same specs. I've been trying to do some research on the topic and keep getting bogged down by the cheap memory vendors coming up top in all the keyword searches. (It's also becoming clear that the street market for memory is lower than the "genuine Apple part list price" suggests, so maybe I'm not being quite as profligate as I thought.)