I'm considering upgrading my 1.67 GHz Powerbook G4 from 1.5 GB to its maximum of 2 GB (hoping this will boost its performance a little), but I'm uncertain about which memory module to buy. I just popped up my Powerbook to see what's inside: one slot contains a 512 MB module (a Samsung M470T6554CZ3-CD5 which came with the machine) while the other slot contains a Kingston 1 GB module marked KTA-PB533/1G which I added myself. I assume I need to get another 1 GB module to replace the 512 MB module for a total of 2 GB. I've read that you need to match memory modules, but I'm uncertain if this means getting the exact same brand/model, or if it just means that I need to pair the amount of memory (which I haven't done with my current setup, thought it seems to have worked fine all along), or I literally need to get identical modules? I looked up Kingston's memory search tool to see what to get for my machine which resulted in a KVR533D2S4/1G, but it's almost twice as expensive as the KTA-PB533/1G. It seems that the former is "system specific" for my Powerbook while the latter is "generic". Does it make any difference? Can I get another Kingston KTA-PB533/1G (which means I definitely have a matching pair), should I get the more expensive KVR533D2S4/1G for better performance (but no matching pair), or am I screwed either way because I should have bought the KVR533D2S4/1G in the first place, so what I really need to do now is buy two KVR533D2S4/1G modules making it a "system specific matching pair" and throw away my (seemingly) perfectly working 1 GB (and 512 MB) modules? I'm also considering upgrading a recent (2008) 2.4 GHz iMac's memory from 1 GB to 4 GB, and wondering about the same thing there.