I just upgraded my first generation 15" aluminum 1ghz Powerbook to a total of 1.25gb RAM and along the way had an odd experience. Following the instructions in the manual, I opened the little door, removed the existing 256 MB SO-DIMM from the uppper slot, and restarted. But the computer only recognized the new 1GB DIMM and thought the original 256MB in the lower slot no longer existed! Looking through the manual there was no note saying which slot you need to install into. So I opened it up again, swapped slots, restarted, and now the full 1.25gb was recognized. Odd. Maybe I dislodged the bottom DIMM somehow, but I doubt it. Anyone else ever seen this?

Also, I know that everyone has their favorite places to order RAM and I was about to use one of them, but happened to be near my local CompUSA so I thought it was worth a look. Glad I checked, the 1GB DIMM was around $50 less than Crucial. But the bargain was a sale on 512MB PC2700 SO-DIMM's which are only $50 after rebate. The sale only lasts another day or so.

I'm not a huge CompUSA fan, but in their favor... if there's any kind of problem you can go back and I've had good results in the past when I needed to exchange something. As always, your mileage may vary, but maybe this can save someone a few bucks that wants to upgrade...

Well I spoke too soon. My Powerbook only recognized the RAM in the lower slot for a few minutes, then it disappeared and no amount of futzing would bring it back. Turns out this is a hardware problem that a number of people are experiencing. I have dedicated a new thread to the topic:

http://www.dvinfo.net/conf/showthread.php?t=44826

Boyd,

I have a somewhat fuzzy recall that you can't mix different dimm sizes in Apple computers i.e. if multiple slots are occupied the dimms must be identical pairwize. There should be something about this in the manual.

Thanks AJ. Some models do have this limitation I think (maybe the G3 or early G4 towers, can't remember). On the G5's you have to install in matched pairs. But it is not a problem to mix different sizes on the Powerbooks - or at least Apple has never said that it was, and many people use different sizes. It would seriously limit your expansion options if you could only upgrade in pairs... you'd end up throwing away lots of RAM :-)

Unfortunately, this is some sort of a hardware failure on the logic board that many powerbook owners are experiencing. The lower slot on my computer is dead... if I remove the expansion memory and only leave Apple's original DIMM in the lower slot (as shipped from the factory) the computer won't boot because it thinks there is no RAM installed. If you move the same chip to the upper slot it works fine.

So if you own a 15" powerbook (possibly other models too, including the G4 iBook) keep an eye on this to be sure all your memory is still available. Also a good reason to buy Applecare...