What's the difference and can you use two ram chips together?
I recently upgraded my 15" Powerbook G$ ram from 256 to 512 and I noticed the two slots.
No difference. Just more upgradability. I currently have a 1GB and a 512MB in my MacBook Pro and had the same with my 1.67GHz PowerBook G4 before i sold it to get this.
Which card should go into the lower or upper slots? Does it matter?
So am I going to get 256+ 512 MB of RAM then? 768 MB?
I also read that G4 aluminum powerbooks had problems with the lower ram slots. Should I risk installing my old RAM card into one of the slots?
The upper and lower ram slots work the same.
Be bold, dare! Jam the Ram in! GO GO GO!
More ram is better! OS X loves RAM!
All kidding aside, there is so much info on the web, and on apple's website, you should go there and check it out.
Heres some: http://docs.info.apple.com/article.html?artnum=95132
Apple has a repair extension program for the powerbook g4 15" ram slots IIRC.
Fix It Guides for Mac Laptops & Mini
The guides can be viewed on-line or you can download a PDF file.
Mac Troubleshooting, Maintenance & Tips
The PowerBook G4 15" memory slot repair extension (at present) only includes the 1.5/1.67 ghz revision of the PB G4 15". As far as the issue is concerned, I haven't found that any user action causes it. So using both slots should not create any issues.