tuartboy said:
yeah, it was my understanding that the 12" PB was fixed at 1.25gb only because the largest notebook ram available is 1gb. I doubt it has a different memory controller than the 15" which can hit 2gb because it doesn't have a fixed 256.
Right, but wrong.
If they have the same memory controller, the 12" will be forever limited to 1.25 Gb, because it has one socket and the 15" has 2 sockets. The limiting factor in the memory controller is the number of rows and columns it can address on the chip -- not the total amount of memory. (there are secondary limiting factors as well such as the number of chips and the organization of the RAM into banks)
A 2 Gb module (which would be required for the 1 socket 12") would have to have chips that were twice as dense as the 1 Gb module (or would have to stack 32 chips on a module). In either case, the memory controller simply would not have the ability to call the memory locations of half of the addresses available.
Hypothetically then, if the 12"
could go to 2.125 Gb, then the 15" could go to 4 Gb
In rare occasions, like the iMac G4 DDR machines, the memory controller has the ability to address a larger memory space than was originally specced - which is why the iMac G4's with DDR RAM can use 1 Gb modules even though the original spec is for 512 Mb modules maximum.