MBP SR and 64bit processor???

[Jestered]

My questions is this:

I have always thought that the MBPs have been 64bit since they went to C2D (Merom), but I keep coming across people that are posting that the new MBP Santa Rosa is the first "True" 64bit processor.

Can anyone explain why the SR is a "True" 64bit processor and the others aren't?

Thanks

 

[jdechko]

The C2D is a true 64-bit processor, but the platform it's been built on doesn't support all the features of a 64-bit platform. The processor used is essentially the same old C2D design on a new platform (Front-side bus, northbridge controller, etc).

On the old (Napa?) platform, the chipset limited the amount of RAM that the computer could recognize and use to 3GB, while a 64-bit computing system didn't have this limitation and can address many more GBs of RAM (not sure of the max, but it's a lot). With the SR platform upgrade, the MBP can address 4GB and above of RAM (something a 32-bit system can't really do - My computer, while it has 4GB of RAM installed, can only see 3.25). In the future, when there are cost-effective 4GB modules, we could see 8GB (and above) of RAM in the SR MBPs.

 

[PhatBoyG]

Santa Rosa has a 36-bit memory bus, up from the 32-bit memory bus of previous platforms.

This allows the system to fully utilize 4GB of RAM, unlike previous systems that could only see something like 3.3 GB with two 2GB sticks. All those PCI-x devices have to map into RAM somewhere, and pre-Santa Rosa, that was overlapped with RAM so the RAM lost out.