sg, the data paths on 32-bit processors are all at least 64 bits. DDR is 64 bits wide, and Intel has used a 256-bit wide path to its L2 since the early P4s.
In addition, the FPUs have long processed 64-bit or even 80-bit chunks of data.
The 32-bit limitation on x86 procesors is that all of the integer registers used to address memory are only 32 bits wide. There are some kludgey segmented ways to extend this to 36 bits of address space but they are time consuming and have to be planned carefully.
Because of the 32-bit limitation on memory addresses, the Athlon and P4 also do not have much 64-bit integer calculation ability. One thing that AMD64 adds is full 64-bit-wide mode for all types of integer instructions, ANDs, ORs, XORs, add, subtract, multiply and divide. I think you can even do a 64 by 64 multiply and get a 128-bit result. These wide integer/logical instructions are 1) absolutely necessary if your program + data is allowed to exist in an address space > 32 bits, and 2) come in handy doing things like encryption, decryption and possibly encoding/decoding.
Because of (2), for example, I've seen benchmark results where DivX encoding doubled in speed using AMD64 code instead of regular x86 code.
Now, I suspect that the 64-bit extensions for Prescott have nothing to do with memory addressing, but they are probably just adding some of these 64-bit integer instructions. Kind of like a new version of SSE. So Intel will get great performance in a few optimized benchmarks that use this "SSE64" mode, but will have the same old address bits coming out of the CPU.
I'm not sure what the LGA 775 pin package is for. The reason I don't think Intel will try to extend memory addressing is because of what Sun'w David Yen said about a later version of Prescott: http://news.com.com/2008-7784-5089022.html --------------------------------------------------------------- SO INTEL PUT 64-BIT EXTENSIONS INTO PRESCOTT? Yeah.
WITH 64-BIT MEMORY ADDRESSING? With their 64-bit architecture, they will allow programs to have 64-bit addressability. --------------------------------------------------------------- Now I could be wrong, but to me, "with their 64-bit architecture" is probably referring to the Itanium, not the Prescott. Read the whole interview yourself and see if you agree.
The Inq also had a weird story a while back which claimed that the LGA 775 pin socket for Prescott was designed to allow a 64-bit "expansion module" to be plugged in above the CPU.
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