On Jan 12, 2009, at 9:23 AM, Michael Ash wrote:
That's it! Pointer size and native 64-bit integers are the only difference between the two!
In addition to what Mike said, the transition from X86 to X86-64 includes a few other benefits besides larger pointers and native integers. The number of registers were doubled, and the calling conventions were changed so that 80% of the time function/method arguments are stored in CPU registers instead of being placed in a four-byte-aligned position on the stack. And that 20% of cases only happen when you pass in a structure larger than 128 bits, or pass in an unaligned structure, or have a function that takes more than 6 arguments.
So typically a program ported from X86 to X86-64 will run just slightly faster, especially if the program passes around a lot of 64- bit arguments. This doesn't apply to the PPC64 architecture, which is almost unchanged from PPC, and so PPC64 programs are typically slower due to the extra overhead.
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