Linked by Tony Bourke on Thu 22nd Jan 2004 21:29 UTC
Benchmarks When running tests, installing operating systems, and compiling software for my Ultra 5, I came to the stunning realization that hey, this system is 64-bit, and all of the operating systems I installed on this Ultra 5 (can) run in 64-bit mode.
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by MJ on Fri 23rd Jan 2004 23:47 UTC

Yes what you just described is true to a certain extent. However, in practice every data type on a 64-bit binary is not 64-bit only. 64-bit binaries might have 8,16,32 bit data objects in them and caches do allow you to address a byte in a cache line. All I am getting at is that it is not very accurate to say that 64-bit addressing automatically yields poorer performance due to higher cache-misses than a 32-bit binary. It is possible in the scenario you describe above.

In reality not every one who codes a 64-bit program makes all the data 64-bit quantities.

I don't dispute those statements at all. I didn't think that I said that this was automatically the main reason that performance degrades, but that it is one possible aspect to consider when keeping track of issues affecting the performance of 64-bit applications. Certainly this is only going to apply to a subset of objects in an application. I didn't mean to give the impression that this was the primary cause of a performance difference between 32 and 64 bit apps. It sounds like we're in agreement, though...?