On May 4, 2006, at 12:28 PM, Kep Woof wrote:
it seems like a huge waste to run the i386 version on an
amd64 machine, but can anyone comment on the performance difference?

Sure. For the most part, if you don't have more than 4GB of RAM, there is little point to running in 64-bit mode. A more fine-grained analysis:

You can still take advantage of PAE and more than 4GB process address space on, say, a machine with 2GB of RAM, by using a lot of swap space or running a large 64-bit aware database. However, if you don't have more than 4GB of RAM [1], it's entirely possible that applications will run faster in 32-bit mode than in 64-bit mode, but it depends on the specific things you are running. IPv4 and character-related stuff (ie, byte fiddling/string copying) tend to be faster in 32-bit mode; things like SSL cryptography and big databases can prefer 64-bit mode even on machines without more than 4GB of RAM.


[1]: The real number is actually somewhat less than 4GB, more like 3GB or 3.5GB, since the kernel itself and hardware devices consume some of the top of the physical memory address map.

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