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On a 64 bit Windows7 machine will I get better VirtualBox guest performance running 32-bit or 64-bit Debian?

I want to run the guest as a LAMP server.

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migrated from stackoverflow.com Jul 3 '11 at 22:16

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A 64-bit system doesn't have any intrinsic performance improvement over a 32-bit one, apart from being able to use more memory. If the guest machine doesn't have at least 4 GB of memory, x64 will give you no benefit at all.

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But note that compilers will have plenty more register space to optimize in. Of course, data will frequently take up twice the space, but some data are fixed size (say, bytes). These will be handled more efficiently; The savings in more opportunity for register-based parameter passing instead of stack-based are not something to spit at. I've done recent benchmarks with heavy computation-intensive tree search algorithms that were a factor of 1.1 to 1.2 faster in 64 bit due to this effect mostly. Not shocking, but worthwhile –  sehe Jul 3 '11 at 22:58
    
So user22394, you're saying it will make no difference to the OP running a LAMP server? –  saschabeaumont Jul 4 '11 at 2:14
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I wouldn't agree with that, @sascha. The AMD64 (EM64T, x86-64) extensions double the number of general purpose registers from 8 to 16, and any program complied for AMD64 will take advantage of this additional workspace because it must be present. It depends on what the system is doing if these registers will help or not. –  Bacon Bits Jul 4 '11 at 5:16
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I agree that for heavy number crunching 64-bit can actually help; but I don't think a LAMP server could benefit at all from it. –  Massimo Jul 4 '11 at 5:18

If performance is the only factor you care about, it really would be better to use 32-bit instead of 64-bit because you could disable the IO APIC feature then, which runs quite faster. This is VirtualBox-specific, BTW.

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Each cpu might be faster, but according to Why should I enable IO APIC in VirtualBox? - Server Fault, without IO APIC, the guest will not be able to use more than one virtual CPU in the virtual machine, which sounds like a big thruput reduction for most LAMP servers. –  nealmcb Mar 30 at 15:30

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