Any reason NOT to run 32 bit apps on 64 bit Windows?

Discussion in 'Windows 64bit' started by Jim, Sep 23, 2006.

  1. Jim

    Jim Guest

    Scenario:

    I'm implementing servers that will run a new application that consists of
    the app itself and a database. They're all X64 CPU boxes and there are 64
    bit drivers for all my hardware. My company's developers are writing the
    app from scratch. I'll be running 64 bit Windows Server 2003 R2 and 64 Bit
    SQL Server. The app won't require more than 2 GB of memory and won't
    otherwise benefit from X64, but that's what's available from my hardware
    manufacturer these days, so it's an X64 box. So, the questions:

    1) Should I run 32 bit or 64 bit Windows on my app servers? Why?
    2) Should the app be written so that it can run on 64 bit Windows or just 32
    bit?

    I ask the questions because I'd like to standardize as much as possible.
    All machines are X64 machines, I'd like to standardize on X64 Windows, but
    the article at http://insight.zdnet.co.uk/0,39020415,39281436,00.htm says

    "In fact, there can be a slight performance decrease caused by the switch to
    a 64-bit processor, because the larger memory address pointers take up twice
    as much room in the cache."

    There are no benchmarks to backup that statement and what "slight" equates
    to is questionable. Does anyone know of any downsides to running 32 bit
    apps on Windows 64 bit (performance or otherwise)? Is performance really
    degraded, and if so, by how much (i.e. do you know of any real benchmarks
    done or is this just a theoretical statement)?

    Thanks,
     
    Jim, Sep 23, 2006
    #1
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  2. Jim

    John Barnes Guest

    IMHO
    If you are going to need any 64-bit applications such as 64-bit SQL you will
    have to run a 64-bit os
    If the application will NEVER need to be run on a 32-bit os, write it so it
    will run native 64-bit
    The size of the cache for direct addressing doesn't slow anything. The fact
    that it has to call the emulation layer does, but everything posted here
    suggests that the difference is infinitesimal.

    see above.
     
    John Barnes, Sep 23, 2006
    #2
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  3. The more CPU intensive your application is, the higher the chances are that
    you'll see a speed increase when targeting x64. I've seen speed increases
    of 23% simply from recompiling for x64 native. Primarily due to the larger
    register set available in long mode.
     
    James Robertson, Sep 25, 2006
    #3
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