64 bit needs more memory than 32 bit

Discussion in 'Java' started by daniel.shaya, Jan 24, 2007.

  1. daniel.shaya

    daniel.shaya Guest

    It is clear from writing a simple program that creates Strings, that
    almost double the amount of memory is necessary when running on a 64
    bit jvm (I tried this on windows).

    Is there any way to reduce the amount of memory (a jvm setting or
    something) - or is this just the penalty for running on 64bit?

    Thanks in advance.

    daniel.shaya, Jan 24, 2007
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  2. daniel.shaya

    Tom Hawtin Guest

    There are two issues here.

    Firstly, if you have 64-bit addresses, then they are going to take up
    twice as much memory as 32-bit addresses. AIUI, on non-x86 the extra
    memory bandwidth can cause a slowdown of around 10-15% (AMD64 is more
    than compensated by not sticking too closely to the x86 design).

    Secondly, IIRC, client HotSpot does not run on AMD64 (or "EM64-T").
    Server HotSpot uses more memory.

    Tom Hawtin
    Tom Hawtin, Jan 24, 2007
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