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From "Dale, Matt" <>
Subject RE: [OT] How much RAM can java use
Date Thu, 06 Oct 2005 16:18:34 GMT

On the 32 bit system you definitely won't get more the 2G without some kernel hacking and
you may well see even less than that.

On the 64 with a 64 bit JVM you should be able to use however much you like obviously leaving
some space for the OS to run in.

-----Original Message-----
From: Leon Rosenberg []
Sent: 06 October 2005 17:16
To: Tomcat Users List
Subject: Re: [OT] How much RAM can java use

On 10/6/05, Caldarale, Charles R <> wrote:
> > From: Leon Rosenberg []
> > Subject: [OT] How much RAM can java use
> >
> > Does anyone know for sure how much RAM I can use with JAVA 1.4 or 1.5?
> The answer is very platform specific.  For example, on a normal 32-bit
> Windows system, each process has a maximum of 2 GB to play with, but
> some of that is taken up by various .dlls.  (And unfortunately, these
> are scattered throughout the range, and the Sun JVM insists on having
> contiguous space for the heap.)  There is a boot option for some
> versions of Windows Server that changes the process virtual space to 3
> GB, at the expense of some kernel capacity.
> I've seen 64-bit Sparc systems with Java heaps sized at hundreds of
> megabytes...

Ok, I'll try to be more specific:

Debian 3.1, kernel 2.6.x-smp (32 bit)
Debian 3.1, kernel 2.6.x-smp-emt64 (64 bit)

Hardware: AMD Opteron and Xeon64 (both 64 bit)

SUN jdk1.5 and/or jdk1.4.2

4 GB total RAM for 32-bit linux, with 3/1 memory partitioning
16GB total RAM for 64-bit linux.


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