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From André Warnier ...@ice-sa.com>
Subject Re: [OT] Re: Maximum memory that can be assigned to Tomcat on windows platform
Date Wed, 30 Nov 2011 21:38:11 GMT
Francis GALIEGUE wrote:
> On Wed, Nov 30, 2011 at 18:51, Christopher Schultz
> <chris@christopherschultz.net> wrote:
> [...]
>> Running a machine with more than 4GiB in 32-bit mode isn't stupid at
>> all IMO. If you have relatively small processes, there's no need for
>> the overhead of 64-bit even if you have 16GiB or more.
>>
> 
> This is quite the opposite: a 32bit OS has _more_ overhead than a
> 64bit OS when running on a 64bit CPU.
> 
> Just consider filesystem calls such as read(), write(), seek(): their
> arguments are 64bits, not 32, and have been so before 64bit was even
> common (2+ GB files are common place today). With a 32bit OS on a
> 64bit CPU, you eat up two registers whereas a 64bit OS will take only
> one.
> 
> And of course, this is without considering wasted TLB space or the
> sheer time to address just one memory page.
> 

I am not knowledgeable at all in such questions, and while you are at it let me ask a 
question :
Does the fact of having a system with a 64-bit CPU (and OS) necessarily (or usually) imply

that data transfers between CPU and RAM happen also 64-bit in parallel ?

For example, let' suppose that I have an application which handles a very large table of 
integers (the integers themselves being < 2exp31), and that periodically all elements of

this table have to be updated.
My understanding is that under a 32-bit platform, each integer will occupy 32 bit, while 
on a 64-bit platform each will occupy 64 bit (the source program remaining the same).
If there is not a corresponding 64-bit parallel transfer between CPU and memory, then 
using a 64-bit CPU would be detrimental, no ?
Or is this a non-sensical case nowadays ?



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