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From "Ilya Kazakevich" <Ilya.Kazakev...@JetBrains.com>
Subject RE: [OT] Re: Maximum memory that can be assigned to Tomcat on windows platform
Date Wed, 30 Nov 2011 21:52:45 GMT
>>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 ?
That depends on front bus width. Modern PCs has 64-bit bus AFAIK.

In "64-bit CPU" 64 is register size and nothing else (although 86x64 mode
has some differences with IA32)

>>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).
Java integers are always 32bit, are not they?

C int may vary from 16 (in BCC 3.1 for DOS) to 64. 

64-bit processor mode gives you ability to:
1) address more memory (2^64 bytes theoretically).
2) store more data in register so CPU could now operate 64bit numbers and
you need one operation to do something with two 64bit objects opposite to
two operations on 32bit.
3) v86 mode is disabled so you can't run 16bit apps :)
4) use new registers, new SSE instructions and so on:
http://en.wikipedia.org/wiki/X86-64#Architectural_features



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