[CentOS] 64-bit CentOS 4.2 -- What is x86-64? "Long Mode" memory model ...

[Bryan J. Smith]

Fong Vang <sudoyang at gmail.com> wrote:
> What exactly is different between the 32 and 64-bit version
> of CentOS 4.2?  The kernel (drivers, file system, etc.) is
> probably compiled to support 64-bit and probably glibc.

It's all about memory models.  For more, see my blog:  
http://thebs413.blogspot.com/2005/10/what-is-x86-64-long-mode-memory-model.html
 

Almost _everything_ in a Linux/x86-64 distro is PAE52 --
52-bit Processor Address Extensions (PAE) aka "Long Mode." 
The kernel, GLibC, all /lib64, /usr/lib64, etc...

The PAE52 kernel can also still run PAE36 (36-bit PAE) and
32-bit applications.  Hence why a few 32-bit libraries are
still included under /lib, /usr/lib, etc...

But PAE52 programs cannot use PAE36 or 32-bit libraries and
vice-versa.  That's where the issues arise.  That's also why
we include a few 32-bit libraries, for the few 32-bit
programs you might want to run.

> What're some important differences between the 32 and
64-bit
> version?  I'm just trying to get a deeper understanding.

It's all about memory models.


-- 
Bryan J. Smith     Professional, Technical Annoyance                      b.j.smith at ieee.org      http://thebs413.blogspot.com
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*** Speed doesn't kill, difference in speed does ***