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Re: Debian Lenny 32

Camaleón wrote:
> Stan Hoeppner wrote:
> > Camaleón wrote:
> >> Mohamed Daif wrote:
> >>>   What is the maximum RAM supported in Debian Lenny 32bit .
> >> 
> >> It should be 64 GiB with a PAE enabled kernel (bigmem).
> > 
> > 64GB max for the kernel, but userspace processes are still limited to a
> > 4GB virtual address space.  Thus if one has an application, say a
> > database or medical imaging app (think MRI), that requires direct access
> > to say, 32GB of RAM, one should be using an x86-64 kernel and an
> > application compiled for an x86-64 target.
> That's a self-imposed limitation. 

What is self-imposed?  4GB of virtual address space?  That is the
definition of a 32-bit address space.  It is only self imposed if you
include choosing a 32-bit architecture in the choice.  And actually
unless you do special things you really will be limited to 3G.  (It
used to be that you couldn't get above 2G without linking with -N.
But things have been rewritten to make 3G the default now.)  Going to
64-bits is the much easier way to make use of a large memory space.

> It could be by-passed by using "memory mapping" techniques (this is 
> documented in the wikipedia page you pointed out about PAE, which 
> specifically mentions "mmap()") but not many linux applications are 
> making use of it, I'm afraid, contrary what happens on Windows systems. 

None of that is real memory.  Even if an application codes in the
ability to use application level paging to handle more data the
program itself is still limited to 32-bits.

(There are a lot of wonderful Seymour Cray quotes, or at least
attributions to him even if he didn't actually say them, that I really
wanted to say here about memory.  Consider this an "in" joke for
everyone who knows what I am talking about.  I will leave with this
one: "Virtual memory leads to virtual performance.")

> In the end, applications that need to handle/move big quantities of data 
> directly from the RAM will benefit of a pure 64-bits OS.

Agreed.  But I don't think we have gotten to the point where most
desktop users need it yet.  *Wanting* it is fine though.  But even
most people's pig applications of libreoffice and firefox don't
usually need more than 3G of memory.  But of course if there is any
application (usually scientific or some other technical domain) that
needs more than 3G of data space then they really do need a 64-bit
architecture.  They usually already know who they are.


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