[Ham-Linux] linux and ram

[Bill Anderson]

Memory management on the i386 architecture is a bit more complicated than
presented above. When you hear the term that a process is allowed 2G of
memory, it really means 2G of address space. Linux builds a memory map of
the process, but does not load the entire process into memory. On the i386
architecture, memory is divided into 8meg pages. The top command is one
tools that shows the difference between virtual space and actual physical
memory (RES) used. The processes with 0 for virtual and real memory are
kernel processes, and the kernel has its own 2G of virtual memory space.

The kernel only keeps in memory that which is being used. When compiled, the
optimizer tries to keep code together so as to minimize cache swapping, this
means that the code also operates in small units. The kernel treats data in
much the same way. The difference is that it can't trash pages that are
dirty (changes were made to the data in the page). These pages are retained
in memory as long as possible to minimize swapping.

I haven't even dealt with the zones created by the i386 hardware
architecture, and the issues with the MMU. Yes, PAE allows more physical
memory in the machine, but do you really need it? I have four machines
running seven distros of Linux. Only one machine has 1 Gig of memory,two
with 512 Meg, and one with 256 Meg. The 256 Meg works great for all the Ham
Radio applications, as I used the XFCE desktop. XFCE is not fancy eye candy,
but it does the job. Have I every wished I had more memory. The laptop I am
using now is running MySQL, Apache, and I often have seven or eight windows
open to do Web development. I reboot once a week to do backups, and that is
it.

If I were using vertualization, then memory becomes critical. I wouldn't
even think of running any form of virtualization without at least a gig of
memory.

Bill Anderson
WW7BA

On Wed, Feb 11, 2009 at 4:33 PM, Dr. Gerald N. Johnson <
geraldj at storm.weather.net> wrote:

> On Wed, 2009-02-11 at 17:55 -0500, Jonathan Thawley wrote:
> > what is the max amount of ram that linux will see on 32-bit vs 64-bit?
> >
> > are there many compatibility issues with programs running on 64-bit
> > linux as compared to running 64-bit windose, etc?
> >
> >
> > I know to recognize over 4GB RAM in windose you have to be running a
> > 64-bit version... is this the same in linux?
>
> Yes, its universal. 32 bits can only address 4 GB. 4,294,967,269 Bytes
> to be precise.
> >
> >
> > Thanks in advance...
> >
> > Jonathan
>
> 73, Jerry, K0CQ
>
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-- 
Bill Anderson
WW7BA
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