[Tfug] 32bit os on 64 bit system

[John Gruenenfelder]

On Sat, Sep 26, 2009 at 10:03:35AM -0700, christopher floess wrote:
>On Sat, Sep 26, 2009 at 9:34 AM, Jim March <1.jim.march at gmail.com> wrote:
>> Well I have found one advantage, and it's a *weird* one given the history:
>
>Jim, I remember reading some of you stuff about flash on 64bit and it
>sounds enticing; I'm in the middle of an internship in Berlin, and
>when I'm craving some familiar American entertainment, it almost
>always involves flash.
>
>Since I only have 1.5 gB of ram, I think I'll hold off for now though,
>especially considering that other input seems to suggest that I'm not
>a complete fool for running 32-bit  on a 64-bit system. I don't know
>how I missed the fact that I bought 64-bit architecture. Normally I'm
>a careful shopper.

I've never had a 64bit system with less than 2GB of RAM, but I can tell you
that 64bit distros work just fine with 2GB.

Whether or not you switch to 64bit can also depend on your intended use for
the machine.  If you plan to do some heavy computing and data processing, you
will likely benefit from the increased data transfer to/from RAM.  64bit
instructions move twice the data as their 32bit counterparts.

I asked one of my comp. sci. professors about this once and he gave
essentially the above argument and also added that on a 64bit CPU you can
expect the 64bit instructions to run slightly faster than the 32bit
instructions.  But, he may have been talking about the overhead of executing
32bit ops in a 64bit mode.

>As far as Zack's input goes, which posted after I started this reply,
>I think that when the time comes for an upgrade, I will simply
>re-install with 64 bit instead of recompiling the kernel.

Yes, if you do upgrade, go this route.  I don't think you will find much
change at all by just changing the kernel.

When I compiled my first kernel for a 64bit system, I couldn't understand why
the kernel config looked almost exactly the same.  That was because I didn't
have a 64bit system underneath (i.e. no 64bit compiler/libs).  So, while the
new kernel could execute 64bit code, it was otherwise identical.

Do the same thing from within a 64bit environment/distro and you will find
that the "architecture" sections of the kernel config are vastly different
*and* much smaller.  It's amazing how much x86 cruft has built up since the
first 80386.  Virtually all of that disappears with x86_64.  It's a clean
slate with a new ABI and a new base set of assumptions for what the CPU must
support by default.


-- 
--John Gruenenfelder    Systems Manager, MKS Imaging Technology, LLC.
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