Re: perspectives on 32 bit vs 64 bit
Hi,
Thanks for your comments.
On Fri, 30 Sep 2005, Lennart Sorensen wrote:
On Fri, Sep 30, 2005 at 03:19:33PM -0400, Faheem Mitha wrote:
What is the 4 Gig limit for 32 bit processors that people talk about? Does
this mean that each process/thread can only get a limit of 4 Gig? Is there
any workaround for this?
Well given a 32bit program only has 32bit pointers, there isn't any
clean simple way to gain more memory. I believe right now applications
can have up to 2GB, although some kernel patches/settings allow up to 3
or 3.5GB/application by shrinking the kernel's piece.
I'm using the stock Debian AMD64 SMP kernel. Do you know what the memory
value per application is for that?
I don't understand why so much of the memory is taken by the kernel. If
each application is 4GB, then why is the kernel taking as much as 2GB?
Does that mean that the application only gets 1/2 the memory that the
operating system has allocated to it? What is the other half being used
for?
If you have no applications that need more than 2GB memory for
themselves, and you aren't using lots of floating point (although
you can compile for sse on 32bit too for that matter), then there is
nothing wrong with sticking with 32bit for now until you think
everything you want is available for 64bit.
And if yu have 1 or 2 programs that could use 64bit, use 64bit
versions of those as long as you run the 64bit kernel on your 32bit
system. Works for me.
Well, the machines are being used for a bioinformatics research group, so
they might require a lot of memory. 2GB is not really very much.
Also, isn't there a problem when compiling external kernel modules
with a 64 bit kernel on a 32 bit system? I had problems with the
Nvidia kernel for the graphics driver, for example.
Also, I've had problems with 32 bit programs on 64 Debian, since they
require 32 bit versions of libraries, which are not available, since the
Debian port is pure64.
One option is to run a 64 system with a 32 bit chroot. I think there
should be no problem with this. However, I was wondering if people has any
idea whether it was possible to use the regular /home from inside the
chroot. Also, is it possible to have X forwarding working from inside the
chroot (assuming one is logging into the regular system)?
One more question is whether there is any problem sharing a home directory
between a 32 and 64 bit Debian system on an amd64 (assuming one is
dual-booting)? I'm just talking about ascii here, I know that binaries
would need to be recompiled.
Thanks for your help.
Faheem.
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