32-bit Vs 64-bit questions

Eitan Hirsch

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Jun 13, 2006, 11:08:54 PM6/13/06

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we're currently running matlab 7.1 (32-bit) on a 32-bit processor,
and we're thinking of upgrading our system.
can anyone help with the following questions:

1. what are the advantages (if any) of operating the 32-bit Matlab on
a 64-bit processor (like the opteron)?

2. what are the advantages (if any) of operating the 64-bit Matlab on
a 64-bit processor?

3. what are the advantages (if any) of operating the 64-bit Matlab on
a Dual-core 64-bit processor?

4. what are the advantages (if any) of operating the 64-bit Matlab on
2 Dual-core 64-bit processor?

i'm pretty lost here, so any help would be appreciated.
thanks,
eitan

stu

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Jun 14, 2006, 1:26:56 AM6/14/06

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> we're currently running matlab 7.1 (32-bit) on a
> 32-bit processor,
> and we're thinking of upgrading our system.
> can anyone help with the following questions:
>
> 1. what are the advantages (if any) of operating the
> 32-bit Matlab on
> a 64-bit processor (like the opteron)?

nothing. just the advantage of the 64-bit system.

>
> 2. what are the advantages (if any) of operating the
> 64-bit Matlab on
> a 64-bit processor?

hopefully you will not be interrupted by the family of "out of memory" errors in matlab

Steve Amphlett

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Jun 14, 2006, 5:07:29 AM6/14/06

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Eitan Hirsch wrote:
>
>
> we're currently running matlab 7.1 (32-bit) on a 32-bit processor,
> and we're thinking of upgrading our system.
> can anyone help with the following questions:
>
> 1. what are the advantages (if any) of operating the 32-bit Matlab
> on
> a 64-bit processor (like the opteron)?
>
> 2. what are the advantages (if any) of operating the 64-bit Matlab
> on
> a 64-bit processor?

Leaving aside the obvious memory and/or large file handling issues,
you may be surprised at benchmark results. I know of some codes that
run slower when compiled 64-bit. I also know some that run faster
(I'm not talking ML here, just our own simulation codes written using
a mix of Fortran/C/C++). If I were you I'd install both versions and
benchmark your ML scripts.

Predictor

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Jun 14, 2006, 6:12:57 AM6/14/06

to

I suggest checking benchmarking already performed by others. Try, for
instance, searching for terms such as:

MATLAB 32 64 benchmark

...on places like:

AllTheWeb (http://www.alltheweb.com)

-Will Dwinnell
http://will.dwinnell.com

Titus Edelhofer

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Jun 16, 2006, 5:54:54 AM6/16/06

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Hi,

1. should behave more or less the same as on a PC (only that the
opteron even as 32bit is fast!)

2. 64-bit MATLAB handles matrices up to 16 GB of memory!

3. nothing

4. not much, only that the 2nd processor can be used for other work
while MATLAB is using 100% of the first

Titus

"Eitan Hirsch" <eita...@alum.cs.huji.ac.il> schrieb im Newsbeitrag
news:ef395...@webcrossing.raydaftYaTP...

the cyclist

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Jun 16, 2006, 8:52:07 AM6/16/06

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Titus Edelhofer wrote:

> 2. 64-bit MATLAB handles matrices up to 16 GB of memory!

The dreaded Out of Memory error occurs primarily because of the 2^32
limit on addressable space, which is a 4 GB limit. (There are
further restrictions due to use of that space by the operating
system.)

On a 64-bit machine, the addressable-space issue arises not at 16 GB,
but at 2^64 bytes, or about 10^19 bytes! (That's 16 exabytes, I
think.)

Therefore, the more fundamental memory limitation goes back to the
machine's memory limit, amount of swap space, etc.

Titus Edelhofer

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Jun 16, 2006, 9:01:08 AM6/16/06

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Hi,
yes and no: the (lexicographical) array-index is (at least for R14, not
exactly sure for R2006a) a 32-bit counter, which limits a single
matrix to 2^31-1 elements.
But yes, you can have plenty of them, provided your memory is
large enough... ;-)

Titus

"the cyclist" <thecy...@gmail.com> schrieb im Newsbeitrag
news:ef39...@webcrossing.raydaftYaTP...

Eric Sampson

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Jun 16, 2006, 9:04:09 AM6/16/06

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I think what Titus was referring to was that the largest array size
(2^31-1 elements, at least for now) that you can create takes up 16
GB of memory if it contains non-complex double values.

Steve Amphlett

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Jun 16, 2006, 9:18:01 AM6/16/06

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This limitation exists in most 64-bit software that uses integers for
array indexing. Although you have 64-bit pointers, you still only
have 32-bit integers.

bern...@clarkson.edu

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Jun 16, 2006, 2:33:15 PM6/16/06

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if you can afford it, get a two processor system. 1) you can do other
things on the computer at the same time, and 2) you can run 2 copies of
matlab at the same time, doubling your productivity, if you could use
such a thing. I know I'd like to be able to run two simulations per
night. My license allows me to have two copies running simultaneously,
you'd have to check about your license. Sometimes I let my personal
laptop run a simulation in addition to the work machine, but it's half
the speed for the algorithm i use.

MATLAB isn't multithreaded, so the programs run need to be independent.
It might be possible to rewrite your simulation to work in parallel,
but the two copies can only communicate through files.

Antoine Godbille

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Jun 27, 2006, 12:04:25 PM6/27/06

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Hello,

I am running a simulation on a 64 bits AMD processor. My model is
implemented in Simulink. In Simulink ../configuration
parameters/hardware implementation, there is not the possibility to
choose a 64 bits implementation. Does it mean my simulation is
effectively limited to 32 bits ?

Many thanks in advance

Antoine Godbille

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Jun 27, 2006, 12:08:04 PM6/27/06

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I forgot to mention that I was of course running a 64 bits version of
Matlab.

Steve Amphlett

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Jun 27, 2006, 4:38:53 PM6/27/06

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You also forgot to mention why you thought you might benefit from a
64-bit version of Matlab.

da

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Steve Womble

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Aug 11, 2006, 1:10:56 PM8/11/06

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If you work with double precision (i.e. 64bit) floating point (dpfp)
intensive code, then you will find a decent speed up in the execution
of mex files compiled using a 64bit compiler running on a 64bit
platform running a 64bit OS. Using an Intel PD (and XP-64bit edition,
MS compiler) I get roughly a 1.5 to 3 times improvement over 32bit
execution of dpfp intensive code. The speed up comes from being able
to perform arithmetic operations directly on all 64bits in a single
clock cycle rather than taking several cycles to update a 64bit datum
which in 32bit systems needs to be broken down operated on in chuncks
and then recombined.

Note my experience of this is for using C based mex binaries, and not
Matlab itself of which I am not certain... Since historically in
Matlab everything is/was treated as a 64bit array, one may think we'd
see some improvement in execution times, but maybe this is less
relevant to recent releases.

Rgds,
Steve

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Aug 12, 2006, 1:13:09 AM8/12/06

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For #1 & #2, I agree with others: benchmark your apps. For my own
C++ code, I've gotten huge speedups with 64-bit code (esp. because
the compiler gets to play with double the number of general purpose
registers). I've gotten mixed results with m-files. Some are a
little faster, some a little slower in 64-bit mode. Be forewarned
that the bench script that ships with matlab weighs graphics
performance heavily.

The only real advantage of running 32-bit matlab is if you need to
use mex files that link to 32-bit-only 3rd party libraries. A single
process cannot run both 32-bit and 64-bit code. I've run into this
issue with some mex functions that use video codecs, most of which
aren't available (yet) in 64-bit.

An advantage of a 2-proc, 2-core system is that you can easily run
four Matlab sessions simulateously at full speed, *if* you buy enough
memory and if you are CPU-bound, not I/O-bound. You also have just
one machine to configure and maintain instead of 2 or 4. The
downside is that this can be a very expensive way to go, especially
if you have non-trivial memory needs. For example, if you want each
session to be able to access 2GB quickly, then you'll want to buy 8GB
of RAM. It's often cheaper to buy two single-proc, 2-core systems
with 4GB of RAM than a single 2-proc, 2-core system with 8GB.

The other possible advantage of increasing the number of cores
(beyond just being able to do other stuff with the machine) is that
you can apparently replace some of the core math libraries Matlab
uses with multi-threaded ones. This doesn't change the way Matlab
works, as seen by M-files, but for certain operations, it can give
more speedups with more cores. Search around if you're interested in
doing this (I haven't bothered trying it out yet).

Steve Amphlett

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Aug 12, 2006, 2:41:07 PM8/12/06

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It stikes me that not only has this thread been spammed to death,
it's also badly named. Should be:

x86 vs x86_64

64-bit computing per se is as old as the hills.

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