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Any reason NOT to run 32 bit apps on 64 bit Windows?

 
 
Jim
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      09-22-2006
Scenario:

I'm implementing servers that will run a new application that consists of
the app itself and a database. They're all X64 CPU boxes and there are 64
bit drivers for all my hardware. My company's developers are writing the
app from scratch. I'll be running 64 bit Windows Server 2003 R2 and 64 Bit
SQL Server. The app won't require more than 2 GB of memory and won't
otherwise benefit from X64, but that's what's available from my hardware
manufacturer these days, so it's an X64 box. So, the questions:

1) Should I run 32 bit or 64 bit Windows on my app servers? Why?
2) Should the app be written so that it can run on 64 bit Windows or just 32
bit?

I ask the questions because I'd like to standardize as much as possible.
All machines are X64 machines, I'd like to standardize on X64 Windows, but
the article at http://insight.zdnet.co.uk/0,39020415,39281436,00.htm says

"In fact, there can be a slight performance decrease caused by the switch to
a 64-bit processor, because the larger memory address pointers take up twice
as much room in the cache."

There are no benchmarks to backup that statement and what "slight" equates
to is questionable. Does anyone know of any downsides to running 32 bit
apps on Windows 64 bit (performance or otherwise)? Is performance really
degraded, and if so, by how much (i.e. do you know of any real benchmarks
done or is this just a theoretical statement)?

Thanks,

 
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John Barnes
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      09-23-2006

IMHO

> 1) Should I run 32 bit or 64 bit Windows on my app servers? Why?


If you are going to need any 64-bit applications such as 64-bit SQL you will
have to run a 64-bit os

> 2) Should the app be written so that it can run on 64 bit Windows or just
> 32 bit?


If the application will NEVER need to be run on a 32-bit os, write it so it
will run native 64-bit
>
> I ask the questions because I'd like to standardize as much as possible.
> All machines are X64 machines, I'd like to standardize on X64 Windows, but
> the article at http://insight.zdnet.co.uk/0,39020415,39281436,00.htm says
>
> "In fact, there can be a slight performance decrease caused by the switch
> to a 64-bit processor, because the larger memory address pointers take up
> twice as much room in the cache."


The size of the cache for direct addressing doesn't slow anything. The fact
that it has to call the emulation layer does, but everything posted here
suggests that the difference is infinitesimal.


>
> There are no benchmarks to backup that statement and what "slight" equates
> to is questionable. Does anyone know of any downsides to running 32 bit
> apps on Windows 64 bit (performance or otherwise)? Is performance really
> degraded, and if so, by how much (i.e. do you know of any real benchmarks
> done or is this just a theoretical statement)?


see above.
>




 
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James Robertson
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      09-25-2006
The more CPU intensive your application is, the higher the chances are that
you'll see a speed increase when targeting x64. I've seen speed increases
of 23% simply from recompiling for x64 native. Primarily due to the larger
register set available in long mode.




"Jim" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Scenario:
>
> I'm implementing servers that will run a new application that consists of
> the app itself and a database. They're all X64 CPU boxes and there are 64
> bit drivers for all my hardware. My company's developers are writing the
> app from scratch. I'll be running 64 bit Windows Server 2003 R2 and 64
> Bit SQL Server. The app won't require more than 2 GB of memory and won't
> otherwise benefit from X64, but that's what's available from my hardware
> manufacturer these days, so it's an X64 box. So, the questions:
>
> 1) Should I run 32 bit or 64 bit Windows on my app servers? Why?
> 2) Should the app be written so that it can run on 64 bit Windows or just
> 32 bit?
>
> I ask the questions because I'd like to standardize as much as possible.
> All machines are X64 machines, I'd like to standardize on X64 Windows, but
> the article at http://insight.zdnet.co.uk/0,39020415,39281436,00.htm says
>
> "In fact, there can be a slight performance decrease caused by the switch
> to a 64-bit processor, because the larger memory address pointers take up
> twice as much room in the cache."
>
> There are no benchmarks to backup that statement and what "slight" equates
> to is questionable. Does anyone know of any downsides to running 32 bit
> apps on Windows 64 bit (performance or otherwise)? Is performance really
> degraded, and if so, by how much (i.e. do you know of any real benchmarks
> done or is this just a theoretical statement)?
>
> Thanks,



 
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