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How much ram do 32 bit programs have access to?

Last response: in Memory
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August 29, 2009 5:39:43 AM

I was wondering because I upgraded to win 7 64 bit after i lost my hard drive. Most of the programs i use have installed in the x86 program filles folder. right now, i believe, the only 64 bit program i have installed is adobe photoshop. Does it matter, what the program is natively will i still see the use of my 6 gigs of ram if i am mostly using 32 bit programs.
a b } Memory
August 29, 2009 6:25:08 AM

32-bit programs can only address a maximum of 4GB of memory in a 64-bit OS (they can only access 2 or 3GB of memory in a 32-bit OS). So a single 32-bit program won't be able to use all of your 6GB of memory.

But you will be able to, for example, run five 1GB programs at once and have them all fit into memory. And even if you're not running that many programs the extra memory will still be used for file caching.
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August 29, 2009 7:20:09 AM

thanks thats exactly what i was wondering.
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a b } Memory
August 29, 2009 7:25:55 AM

Are you sure about that? A 32bit windows OS has enought address space for 4GBs of ram, but each program is limited to 2GBs. The 3GB swich I believe limits windows to 1GB of space, but I don't think the extra GB goes to a singloe program. I don't know of any program limit in win x64.
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a b } Memory
August 29, 2009 8:14:21 AM

4745454b said:
Are you sure about that? A 32bit windows OS has enought address space for 4GBs of ram, but each program is limited to 2GBs. The 3GB swich I believe limits windows to 1GB of space, but I don't think the extra GB goes to a singloe program. I don't know of any program limit in win x64.
Are you asking about whether a 32-bit program can really access all 4GB in a 64-bit OS? The answer is yes, if the program has the "Large Address Aware" flag set (note this is NOT the same as PAE). See: this MSDN article
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August 29, 2009 9:54:01 AM

interesting....How do you set the large address? is it just entering the comand in the shortcut?
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a b } Memory
August 29, 2009 10:25:18 AM

So for future reference, in win x64, each 32bit program can use up to 4GBs of ram, and only 2/3GBs if using 32bit. Thanks for the link.
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August 29, 2009 2:47:49 PM

decen said:
interesting....How do you set the large address? is it just entering the comand in the shortcut?


The exefile must be altered. Editbin from Microsoft can do it. There is a small risk to it, if the developer of the application hasn't set it already. There is a small risk that it will crash when it tries to access memory above 2G - depending on how it is programmed.
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