Maximum program sizes in Vista 32 and Vista 64

[dfumento]

Because Windows is a virtual memory OS, the process limit is based on
virtual address space, not physical RAM. The physical RAM limits are tied to
the OS itself.

32-bit versions of Windows XP and Vista are limited to 4 GB of physical RAM,
although most motherboards & BIOSes don't really expose the full 4 GB. The
best I've seen is 3.25 GB physical RAM visible with 4 GB installed. 64-bit
versions of Windows XP and Vista support more, and it depends on the exact
SKU as to how much, but ranges from 4 GB to 128 GB or more.

A standard 32-bit process can address up to 2 GB of virtual address space.
Typically this means at most 2 GB of physical RAM, although a fair bit less
due the fact that virtual address space is used for things other than just
memory allocations by the application.

A Large Address Aware 32-bit process can get up to 2 GB, 3 GB, or 4 GB of
virtual address space depending on the OS and configuration it is running
on. On 32-bit Windows, such applications can only get 2GB unless the system
has been booted with a special boot option. At most such a special boot
option can give the process up to 3 GB, although this limits the OS to 1 GB
which can cause stability problems. On 64-bit Windows, a Large Address Aware
32-bit application can get up to 4 GB without any special boot options.

A 64-bit native process running on a 64-bit OS can address up to 8 TB of
virtual address space in current implementations. Future hardware can extend
support from the current 44 address lines up to 64 over time.

I did a presentation for our GameFest event on the issue of VA space and
memory you might find useful:

http://download.microsoft.com/download/ ... 0Bytes.zip

There are also specialized 'windowed' extensions you can use to address more
physical RAM from a 32-bit process within the 2 GB virtual address space,
but using them can be tricky.

--
Chuck Walbourn
SDE, XNA Developer Connection