32bit program running on 64bit OS Memory Consumption

Question

We have a windows server 2008 R2 32G memory machine, this is obviously a 64bit OS. And we installed XAMPP 32bit version, with 32bit MySQL and PHP. Then we host an webmail system written in PHP on it. My question is : will those 32bit MySQL and 32bit PHP consume more than 4G memory of the OS ? Do We have to install 64bit MYSQL and PHP to achive this result ?

Thank you

Answer 1

Based on the x86 architecture instruction set, a software compiled in 32 bits won't ever be able to allocate more than 4GiB since they won't be able to access this memory directly. As they use 32 bits to represent memory addresses, and since 2^32 = 4GiB (rounded), they won't be able to represent any address further.

On a side note, a software could indirectly work with more than 4GiB of memory on a 32 bits system by using PAE, but the software must be explicitly developed to use this.

You need the 64 bits version of every software and their libraries otherwise you won't be able to use more than 4GiB directly, even if the OS recognize all your memory.