re: How big a RAM can be used for a 32-bit OS
Wednesday, July 21, 2010 at 12:30 pm
Windows XP Annoyances Discussion Forum
Posted by MartinM
(7538 messages posted)
There is no general answer to your question - it depends on the precise 32-bit
system you are referring to.
The theory is simple:
2 to the power of 32 equals 4,294,967,296, that is to say about 4GB.
However the implementation of real-life systems is anything but simple.
There are techniques (eg PAE) to increase the amount of addressable space beyond
what you would expect from the number of bits in the address, as well as restrictions
(eg some address space is reserved for I/O devices) which reduce it from the theoretical
maximum. None of these are susceptible to formulaic calculations - you have to read
the specifications of the hardware (particularly the MOBO and internal bus specifications)
and software you are interested in.
As a real-life example, 32 bit XP could in theory address 4GB of RAM but in practice
it never uses as much as 2GB and installing any more is a waste.
There is a 3GB switch for XP but to most applications that makes little or no
difference !
Have a read of this for a start:
http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx
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