"With a 32-bit operating system, the maximum amount of addressable system
ram is 4,096 Kilobytes (4 Gigs). If you put 4 Gigs of RAM into a 32-bit
Vista PC, this is what you'll see under your system stats. There are
hundreds of explanations for this in as many different levels of tech-speak.
However, to put it in layman's terms--a 32-bit operating system can only
address up to 4096 Kilobytes of memory. That sounds fine in theory, because
that is the amount you have installed right? Well, this is where things get
a bit more complicated. 32-bit operating systems develop a 'memory hole' and
for those who have been around long enough, think back to the 286 days when
we were using DOS commands with the XMS managers to try and put device
drivers into extended memory, above the 1024 mark. Remember that 'hole' that
resided between 640 and 1024 that we couldn't put anything into?