**** WARNING **** GEEK ALERT **** WARNING ****
do not read this post unless you:
a. have a vague interest in computer hardware, OSes etc.
b. want a migraine headache
**** WARNING **** GEEK ALERT **** WARNING ****
after some serious (and somewhat confusing) reading... I have discovered the following...
32bit OS's can 'address' up to 4gigs of memory... unfortunately, as things like memory mapped video and device drivers (DMA-mode) etc. also require a memory 'address', you get the following situation:
|---1gig---||---2gig---||---3gig---||---4gig----|
|----------3.5gig RAM addresses-------||-HW-|
ie. your hardware uses some of the 4gig memory address space. Its not using your RAM as such, but its occupying an address space, so your RAM cannot be fully used, as XP cannot assign an address to it
Now prior to XP SP1 and SP2, apparently you could throw in a /PAE switch into boot.ini to enable "Physical Address Extenstion" which would then do this:
|---1gig---||---2gig---||---3gig---||---4gig----||----------...
|----------3.5gig RAM addresses-------||-HW-||--RAM--|
ie. it would allow windows to have more than 4gigs of address space, so it could then get access to all your RAM, by extending the address space (not sure exactly how this works
) and pushing the remaining bits of RAM into a higher address space.
Unfortunately, as far as I can gather, sometimes the hardware would actually be pushed into the higher address spaces and there were too many buggy drivers written etc. which did not cope well with this setup and caused too many system crashes and other problems, so M$ removed the functionality to try to ensure system stability.
The upshot of all this is that I am looking into 64bit OS's as they do not have this issue... I already have XP 64bit, which I will try putting into a dual boot tonight... and looking at our MS Volume License Services, our company is allowed Vista Business 64bit, so I will probably nab that on monday
I'm kinda concerned, as I have seen people commenting on lack of 64bit drivers and gaming on a 64bit system does not seem to be too common... I'll let you all know how I get on...
cheers,
HCP
