Originally Posted by Colossous 
Hi Agent, From what i understand (and i may be wrong as there's a lot of confusion on the subject - maybe time for a sticky he he !!?), 32 bit os's can only deal with 4gb max memory in there registers so if you have 512mb on your graphics card this is part of the 4gb total ?
Hi
There will be a bit sticky on these kinda things once im back modding in a few weeks
You are partly correct, but its no the OS that deals with addressing. All low-level addressing is done at the BIOS level, not OS.
Most (all?) 32bit OS's do have a limit of 4gb (without some form of PAE addressing - see below), but it will only see 4gb if 4gb of addressing space for the RAM has been passed on to it (the BIOS bit above
)
Originally Posted by Colossous I recently built a twin Opty server for a guy editing video which had 4gb RAM and XP 32 bit would only recognise 3gb (which makes a nonsense of what i said before as the Quadro card was only 512mb RAM !) and so we put 64 bit on and it recognised the 4gb with no problems. For educations sake could you point me in the right direction if you know of a good factual thread or article on the subject ? Thanks.[/COLOR][/I]
As mentioned above, I will write one in a few weeks - I don't know of any off the top of my head sadly
The reason for this situation is fairly simple. The 32bit OS can only use 32bit addressing from the BIOS. A number of these are memory mapped IO reservations, which 'eats' into your avaliable RAM for a 32bit OS.
On the motherboard that you had used, it either didnt have (or wasnt on) PAE.
PAE allows the BIOS to address up to 64gb in a 32bit environment (it uses 36bit addressing IIRC).
Also, windows needs specific tweaks to get it to work properly in 32bit mode - the /pae switch in the boot.ini file. Its not as simple as plugging it and and playing, like with normal RAM, sadly
Even if the motherboard did support PAE, without this tweak, it will not work.
Hope that helps - Its a bit more confusing than it needs to be