It isn't as much of a mystery as people make it out to be. By default, on a 32-bit system with 4GB of RAM, 2GB is available for user space, and 2GB is reserved for exclusive use by the kernel--which would include kernel mode drivers. You are also correct in that some of this upper space is reduced by various system devices, some of which might not make much sense. The reason that systems differ is because of varying chipsets, their maximum addressable memory, the ability of the chipset and BIOS to remap memory above system-reserved spaces, and, of course, the devices installed.
Using the /3GB switch will shift the division to 3GB of userland and 1GB of kernel memory, but keep in mind that each individual 32-bit address will still be limited to 2GB of memory unless it was compiled with LARGE_ADDRESS_AWARE. It gets much more complicated when you're using PAE (Physical Address Extensions) and AWE (Address Windowing Extensions), but that realm is only relevant if you're running Server Enterprise or better. > -----Original Message----- > From: [email protected] [mailto:hardware- > [email protected]] On Behalf Of Winterlight > Sent: Friday, September 18, 2009 1:00 PM > To: [email protected] > Subject: Re: [H] More than 4GB of ram and VM question > > This is not how I understand it to work, not that there seems to be > any kind of consensuses on this, but I read in Maximum PC that 32 bit > supports 4GB of RAM addressing. You start out with 4GB of RAM and > then windows starts knocking off for addresses already used by your > video card, your network card, whatever. This is why some people show > 3.2GB some, just 3GB. To add to the confusion, Maximum PC has > reported that MS has stated that windows can actually use some of > that undressed RAM for things such as drivers. > > > At 07:24 AM 9/18/2009, you wrote: > >Hello Brian, > >32-bit is really locked to 3GB of RAM, it's just Windows is reporting > the > >3.6GB of RAM. > >
