Ok, I know about the /3GB line in the boot.ini

So, as I now am gonna install 4GB RAM on my new mobo AND my new 460 GTX has 1GB RAM what memory is gonna be used? Is the graphics card memory included in the total. Yeah I have XP Pro 32 bit and keeping it for awhile longer.

The way I understand it, that 1GB on the graphics card is included in the total used by 32 bit XP. So, what am I gaining over what I had with 2GB of memory and a vid card with 1MB?

Can somebody simply explain this to me???

with the /3gb line

4GB is your bottom line.

Minus System resources first.
-1GB VRAM, 3.0GB
-Any Sound or Lan memory

Whatever is left will be available for system RAM,

So prolly 3GB of the 4 GB will be used by windows.

I thought the /3G line limited Windows to 1GB and the other 3GB are now for use by processes and applications, at least that's the way I read This!

I guess the 1GB vid card wasn't needed....and is really a waste of cash when using XP without the /3G command line, which only works with XP Pro.

The whole thing is actually rather confusing. So, an Attempt to explain.

the /3GB changes windows memory management a lil, but does not remove the 4.0GB (4096MB) Limit from the 32 Bit OS. Where the O/S would normally divide Availible memory address evenly between Kernel and Applications. the /3GB overrides that and sets 1GB Address to the kernel and the rest goes to the applications and whatever else.

For Example: In a 32-Bit 4GB environment,
Windows usually would set 2 GB for Windows, and that leaves 2 GB for Applications.

Now if your Running a 1GB GFX Card, your knocking 1GB off of the Memory Address at boot up. (-1024 MB)
So you have 3 GB of address (3072 MB), Which means Windows Kernel gets 1.5GB (1536 MB) GB and Applications Get 1.5GB.

the /3 switch limits windows to 1GB (1024MB) Address space for the system kernel, thus giving you back .5GB (512MB) for General Applications. So 1GB would be for the Kernel and anything left over in the 4GB Memory Address would be for the System.

Even So the /3GB switch is only availible in Pro Version of XP. And basically it is compressing and limiting the O/S's Kernel size which may or may not be a good thing.


Still the Bottom Line is the 4GB Max Physical Address Space for 32-Bit.

This Address space is used for Every device. Not Just the GFX and System Ram.

When You Boot up, the Memory Address is assigned to Graphics Cards, System ROM, CPU Cache, LAN, SCSI, SATA, IDE, FLOPPY, USB Devices, and I/O Ports. (which is why I dont enable my i/o ports in the bios, no one needs LPT, Parallel, Serial, etc).

for 32 Bit, . You Might Get 2.5 GB (2560MB) usuable after the GFX Card, Mainboard BIOS (Usually 8MB), Sound Card, LAN, and all the I/O Ports take their share of the 4 GB Address during boot up. Which leaves you with 2.5GB of Address for the System RAM (2560 Mb) Windows would Split it 1280 for the Kernel, and 1280 for Applications, which case the /3 Switch would only give you back 256 MB of System Ram.

Ahhh, makes more sense now.

There's a post over at the A-10 forum where these guys are saying that high performance graphics cards are wasted on 32 bit systems. But if windows allocates the 1GB to the vid card first as you say, then it's just leaving me a little less then 2GB for app's and processes, which is still a big improvement over what I had with only 2MB installed. Good to know my new 460GTX 1GB wasn't a waste of scarce cash.

Thanks Skate

Don't use /3GB. It's no benefit at all unless you're using an application built with the LAA flag (not common) and the 32 bit windows kernel is NOT meant to operate under normal circumstances with only 1 GB of address space available. It's very likely to have an overall negative impact on your stability.

If you're concerned about not getting the benefit of all the memory in your system, upgrade with Win7 x64. That's the bottom line.

Well I have been told by some folks over at the DCS A-10 that it's the only way to get the sim to work with 32 bit XP.

Thread Link

I'm not very familiar with DCS A-10 so I can't really comment. All I know is that /3GB has never been recommended for general use. Like I said, you may sacrifice system stability if you use it.

I will say though, if DCS A-10 really does need more than 2GB of memory to run (presumably the reason they would say it required the /3GB flag), it was a very cheap move by ED to even release a 32 bit executable.