4GB RAM and /PAE + /3GB in Win2000 Pro?

[tomasz86]

I wonder whether there are any benefits from using /PAE and /3GB switches with 4GB RAM in Windows 2000 Professional. Without PAE system sees 3.75 GB.

[allen2]

You don't need /PAE as it should only be used when memory > 4GB for edition that support it.

/3GB might be needed if you're using application that need more than 2GB of memory.

[dencorso]

Read this sticky, and the links pointed therein.

[cluberti]

+1 - PAE is for RAM over 4GB (and *only* works in 2000 Advanced server and Datacenter editions!), and /3GB has absolutely NOTHING to do with RAM.

[tomasz86]

O.K. I understand.

How about Win2K Advanced Server with 4 GB RAM? Without PAE it sees only 3,4 GB but with PAE enabled I can use all of the available 4 GB. It it better to use PAE in this case?

[cluberti]

That's up to you. /PAE adds some memory manager overhead, but if you need the memory, then you'll have to make that decision. You don't need the /3GB switch unless you 1. have an application that is compiled /LARGEADDRESSAWARE and needs access to the additional 1GB of virtual address space that /3GB provides (remember that virtual address space has nothing to do with RAM), and 2. don't mind running your system at dangerously low levels of PTEs. You can use the /USERVA switch to modify the range of that 3rd GB of VA to give some of that kernel virtual address space back to the kernel (and thus increase the size of paged pool slightly and get back more PTEs), but you really want to avoid that route unless it's absolutely necessary.

Given that you were first asking about doing this on a 2000 Workstation, I'm guessing you really don't need /3GB, and probably don't really need /PAE to get access to the last 512MB or so of RAM on the system. It might make more sense for you to consider XP x64, or better, Vista or Win7 x64 if you really need access to more RAM on a workstation system.

[tomasz86]

Actually I did a test using Win2K Advanced Server and:

1. no PAE, no 3GB

2. PAE, 3GB

3. 3GB, no PAE

4. PAE, no 3GB

5. Utilising 4GB RAM fully

Full test (in Polish)

I happen to open a lot of pages containing many large images and my browser usually crashes when reaching the 1,5 GB value. With 3GB... well I can open more websites at once as browser doesn't crash until 2,5 GB

Edited September 24, 2011 by tomasz86

[cluberti]

From what I understand, Firefox 4.x builds are compiled LARGEADDRESSAWARE, but 3.x and older are not. If you're running FF 4.x, that would make sense. If you are running anything older than that, the /3GB is probably allowing something else to expand, but it won't be Firefox. I can't argue with the results, but again only FF 4.x 32bit builds are compiled LAA, so unless you're using that the /3GB switch is not helping Firefox specifically.

[tomasz86]

It was FF 4.0 but it's exactly the same in case of Opera 11 - it can eat up to 2.5 GB memory before crashing.

[cluberti]

Opera 11 is also compiled LARGEADDRESSAWARE, so both browsers (Firefox and Opera) will be able to use more than 2GB of VA, which will likely show up as more RAM usage before they crash. Good to see you've at least found something that helps.