the 4GB limit is the "virtual" memory limit. It's divided into two parts, 2GB for kernel use, 2GB for app use. Each app gets its own 2GB, but all must share the 2GB kernel space. So technically, each app has exclusive access to 2GB only.

These issues start to matter when running Terminal Server.

The only time the additional RAM is of tremendous benefit is when you've got Photoshop, Vegas, and AE or Boris open. It also involves a registry mod, if I remember right.
FWIW, Vegas 6 seems to run better with less RAM allocated, even though it makes sense to allocate more.

You can increase (In XP Pro only) the amount of RAM (physical + virtual max is 3GB) your PC can use per application.

You have to edit the boot.ini, I'll look up exactly what needs to be modified and post it here when I get a chance.

Just out of curiosity, for those with 4GB installed, what does Windows report as available?

The reason I ask is that I recently had to write up a service advisory about systems not being able to address a full 4 GB of memory. Turns out that the system reserves quite a lot of the top address space for devices and those addresses aren't available for memory. IBM had a similar document for their server customers and they were saying that somewhere around 750 MB of the last GB would be unaddressable.

Think of it like having 4000 telephones but only 3200 phone numbers available.

This is for 32bit systems. I've not actually seen a system running 4GB but I'd love to have a screen shot of something like "System Properties" showing this phenomena.

Rob Mack

Folks, if you want to read up on the gory details of the os at work, look up Microsoft's TechNet or the XP Resource Kit. Goes into far more detail.

Mack350:
I can't give you a screen shot but I can tell you what happens when you insert 4 gig into the Intel 875 board. XP will say that only 3304 gigs memory installed. Also all hell breaks loose as timeline playback in V5 goes bananas with the sound. Intel bios says everthing is just wonderfull and everthing works properly. This is with the P-33 bios.

JJK

Thanks. That's what I was looking for. Kind of surprised that Vegas freaks out though.

The deal is that any 32bit system uses a finite pool of addresses. Those addresses can be applied to any hardware object, be it a PCI card, BIOS Shadow ROM, or a block of memory.

If there were no other hardware in the system (which is impossible) then there would be just enough available addresses to use al 4.0 GB of memory. But since a pretty substantial block of addresses must be used for other hardware, some of the memory is left in limbo.

If you had only 3.0GB or less installed then it wouldn't be a problem. The addresses being used are at the top of the pool. You could install a matched pair of 1 GB DIMMs and a matched pair of 512 MB DIMMs and save a few bucks.

(I'm just practicing explaining it here. I have to explain it to support techs for a big company. Please humor me.)

Here's another analogy. You live on a very long street and each lot has a mailing address. However, the city didn't think that the lots at the far end of the street would ever have houses on them so they used up all the mailing addresses down there for other things. Now time has passed and those lots were filled but they'll never get any mail because they don't have addresses.

That's what's up with that last chunk of RAM.

If you want to send me a screen grab of the system properties window, send it to rmack350 at sbcglobal dot net. Just select that window and press <alt+PrintScrn> to get a copy of that window onto the clipboard. From there you can paste it into MSPaint and make a gif or jpg file out of it.

Thanks,

Rob Mack