Windows XP Memory restriction.

[Paramartha]

I have decided upon an Asus P5Q-E board, and a Q6600 processor, as money is an issue, and this will be a nice upgrade from what I currently have. But I am a bit confused about Windows XP memory restrictions. I understand that XP 32-bit, doesn't recognise 4GB of memory, is this correct? In the specifications for the motherboard, here is what was said about memory:

When installing total memory of 4GB capacity or more, Windows 32-bit operation system may only recognize less than 3GB. Hence, a total installed memory of less than 3GB is recommended.

It says at the bottom that less than 3GB is recommended. Wouldn't that mean 2GB? Would my system benefit if I threw in 3GB (3x1GB)? I was once told that memory should be installed in pairs. Does that mean I shouldn't use 3 sticks of 1GB memory? And according to what they said about their memory, should I buy DDR2 1200MHz memory and expect it to work okay?

[Pageous]

A good way to see this is to open up Device Manager, view the list as "devices by connection", and in the ACPI tree, you'll see everything that's connected to the PCI bus.

Observing the memory allocations by individual devices is interesting to look at, too... those ranges of addresses generally represent where, in "real" memory, according to the CPU's addressing (i.e. not an OS's process-level virtual memory allocation), the device lives (DMA buffers, for example). The problem with this is kinda like back in the "640k is enough for anybody" days, whereby on a machine with 1MB memory, that memory above 640kb was reserved for devices and other system things, and wasn't actually available to your apps.

Basically we've doubled the number of bits and hit the same sort of problem again. That's why Windows XP SP2 is limited to ~3.2 GB memory. It isn't a precise amount because, like DriverGuru said, it depends on your devices. Where they end up plopping themselves down in memory can impact some things. PCI Express takes up a chunk of space... IIRC it's 256MB per card, so you could find yourself with 2.75GB of memory on a 4GB system if you have a pair of PCIe cards running in SLI.

That said, some new chipsets support a "memory swap" option so that the physical memory hidden underneath the address space that's been set aside for PCI(e) devices can be accessed by the CPU and thus the operating system.

It's really a lot more complicated and headache-inducing than that, but that's the gist of it. And, that's why I program in .NET for a living.

[Arkad]

XP 32 bit only picks up that much no matter what... if you want the full 4GB, you need a 64bit OS

Just because the mobo supports it DOES NOT mean that the OS supports it

[Zane]

You can put 4 GB of RAM into XP Home. BUT, you will not see all 4 GB. You will seem 4 GB MINUS whatever is set aside for hardware (PCI devices, etc.). This probably turns out to be somewhere between 2.5 and 3.5 GB in most cases.

Is that a little more clear?