I just built my new computer. I boot up and after it posts boot, it read 4096kb ram.

I'm using OCZ Reaper HPC ed. CAS 4 --> 2 x 2gb
When I display system properties it says I have 3gb ram, why not 4?

appreciate your help. I'm using Windows xp sp2.

A 32-bit OS will not utilize all 4GB of RAM. It's a bit complicated but there are plenty of threads out there on this that will explain it far better than I can.

-mcg

Like he said if you use a 32-bit os it will only address up to 4GB of ram.(including video card i believe) so if you got a 512 mb video card and 4 Gb of system ram it will typically show 3.5 GB of system ram after subtracting the ram from the card. thats my basic understanding of it.
-crowheart

Thanks guys...not sure why I never ran across this before. That kinda sucks...maybe I should upgrade to Vista...but I was under the impression Windows XP was better for gaming and receives better benchmarks. Plus I heard there were some issues with crossfire + Vista 64-bit.

*shrug*

No longer. Vista 64 is king these days.

The whole 4Gb of addressing is a bit more complicated than presented here, but basically your operating systems limit will always be a bit less than stated. The figure for 32 bit Windows can go as low as 2.6Gb, although usually it falls between 3 and 3.5.

In 32 bit Windows operating systems, the total addressable space available is 4GB. If you install a total of 4GB worth of RAM, the system will detect/use/display less than 4GB of total memory because of address space allocation for other critical functions, such as:

- System BIOS (including motherboard, add-on cards, etc..)
- Motherboards resources
- Memory mapped I/O
- Configuration for AGP/PCI-Ex/PCI
- Other memory allocations for PCI devices

Different onboard devices and different add-on cards (devices) will result of different total memory size. e.g. more PCI cards installed will require more memory resources, resulting of less memory free for other uses.

This limitation applies to most chipsets & Windows XP/Vista 32-bit version operating systems. Again, this is a limitation of the Operating System not having enough address space to allocate to the system *and* the RAM. Not allocating address space to devices renders them inoperable. Not allocating addresses to RAM simply results in the unaddressed section not being used in an otherwise fully functional computer. Therefore the OS designers assign RAM last.

We can have long debates about mathematical fundamentals and discussions about why the original Windows designers couldn't allocate the full theoretical max of 36 bits of address space so that users today would be able to use more resource. But at the end of the day, the designers and engineers 'Didn't Then'. So we 'Can't Now'.


If you install a Windows operating system, and if more than 3GB memory is required for your system, then the below conditions must be met:

1. A memory controller which supports memory swap functionality is used. The latest chipsets like Intel 975X, 955X, Nvidia NF4 SLI Intel Edition, Nvidia NF4 SLI X16, AMD K8 and newer architectures can support the memory swap function.

2. Installation of Windows XP Pro X64 Ed. (64-bit), Windows Vista 64, or other OS which can provide more than 4GB worth of address space.



Note: According to the latest Change Log published by Microsoft, Windows Vista 32bit SP1 will display the installed amount of RAM. This is a display change only.