Windows 7 - 4gb RAM installed, sometimes showed 2gb usable

The irony here is: Scotteq addressed the limitation of your machine while he was harping on and on.

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.

The issue here is people using 32 bit operating systems when they have enough devices that they have run out of address space.

In a computer all bytes in the memory system need a unique name. This is called an address. For example, if you have 2 GB of main memory, then there are 2147483648 bytes of RAM in your machine, each of which require an address for the operating system to communicate to it. To give these all an address you need 31 bits to do it. Now, if/when you have 32 bits, you can name 4 GB (2 bytes to the 32nd power = 4GB).

This is why the total addressable space available in a 32 bit OS is 4GB – the OS runs out of addresses and cannot communicate/locate any more bytes of memory because of that.

You may think ”Hey, 4GB of address space… 4GB of RAM… What’s the problem?”

The problem is that memory isn’t the only thing needing an address. 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.


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.

Hello;

I am also having the exact same issue. I built my PC last week & installed Windows 7 on my PC a few days ago. All Microsoft Updates were installed. I had the full 6GB of RAM available following the OS install. All drivers were installed and the RAM usage was 6GB. After around 3 days, I have looked at the properties of the computer again & now the status of RAM is 6GB (2GB usable). I checked every day for the past three days and it was set to 6GB. Only this evening when I checked, it was set to 2GB usable.

I have Windows 7 64BIT installed on the PC. My HD setup contains two (2) 500MB Sata HD's with a RAID1 configuration. My PC also contains a 1GB PCI-E Video card. If it were hardware using 4GB of the system memory, as soon as the PC was built & all drivers were installed, the RAM usage would have specified 2GB usable following the installation, not three days later. I have a feeling, in which I could be wrong, that this is yet again, another Microsoft bug that Microsoft will have to answer for...