RAM usage in 32- and 64-bit Windows operating systems.
Can you use 8 GB of RAM in Windows XP? How about in Vista? Well, it depends on the architecture of you operating system.
32-bit operating systems only have enough memory addresses built into the architecture to recognize 4 total GB of RAM. Unfortunately, this cannot all be addressed by physically installed RAM. The motherboard, video card, DSP cards, and other similar devices in a computer system have their own RAM built in. These devices are addressed prior to Windows filling up its available space with installed RAM chips. Here’s an example of what to expect. Suppose a motherboard has 64 MB RAM, a video card has 256 MB RAM, and a DSP card uses another 512 MB RAM. This system also has four 1-GB RAM sticks installed. How much will Windows see?
The 4 GB RAM make up 4096 MB. The RAM from the other devices (512 + 256 + 64) will be addressed first. This 832 MB is addressed first, and subtracted from what Windows can see of the 4096 that is installed. So, Windows will only be able to use 3.25 GB (3,264 MB) of the installed RAM. This is the value that you will see in Windows’ System Properties page.
This process is the same for all 32-bit editions of Windows, including:
* XP Home
* XP Professional
* XP media center Edition
* All 32-bit Vista editions
64-bit operating systems, however, have enough theoretical space for 17,179,869,184 GB, or 16 exabytes (EB) of RAM. However, practical limitations have been applied to most OS’s, so that they recognize a predetermined maximum. This number is well over the 4 GB of a 32-bit OS. Here’s a breakdown of current versions:
* XP Professional x64: 128 GB RAM
* Vista Home Basic: 8 GB.
* Vista Home Premium: 16 GB.
* Vista Business: 128+ GB.
* Vista Ultimate: 128+ GB.
* Vista Enterprise: 128+ GB.
Similar addressing issues will apply in 64-bit OS’s as in 32-bit ones. So, if you have 128 physical GB RAM installed in XP x64, several hundred MB will not be availble due to hardware addressing issues. But, the remaining 127.25 GB RAM will be.
Most motherboards (current as of the writing) support a maximum of 8 or 16 GB RAM. Very few support 32 GB or more. As technology improves, however, the operating system will be able accommodate improved hardware.
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