So you just plugged in that brand new system with 4GB+ of memory or installed some more RAM in your current system. You go to check your System Information (Vista) or System Properties (XP) and it only reports 2.2 to 3.3 GB of memory. Unfortunately that’s normal if you’re running a 32 bit version of Windows Vista or XP.
32 bit means 2 to the power of 32 which is commonly denoted as 2^32. For those of you that were not very good at math in school, it looks like this:
2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2x2×2 = 4294967296 bytes
4294967296 bytes / 1024 bytes/1 kilobytes = 4194304 kilobytes (kB)
4194304 kB / 1024 kB/1 MB = 4096 MB
4096 MB / 1024 MB/1 GB = 4 GB
Therefore a 32 bit OS can only support up to 4GB of RAM.
Some of you thought you had done your homework when you read up that Windows Vista/XP 32 bit supports up to 4GB of RAM. Unfortunately, Windows Vista and XP reserve higher memory addresses for other devices in your computer. An example in Microsoft’s Knowledge Base Article 929605 explains it well:
”if you have a video card that has 256 MB of onboard memory, that memory must be mapped within the first 4 GB of address space. If 4 GB of system memory is already installed, part of that address space must be reserved by the graphics memory mapping. Graphics memory mapping overwrites a part of the system memory. These conditions reduce the total amount of system memory that is available to the operating system.”
Further reading on the 4 GB RAM limitation of 32 bit Vista:
http://support.microsoft.com/kb/929605/en-us
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