Windows Vista 32-Bit cannot by default detect more than 4 GB of physical RAM. This limit is set because beyond 4 GB, many 32-Bit operating systems lose efficiency in managing memory.
You can manually bump this up however if you have a machine with more than 4 GB of memory and only have access to the 32-Bit versions of Vista.
Click on the start pebble and in the search area type:
Don’t hit the enter key however. You’ll see that after you type cmd in the search box, cmd.exe will appear in the programs list. You’ll have to open this as an administrator. To do this, right click on it and choose Run as Administrator.
Once your command prompt is open, type:
BCDEdit /set PAE forceenable
BCDEdit is a boot configuration editor for the command line. Using the above command you’ve just enabled Physical Address Extension (PAE) which can address memory larger than 4 GB.
The 64-Bit versions of Vista can support between 8 GB and 128 GB of RAM depending on what version you get your hands on.