You just bought a shiny new computer and stuffed 4 gigabytes of RAM into it. You boot it and Windows only finds 3 gigabytes. What happened?

In an otherwise excellent article “Does Vista really need 4GB of RAM?” Fred Langa fails to mention that on most Windows machines you will not get access to the last gigabyte. This is a hardware problem running XP or Vista 64 bit editions will not solve this problem.

The problem the hardware reserves the last gigabyte for memory
mapped devices: Video cards, PCI cards, BIOS etc. So on most machines
Windows will only get to see 3GB of RAM and it will reserve the last
gigabyte for file caching.

So how do you get around this? You need a mother board that’s
designed to map your 4 Gigabyte of RAM above the memory mapped devices.
These are typically found in servers or high end desktops. Good luck
finding one a laptop that will solve this.

So before you go out and buy 4 gigabytes of RAM make sure that your motherboard will give you everything you paid for.

The best references: Jeff Atwood’s Dude, Where’s My 4 Gigabytes of RAM? and Ian Griffiths 3GB or 4GB – a ‘Virtual’ Memory Upgrade

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