The Tale of the Lost 1GB of RAM

I was navigating through the Dell website, and using their computer customization service I added 4GB of Ram to their laptop when I realized whether Windows Vista would have problems with that much RAM. Obviously it should have no problems but I still researched to be sure.

Then I found this — The 3GB-not-4GB RAM problem. Wow, I did not imagine that was indeed going to be a problem on Windows Vista.

In an excerpt:

If you are running 32-bit Windows, you must live with it. You will not ever see all 4GB of RAM you’ve paid for.

If you are running 64-bit Windows, you may have to live with it. Depending on your motherboard’s chipset, your system may support memory remapping. If so, you will be able to use all 4GB of RAM.

Detailed:
Due to an architectural decision made long ago, if you have 4GB of physical RAM installed, Windows is only able to report a portion of the physical 4GB of RAM (ranges from ~2.75GB to 3.5GB depending on the devices installed, motherboard’s chipset & BIOS).

This behavior is due to “memory mapped IO reservations”. Those reservations overlay the physical address space and mask out those physical addresses so that they cannot be used for working memory. This is independent of the OS running on the machine.

At least we can all be cautious on being to ambitious on our computer specs.

The rest of the explanation is found here.