What are the Ignored and Avail bits in the page directory ?

[matan]

http://wiki.osdev.org/Paging

In this article they specify the PDE format and explain the various flag bits.
but they don't give an explanation to what bits 9 to 11 do !
They are just named `Ignored` and `Avail`

Can someone shed some light on this ?

[iansjack]

As it says, the processor ignores these bits. So they don't do anything unless you choose to use them and define your own meaning.

[linguofreak]

Intel has explicitly reserved them for the operating system to use as it chooses for its own accounting.