Re: [gentoo-user] re: NX (Execute Disable) protection cannot be enabled: non-PAE kernel! [dmesg]

[gottlieb@nyu.edu]

On Tue, Oct 08 2013, Alan McKinnon wrote:

> That is correct, with 3G physica RAM, you will not benefit from using
> PAE at all. I don't think it interferes with anything if you do have it,
> I recall a time when RedHat shipped 32 bit kernels that were PAE-enabled.
>
> Briefly, the way it works is that the kernel assigns blocks of memory to
> different processes. So a single process can still only access 4G of
> memory, but two different process don't anymore have to address the same
> 4G of memory like you must do without PAE. But you still don't get to
> give your 32 bit database more than 4g of RAM

Agreed.  Virtual addresses refer to those in the program (really
process).  Physical addresses address refer to those in the hardware
(i.e. addresses in the RAM itself).  To have a single process able to
access extra memory would be to increase the *virtual* address range.
PAE (*physical* address extension) enables more RAM to be accessed (by
the hardware not by a single process), but does not increase the virtual
address range.

When pdp-11s added I and D space, that increased the virtual address
range by a factor of two.  The I/D bit (instruction/data) was
essentially an extra bit of virtual address.

allan