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

[Alexander Kapshuk <alexander.kapshuk@gmail.com>]

On 10/09/2013 05:17 AM, gottlieb@nyu.edu wrote:
> 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
>
Thanks a lot for the explanation. Much appreciated.