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On 14/03/2007, at 3:52 PM, Caldarale, Charles R wrote:
The user space is the amount of RAM you as a process can
allocate for this single process.
No - RAM has nothing to do with the split. Process memory is the
amount
of virtual space allocated to the user; the OS may choose to use much
less RAM behind that virtual space. Page thrashing may occur, but the
process still gets to play with what it thinks is 2GB of "memory".
Arrgh! Ok - RAM was the wrong word.
This is because there needs to be some way for your process
to interact with the hardware and kernel.
The global and local descriptor tables and the page directories/tables
provide the translation between virtual space and RAM. There need not
be any split between user space and kernel space, but it's useually
more
efficient to create such a boundary.
Your kernel, and the things which are doing your process switching need
somewhere to run - if you switch them out of your 4GB of virtual address
space, how are they ever meant to 'come back to life' on the next
context
switch. As for it 'NEEDING' to be 3/1 or 2/2 - agreed - but some
amount does
need to be there. (This is all of course assuming you are running
some sort
of preemptive operating system)
Didn't the reason for choosing this size have something to do with
the memory
required by the PCI slots, etc?
Andrew
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