School of Computer Science & Engineering
University of New South Wales
Advanced Operating Systems
COMP9242 2002/S2

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The Root Pager $\sigma_0$

$\sigma_0$ is the initial address space.
$\sigma_0$ contains a mapping for each available frame of physical memory.
$\sigma_0$ is also a pager (and chief) for original servers
(tasks contained in boot image and marked as automatically run).
$\sigma_0$ maps any frame (writable) to the first task requesting it
(and ignores any further requests for the same frame).
Pages can be requested implicitly (by touching)
or explicitly (by RPC according to paging protocol).
- First job of ``OS personality'' is to request all available frames.
- Server has then control over memory.
Some special pages are used for kernel information page and memory-mapping devices.
On MIPS $\sigma_0$ runs in kernel space for no good reason.

Gernot Heiser 2002-08-07