From: David V. Winkler (dwinkler_at_windows.microsoft.com)
Date: Wed Feb 11 2004 - 14:24:48 PST
Review: Virtual Memory Management in the VAX/VMS Operating System
As suggested by the title this paper gives the inner workings of the virtual memory addressing on the VAX/VMS operating system.
The detail is very heavy on the way that individual bits are layed out in the addresses.
There are three page tables, p0, p1, and System. P0 and p1 are process specific. They appear to largely correspond to heap, and stack respectively. But since there is a level of indirection, this doesn't necessarily mean that the addresses correspond to physical memory that grows towards each other.
Of particular note is that the memory protection provided by the OS is only 4 bits of every field of every entry in the page-tables. I can't decide how I feel about this.
We see special support for null pointer dereference exceptions. Very cool.
The use of free lists for both modified and unmodified provided better cache miss performance than simple FIFO.
The article also includes a picture of Henry Levy from 1982.
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