[TUHS] Calgary buffer modifications

[Paul Ruizendaal]

For a while I had been wondering about the origins of a modification to the V6 kernel that places the kernel buffers in a separately mapped area, freeing up space for other things. It is used in some of the early networking code, i.e. both the UoI code and the V6 BBN code (as available on the TUHS Unix Tree).

I came across the following reference in https://www.osti.gov/scitech/servlets/purl/12130675:

“One widely distributed (though undocumented) solution to this hardware limit on the model 40 was a version of Unix by Robert Sidebotham, Faculty of Environmental Design, University of Calgary. His solution was to move the I/O buffers out of kernel space.”

This would explain the modifications being bracketed with "#ifdef UCBUFMOD”.

Some questions for the old hands:

- Was this patch indeed widely known / distributed?

- Widely distributed is not the same as widely used: was it?