Porting Unix to the 386: A Practical Approach

William & Lynne Jolitz

Started open source UNIX.

Appeared in part as a 17 article magazine series in 1991-1992.

Documented the "how, what, why, who, when" of porting BSD to the 386.

Done while BSD was becoming "open source".

Porting Unix to the 386: A Practical Approach - call gate

call gate:

The Definition of the 386BSD Specification

Choosing how far to go in supporting X86 architecture in order to get a basic BSD UNIX system to be able to bootstrap the futre efforts.

System Call Interface

How to call the system's kernel from a process, using existing industry standards accross the X86 platform.

Porting Unix to the 386: The Standalone System

This article, last of the original three done altogether in 1990, on getting the critical pieces functioning independantly that we needed to do the port. Once these we obtained, the kernel was inevitable.

Processor Support -- i386.c

We initialized the processor with initial descriptor and page tables - one needs to run with the tables before activating memory/interrupt kernel functions.

System Call Handling

System calls were handled by a call gate, a 386 peculiar mechanism which allowed for ring crossing into supervisor mode using a special segment descriptor call. We simulated user mode to test prior to running in the kernel.