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 - real mode

real mode:

GATE A20

Dealing with PC reverse compatibility requires defeating logic like Gate A20, which forces address rollover to a single megabyte for ancient 8086/8088 compatibility.

Microprocessor Idiosyncrasies

Sometimes you're forced to use processor features - like hardware context switching. Origionally, the earliest versions of 386BSD didn't use the hardware context switch TSS feature - but you still had to have one anyways.

Bootstrap Operation

How to bootstrap the system from hardware, loading the kernel program, itself a protected mode executable from secondary / nonvolatile / disk storage.