THREE INITIAL PC UTILITIES:

The second article in the "PORTING UNIX TO THE 386" series discussed the utilities we had to build to test the port on an actual 80386 PC.
By far, the most popular article.

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

Its not enough just to load the kernel and go, you need to insure its the kernel bit-for-bit by the time you run it.

Requirements for a DOS PC Utility to boot a 386BSD UNIX kernel.

Our kernel is a UNIX executable file, just like all of its applications. So what does the a.out file, compiled and loaded usiing GCC and utilities look like?

Why we wrote PC utilities to port UNIX with - the advantage of working from a primitive OS that runs on the absolute machine.

DOS C program for loading 386BSD kernel from DOS, and executing it, taking over the machine.

After loading the kernel program, we enter protected mode to start up the 386BSD kernel, itself a protected mode program like its own applications.

First thing the kernel does is open its root filesystem - so we need a way to write a filesystem onto the hard disk, adjacent to the DOS filesystem, which is what this utility does.

Once the system is debugged and tested, the next step was to load on more code to expand with. So we moved "tar balls" to the swap space with this utility to provide a primative file upload capability.

Ironically, these utilities advanced progress fast enough that once the kernel was operational, the biggest obstacle became booting off of DOS. So the next step was to implement a bootstrap and standalone system so that we could rid ourself of DOS entirely.

Synopsis of what 386BSD was intended to be in the 1989-1990 timeframe.

What should have happened was that Berkeley should have released a basic 386 system binary and source release, and followed it up with a general release.

The tool chest for 386BSD cross support included compiler, assembler, loader, libraries and include files. It did not include an emulation environment.

Understanding the boundary between research and development with BSD, and where a balance between commercial efforts can be struck.