retro-computing

The 6th Edition Unix kernel source code has a very weird struct:

/*
 * structure to access an
 * integer in bytes
 */
struct
{
    char    lobyte;
    char    hibyte;
};

Once upon a time, I wrote a reasonably-strict-C89 C language program that “relocates” a function in memory and then runs it. That relocated function can relocate itself again, and run that copy, and so on and so forth.

Github repo for this program

I wrote a Z80 assembly program for my RC2014 Zed computer. I wanted to get a complete CP/M experience, so I used the CP/M 2.2 ASM assembler, LOAD relocator, and the DDT debugger.

I did cheat a little. Although I used the vintage RED editor for some text input, I also wrote some on my Linux laptop, and transferred to the RC2014 Zed via XMODEM.

I built a Z80-based RC2014 Zed computer from a kit.

It’s often said that DEC operating systems influenced the design of the CP/M microcomputer OS. Let’s examine that assertion by looking at how a process was laid out in memory.