I’ve written before about the fun I’ve been having building and running old hardware systems, such as a PDP-8i and a PDP-11 replica. These both use faithful scale recreations of the front panel of the machine, complete with ‘blinkenlights’ and switches. Both use the Raspberry Pi (3B+) running a program called SIMH to faithfully recreate the hardware. The PiDP-8 runs the DEC OS, while my PiDP-11 runs BSD 2.11 on top of SIMH.

Both have been much fun. The PiDP-8 I used to run some of my 80’s FORTRAN programs, while the PiDP11 ran C and a simple web server.

I also built an Altair 8800 replica called the Altairduino that gets it’s power from an Arduino board, again running simulation software to mimic the Altair. I confess I haven’t done much with this system, even though it came with an SD card full of software including CP/M.

But this winter I spent some time building two kits that really brought back my enthusiasm for the Z80, and actually has me learning and running CP/M for the first time. (I was a TRSDOS then NewDOS TRS-80 user in the ’80s).

Both kits come from ‘CPUville’, a fellow who designed, built and now sells kits for the Z80 single board computer of Byte fame. The first kit was a single board Z80 system, complete with IDE interface and true RS-232 serial port. It runs a true Zilog Z80 CPU at 1.8x MHz, which was fast ‘in the day’. It supports a second ‘display’ board that offers all the LEDs and switches to see and interact with the Z80 in real time.

The second kit starts with the Z80 single board, but then replaces the Z80 with a set of 3 8-bit CPU boards that use discrete logic chips instead of a single processor. I topped it off with it’s own display board (LEDs and switches) and it’s a fully functional 8-bit computer.

But the real fun came when I started playing with the Z80 single board and installed CP/M on an IDE->SD card ‘hard disk’. With 2+GB to play with, it’s like a world of CP/M disks all in one. I started by installing CP/M 2.2, then Microsoft FORTRAN 80, and today HiTemp’s C compiler.

There have been frustrations, such as learning to use the ED editor, and other OS programs (PIP anyone?). But the ‘proof in the pudding’ as they say has been in how well it runs my ’80s vintage FORTRAN programs. Even though it’s only an 8-bit computer, and thus suffers from a severe lack of precision – the integer is only 2 bits long – it has successfully run most of my programs. There are a couple that are simply too big for the 64K RAM, but otherwise it’s been a blast.

Today I played with compression/archive programs (to get the C compiler installed) and now it’s happily calculating the first 1000 digits of PI.

It’s slow, but what I love the most about it is that it is NOT a replica, nor a simulation – it’s a real, honest-to-goodness Zilog Z80 on a single board talking to an older laptop (with real RS-232 port in the back) via non-simulated SERIAL interface (actual 9600 baud) and I couldn’t be happier.