While searching for some electronic parts in a closet, I came across my first computer. After the recent discussions of first computers, programming experiences, etc. I thought some folks might enjoy seeing this.

This computer was actually built before IBM introduced the PC. Prior to the introduction of the PC, mainframe computers were the norm and there was a small market for hobbyist computers. Learning to program required access to machines, a difficult thing at the time. So it seemed logical to build my own machine. Of course, at the time that meant actually designing the computer from scratch, not just plugging boards together. I did the schematic on a roll of kindergarten paper (about 2 foot high paper); the schematic is about 15 feet long.

Every connection on every chip was hand-wired (wire-wrapped) or soldered. I built the machine into a briefcase for portability (it was a laptop!). Several interesting design notes:

Programming was in machine code, entered by hand. First the high address, then the low address, then the data, deposit the entry, then on to the next address in memory, etc. Input was in hex for convenience, output and bus data displayed in binary (it was after all, intended as a learning tool).

CPU is an Intel 8085
2K of RAM
4K of EPROM
keypad was from a calculator

For troubleshooting, you could single step through the instructions. I included circuitry to show the operation being performed (op code fetch, memory read, i/o write, etc.) as well as the bus and output data displayed in binary.

Powered it up and it still works.

Input in hex, output or inspection in binary

CPU operation display and CPU. Capacitors to reduce noise

Bottom of primary board

Kids today are so spoiled. Why, in my day, we had to ….