First Computer

This machine was built to learn about computers and because I met a guy who told me with the up most assurance that a computer would never be built by a single person - it was simply to complex.  At the time I was working at Link Singer building the first digital computer for a Link trainer.  That computer was huge, it filled several racks of equipment, and was one of the very first built using integrated circuits.  I remember that a dual flip-flop from Motorola cost $9.00 and had to have a support chip for every 5 or six of them.  That machine itself was very interesting - but that's another story.

I decided to build this machine (it never had a name) to see if it could be done.  I started in 1971 and finished in 1976

All the hardware was scrounged from surplus yards or built from scratch.  The chips were bought from a guy that made a living from picking up discarded chips from Intel, Motorola, and Fairchild, testing them and reselling them. He also kited and sold one of the first computers concurrent with the IMSI.

From the top of the rack down was:

• Dual audio tape recorders (I never got them running for digital).
• Paper tape reader.  I built the case for it from a aluminum chassis.
• Control panel.  At the time all computers had a control panel - none do now.  With the control panel I could enter the boot routine, inspect individual memory cells and make changes as necessary.
• Below the shelf was a paper tape punch and below that a power supply control consol. 
• The teletype is a surplus military that ran at a blazing 110 baud.
• behind the rack is my Heathkit ham radio with a kilowatt amplifier right behind the teletype.

If you look closely at the table in the foreground holding the TTY you will see a copy of the first Byte magazine.  I still have a complete set of the first year of Byte which makes for very interesting reading on a rainy day.

When I finally got this beast running I used it contact a second computer in downtown San Diego over a 300 baud modem (not shown).  That machine had an assembler, written in Basic, for my machine.  That way I could create a program on the distant machine, assemble it and download the result to run on my machine.

The first piece of software I wrote was a relocating linking loader for my machine.  With that I could fill up my 2K words of memory with what ever I needed.

First Computer Inside

This is a shot of the inside of the machine showing some of the circuit cards I built and my trusty 'scope to keep it all running.  Each card was built using 30 gage wire wrap wire.  The card on the extender was a serial controller for the teletype.  It had one of the first UARTs for the actual bit banging.  The large white ribbon cables were used to interconnect the cards on the front side.  On the back plane side they were wire wrapped using 26 gauge wire.

The card on the left side, showing five integrated circuits, is the CPU.  This card is the part of the compute still in existence and is shown below.

CPU Card

The CPU card was built using SN74181 chips from Texas Instruments.  This card has four of them in the middle of the board with support TTL around them.  On the right side was a set of registers (16 of them) used to hold intermediate results from the '181s as they did there work.  The chips on the left side were the bus buffers.  The chips between the '181's were the high speed look ahead carry logic.

This machine ran at a blazing 1 mHz clock rate but could do all the things that any modern machine could do (plus some that they don't).  Each instruction was 16 bits wide and there were a total of 45 instructions.  Each instruction could be either indexed or indirect or both.  The instruction set was copied from a commercial mini-computer that I was using at work (Philco/Ford at the time).

Memory for this machine was built from 1 K bit dynamic RAM and at the end I had four cards with 1K X 8 on each card or a total of 2 K of 16 bit memory.  Since the chips were dynamic I had a refresh clock running at all times.  Without that they would forget what they were programmed with.

Booting this machine was a chore.  I had to toggle in each of the 20 or so instructions through the front panel each time I started up.  This boot strap program would load what ever program was in the paper tape reader.  That was the BBS software or the assembler or the loader or what ever I was working on at the time.  

I was able to get the machine to control my ham rig and send Radio Teletype signals (RTTY) using it.  I was also able to build one of the very first bulletin board systems (BBS) in San Diego where the user would call into my home phone and the modem would answer and give the remote user complete control of my computer.  I think this is the first time I started using the name Zeke for a computer.  The BBS was named Zeke and was well known in this area.  It used to tie up my home telephone for hours at a time.  This was long before AOL was a dream in anyone's eye.

After I got the whole thing running and was able to link and load the first assembled program for the computer I broke out the wire cutters and cut the whole thing to pieces.  It had served its purpose and besides I had a new toy to play with - Zeke was a Z80 machine that I built the first SETI search system on.