I am going to take you on a brief journey back through time to an era where you had to roll your own computer if you wanted one. I built my first computer from scratch back in 1978 while I was a junior at the US Air Force Academy. Here's a list of it's 'features':
Chassis: S-100 backplane cabinet with power supply
CPU: Intel 8085 8-bit 3 MHz clock, 64 kB address space (16-bit)
Ram: 32kB + 2kB (cpu card) + 1kB (video card)
Display: RCA 12” B&W TV - 64 characters x 16 lines ASCII text
Video: Processor Technology VDM-1 memory mapped video card
Storage (initial): Tarbel Tape Controller + cassette tape player (using the remote microphone and headphone jacks for I/O)
Storage: 8” 256 kB single sided / single density floppy (added later)
I learned my electronics helping my dad fix TVs in the garage at home. I would test tubes, help align the picture tube, and if need be, pull the picture tube out of the set and put the new one back in (my dad was in a wheelchair thanks to an ambush during the Korean war). He taught me how to read a schematic before I was in high school. That helped me get my first job while I was high school -working in an electronic parts store getting parts from the shelves for customers. You can learn a lot just asking them about their project :)
In the picture of my desk below you can see the 'monitor' and keyboard in the yellow square and the blue computer on the lower shelf in the red square. This was taken in 1979. I think I was the only person at the school at the time that had a computer on their desk. To work on a computer (a mainframe for most people) you had to go the computer science department in Fairchild Hall (the academic building) or to a terminal room in the dorm (just one in each dorm building!). Note the lack of any kind of network connectivity - that simply didn’t exist at that time (as we understand it today).
My dorm room desk. [my photo]
How it was built
A friend from high school hand-drew the CPU card schematics at his kitchen table over the course of two nights while I was home on leave (I wish I had those today!). Then we went to a parts store and bought a bag-o-parts. When I got back to school, I ordered the cabinet which included a power supply and an S-100 backplane similar to the one shown in the picture below. Each slot would hold one card. Each card was about 5” x 10”. My machine (eventually) had these cards:
- CPU card (with boot ROM, 2k of 'scratchpad' memory [2114's] and the keyboard port). This card was wire-wrapped (Each chip was in a socket and each socket had long square posts. A thin wire was twisted on one pin post to another pin post - a point to point connection for each pin on the board! Only power pins were soldered)
- VDM-1 video card (made from a kit). I took the video output and injected it into the video pre-amp in the TV to bypass the RF converter and audio filter to get the best display.
- Two 8 kB memory cards. The 2102 memory chips were stacked two high to make each card 16 kB for a total of 32 kB.
- Tarbel tape controller (also a kit)
- Tarbel disk controller (yet another kit). The drive was a bare drive and I made my own power supply for it.
An S-100 backplane (By Cromemco - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=27000270)
After I finished wire-wrapping the CPU card, I mailed to my friend who checked it out in his IMSAI 8080 (like the picture below. My computer did not have the front panel lights and switches like shown here). Yep, he was a first-class geek (did I mention he was self-taught?). He fixed some errors I made and added a couple of signals he forgot, added a 8 kB UV- EPROM that contained the boot routine, a line editor and an 8080 macro assembler (Yes - in one 8k ROM!). Then he mailed it back. By then I was working on assembling my other cards. The most amazing part was that it actually worked when I was done putting it all together!
So what could I do with it? Not a whole lot. I learned to code in 8080 assembly language, later had the FORTH programming language on it, as well as 24k Basic (just not at the same time!). But what I LEARNED from it was tremendous! Building a system piece by piece really teaches you what each chip and signal does.
Today you can go online, order a Raspberry Pi Zero for a fraction of what a single bare S-100 card cost me back then and have an order of magnitude (or more!) more capability in your shirt pocket than my desktop machine could even conceive of!
Where do you think will technology be 40 years from now?
I have other topics I plan to write about (as time permits!):
My Calculator Collect
... and who knows what else might inspire me! Stay tuned....