Taking a break from my synth interface project and started building a microcomputer on breadboard. Why would anyone do that? To simply put, I realised I have no clue how a computer works. Considering that I want to make a living as a programmer and designer, that’s pretty embarrassing. This computer called Cosmac Elf is simple enough to build and program. Since there’s no operating system, programs have to be entered in assembly language. In other words, I have to enter the program flipping switches that represent zeros and ones.
Some historical context: back in the 1960’s integrated circuits (IC, chip or microchip) became widespread in the military and space industry. These devices allowed replacing otherwise large, expensive hand-assembled circuits with single chips. The integrated circuit can be thought of as a miniature circuit in silicon wafers. They were first used where light and small computers were necessary, in nuclear missiles and the Apollo space vehicles. ICs also allowed smarter, smaller and cheaper instruments for navigation, communication, recon or weapon control in jet fighters. Since the military and the aerospace industry desperately needed millions of microchips, the US government aggressively supported IC manufacturing. By the 1970’s IC prices plummeted and manufacturers managed to squeeze thousands of components on a single chip, rather than a few dozen or hundred a decade earlier. Intel successfully introduces the first microprocessor, a programable CPU on a single chip. The Intel 4004 made building a computer simpler and cheaper. In the beginning microprocessors were expensive. By the mid seventies prices fell from hundreds of dollars to 30-50 dollars. Suddenly computers were within the reach of students, teenagers and hobbyists.
- Intel 4004, the world’s first microprocessor
In 1976 and 1977 the ‘Popular Science’ magazine publishes a series of articles on how to build a microcomputer for about $80. A computer so cheap and simple that anyone can build! The heart of the computer called ‘Cosmac Elf’ was the RCA1802 COSMAC (Complementary Symmetry Monolithic Array Computer) microprocessor. It was a very simple animal: tiny memory, no hard drive to backup programs that had to be entered in binary, no operation system, no keyboard. Just switches and lights. Yet it was expandable and the article even explained how to add a video IC so that the Cosmac Elf could create graphics or text and display them on a TV screen. Users could also build an interface to be able to save and load programs using casette player.
The Cosmac Elf became the first computer for many. Those who learnt programming with the Cosmac Elf became the generation who programmed computer games in the 80’s and built the Internet and the World Wide Web in the 90’s. However simple is the Cosmac Elf, it has a structure and architecture of a modern computer. If you learnt to program the Cosmac Elf, you could program anything.
Shepherding bits and bytes 