A Computer on Every Desk
This history of the “personal”, “home”, or “micro” computer is the history of miniaturization. When we think of the brains of a computer, we most often think of the CPU or central processing unit. This is the chip at the heart of a computer that runs your software and manages all the other hardware connected to it.
Most CPUs today are made up of billions of individual electronic switches called transistors. The ability to miniaturize these electronic switches from a light bulb sized vacuum tube to a molecule-sized transistor is what enabled computers to shrink from filling several rooms to fitting in the palm of your hand.
In November 1971, Intel released the model 4004 integrated microchip which contained 2,300 transistors as well as additional circuitry which allowed the transistors to work together. Almost every computer made before this date did not have a single integrated CPU chip, but had a CPU circuit board which contained individual transistors or small logic chips that contained just a few transistors. The Intel 4004 chip was well suited for small machines like calculators, but the birth of the personal microcomputer would have to wait until the release of the larger, more comprehensive Intel 8080 chip with 4,500 transistors in 1975.
The very first small computer designed for personal use and sold to the public was the Kenbak-1. It was created by John Blankenbaker in 1970. It was about the size of a shoebox, was made up of a variety of individual logic chips, had a total of 256 bytes of working memory and only sold 50 units.
Many people were designing and building small computers by the mid-1970s, and computer hobbyists clubs were growing in popularity. Many people saw the potential for a compact, full featured computer and began to market them commercially. With Intel’s release of the 8080 CPU in 1975, Ed Roberts and others working for MITS developed a relatively small, general purpose personal computer around it. This computer was named the Altair 8800. It was originally advertised in Popular Electronics magazine in 1974 as a kit and later as fully pre-assembled and tested units.
The Altair was designed from the beginning to be easy to use, easy to work on and expandable. The various circuitry components of the Altair were put on different cards that could be plugged into a common motherboard or back plane. The edge of each card had a 100 “pin” connector on it which is what later became the S-100 standard. Different cards could be mixed and matched to suit the needs of the owner. Most people who bought an Altair usually installed a CPU card, a memory card and a serial interface card for connecting it to an external teletype, paper tape reader, cassette tape or serial video terminal.
Electronics and computer hobbyists jumped on the chance to have an easily customizable computer of their own and the first Altair sold over 20,000 units. As is true even today, a new computer is not likely to be a success without a “killer app”. The “killer app” for the Altair was the simplified BASIC programming language which Bill Gates and Paul Allen-of a fledgling Microsoft-developed for it in 1975. Most computers of the time had to be programmed using complicated and terse machine language. While generally slower to run than a machine language program, a BASIC program could often do a similar task with just a fraction of the number of lines of code.
But What Does It Do?
Most people who grew up in the 1990’s have probably heard of the BASIC programming language. Many 8-bit home computers came with it in lieu of more expensive software packages as a way to give new computer owners something to sit down and play with right away. Despite it’s deceptive simplicity, BASIC is capable of creating full featured and useful applications. A fair amount of personal and business software sold commercially in the 1970’s and 1980’s was written in various dialects of BASIC. Some versions of BASIC could even be compiled into standalone executable programs.
If you had ordered the cheapest Altair 8800 kit when it first went on sale in 1975, you would have received a metal case, a few printed circuit boards and a large pile of electronics components. If you successfully soldered everything together and wired it up correctly, you ended up with a computer that contained just an Intel 8080 CPU, 256 bytes of storage memory and a front panel full of switches and LEDs with which to interact with the computer. The front panel allowed the operator to read and write data to each of the computer’s 256 bytes by toggling the switches to indicate the individual 1’s and 0’s to be stored. Needless to say, this was a very slow and tedious process, but with practice, programs of several hundred machine language commands could be entered and run reasonably easily. With this minimal setup there was no permanent storage and no way to view program output other than by flashing the LEDs on the panel.
If this was all an Altair was capable of, it would be just a small footnote in the history of computing. However, the modular S-100 bus and low starting price point allowed nearly anyone-not just large corporations with seven figure computing budgets-to own and experiment with a real multi-purpose computer. Within just a couple of years, dozen’s of small companies sprang up and started selling a wide variety of expansion cards and software. Some of these companies such as Cromemco and Northstar even went on to develop their own brands of personal computers to compete with the Altair.
Cromemco also developed one of the first personal computer “video cards”, the Dazzler. While it was limited to a maximum 128×128 pixel resolution and roughly 16 different colors on screen, it was a tiny fraction of the cost of a business workstation color graphics hardware. The Dazzler’s output was the same standard composite video signal we’re familiar with today and could be connected to any color TV. Each pixel on the screen could be individually controlled, which meant it’s graphics were only limited by the imagination and skill of the programmer. For comparison, the 1977 Atari 2600 game console, had a resolution of 160×192 pixels and could display 128 colors.
With the simple addition of a serial interface card, a teletype or video terminal could be connected to an Altair turning it into a computer more like what we would recognize today with a keyboard and monitor. For data storage, while paper tape and audio style cassettes were used, floppy disks quickly became the defacto standard as the price of disk drives gradually fell to a reasonable amount for the average consumer.
Once someone had a terminal and a floppy disk drive they then had everything needed to run a complete operating system like CP/M – the precurser to MS-DOS. With a computer running CP/M anyone could now run full-fledged business software such as spreadsheets, databases or word processors. Home users of course could also run larger commercial games, finance programs or a variety of home productivity software. Even CBBS, the first bulletin board software was written for and ran on and Altair!
S-100 based computers were widely used in small businesses for both clerical and manufacturing tasks. In a future article, I’ll be exploring the Dynabyte company and several of their business-oriented S-100 offerings. Due to the ease with which these machines could be upgraded to both newer CPUs and additional peripherals, some of them remained in constant use well into the 1980s.
Other than the proliferation of the Internet, the modern desktop computer is essentially a just a faster version of these early machines. In fact, an S-100 enthusiast and hobbyist community still exists today. It’s members continue to maintain vintage hardware and even design and build new S-100-compatible boards. At S-100 Computers.com you can find more information on dozens of different machines and boards.
