Mark-8
The Mark-8 was a microcomputer designed in 1973, based on the Intel 8008 CPU (which was the world's first 8-bit microprocessor). The microcomputer was designed by graduate student Jonathan Titus and published in the July 1974 issue of Radio-Electronics magazine as a 'loose kit' microcomputer. Today, Mark-8 is featured in the computers section of the Smithsonian.
Radio-Electronics Article
In the July 1974 issue of Radio Electronics the Mark-8 was the cover article. It offered a $5 booklet containing circuit board layouts and the Do It Yourself construction project descriptions. Titus arranged for $50 circuit board sets to be made by a New Jersey company for delivery to hobbyists. There were a couple of thousand of booklets and several hundred circuit board sets that were sold. The kit did not contain all the electronic parts which made the buyers have to gather the various parts on their own.
The Mark-8 was introduced in the Radio Electronics article as "Your Personal Minicomputer." This may be readily understood considering that the 'microcomputer revolution' had yet to happen. The word 'microcomputer' was still far from being a common term. Thus, in their announcement of their computer kit, the editors quite naturally placed the Mark-8 in the same category as the era's other minisized computers.
Mark-8 Boards
The Mark-8 consists of six boards, shown below. These 6 boards are required for the operation of the Mark-8. There is the possiblity of using up to 9 boards, 4 memory boards. (Click on the thumbnails for more information.)
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The mark-8 consisted of 6 different boards. Below are the discriptions of the boards, their tasks, and serveral images of the boards.
CPU Board
The Central Processing Unit (CPU) board contains the microprocessor IC and extra circuitry that is interfaced with the rest of the computer. The 8008 microprocessor was fabricated as an MOS circuit and the outputs only drive one low-power circuit. The outputs are buffered with an inverter before being used.
The Mark-8 computer is controlled by the 2-phase clock supplied by a crystal oscillator. This oscillator controls the pulse widths and frequency. The logical operations of the cumputer circuts are controled by the clock and synchronization signal supplied by the microprocessor. The microprocessor has 3 state-output signals S0,S1, and S2 which are used to drive the decoder. The eight possible states are then used to conrol other functions in the interface logic.
Mark-8 Additional Info
From the original article in Radio-Electronics
by Jonathan A. Titus
The Radio-Electronics Mark-8 Minicomputer is a complete minicomputer which may be used for a number of purposes, including data acquisition, data manipulation and control of experiments. It may also be used to send data to a larger computer or to a terminal such as the Radio-Electronics TV Typewriter (September 1973) ad it is essentially interfaced with a keyboard. The keyboards do not have to be ASCII encoded since the minicomputer itself can convert the input code to an equivalent ASCII code for output. This Minicomputer is not a glorified calculator and it is not intended just for educational use. It can be interfaced to a calculator (a possible future project if readers are interested) to perform complex mathematical routines, and it may also be used as a teaching tool.
Significance of Mark-8
Introduction of Mark-8 caused immediate impact in the computer hobbyists circles and spurred the formation of the Mark-8 Computer User Group, which published a newsletter. It may be interesting to see how computer-power hungry users, not only hobbyists, looked at Mark-8. Here is a letter from the National Bureau of Standards where Mark-8 was considered for application in the instrumentation for nuclear reactors (reprinted from Mark-8/Micro-8 Computer User Group Newsletter, Vol. 2, No. 4, March 28, 1976).
Mark-8 Successors
Jon with his brother, Dr. Chris Titus and David G. Larsen designed several other pieces of computer equipment. In 1976, they designed the "Dyna-Micro" computer, also featured in a Radio-Electronics cover story (Vol. 47, issues May and June 1976). It used an Intel 8080 chip and it had a small keyboard for entry of octal op codes. Three output ports provided connection pins for experiments as well as eight LEDs each. During data entry, 16 LEDs indicated an address and 8 LEDs showed the data entered into that location. So, entering a small program using the on-board Keyboard Executive (KEX) firmware was easy for students. That design was licensed to E&L Instruments, a company in Derby, Connecticut, which renamed the computer the MMD-1 or Mini-Micro Designer. The computer provided 512 bytes of EPROM (256 bytes for KEX and 256 bytes available on a user-accessible socket). It included 256 bytes of SRAM, expandable on board to 512 bytes. Eventually it also included an add-on board that increased EPROM and SRAM space, two UART serial interfaces and an audio-cassette interface for data storage.