Jonathan Titus

The humble Mark-8 was introduced as the “Personal Minicomputer” and is known as one of the first computers for the home. It was designed in 1972-1973 by Jonathan “Jon” Titus, a Virginia Polytechnic graduate student in chemistry and a computing hobbyist who had the desire to build his own computer. Titus already had a BS from Worcester Polytechnic, and an MS from Rensselaer Polytechnic, and his graduate work was focused on electrochemistry and the development of instrument-to-computer electronics and software.

In 1971, Titus had his first computer experience with a PDP-8 minicomputer from DEC. It was a big and expensive machine, so Jon dreamed—what if I have own computer to work with at home!? Thus the idea for Mark-8 was conceived. When Intel came out with the 8008 microprocessor in 1972, the future looked brighter. Jon procured the 8008 manuals and began conceptualizing a design. He had a computer prototype ready by the fall of 1973. As a grad student, he had no financial means to turn the Mark-8 into a commercial venture, and the idea of establishing a computer company didn’t even occur to him. Jon just wanted to share his design with other hobbyists, so he wrote a couple of letters to Popular Electronics and Radio-Electronics, two well-known hobbyist magazines, asking whether they would be interested in running a how-to-build-it article on the Mark-8. Popular Electronics turned him down, considering the Mark-8 more of an educational project than a truly useful computer, but Radio-Electronics was intrigued.

So, the Mark-8 was introduced as a ‘build it yourself’ project in Radio-Electronics’s magazine July 1974 cover article (see the article), offering a US$5 booklet containing circuit board layouts and DIY construction project descriptions, with Titus himself arranging for $50 circuit board sets to be made by the New Jersey company Techniques for delivery to hobbyists. Prospective Mark-8 builders had to gather the various electronic parts themselves from various sources. About 7500 booklets and some 400 sets of boards were eventually sold.

The Mark-8 was about the size of a large breadbox. It consisted of six circuit boards (CPU Board, Register Display, Output Ports, Memory Latch, Address Latch, and Input Multiplex), one of which held the 8008 and related chips, another the RAM chips, and so on. At the very least, it required memory of eight 256-bit RAMs (in other words, 256 bytes or words), but the memory could be expanded up to 16K by adding more RAM memory boards. There wasn’t any ROM, Jon would have had to pay Intel thousands of dollars to make ROMs for the Mark-8, which meant that every instruction (Mark-8 was programmed in assembly language only) had to be entered by the user and that the programs were lost when the machine was shut off. (RAMs retain their data only as long as the power is on.) In the basic configuration, all those programs had to be entered one bit at a time by flipping a set of toggle switches on the face of the machine—a painstaking and error-prone procedure (although there was a possibility to connect an external ASCII keyboard). The results were displayed on a panel of lights next to the switches.

Biography of Jonathan Titus

Jonathan A. Titus was born in Washington, D.C. in 1945. His father was a lawyer, who was in the Service during World War II in the intelligence branch, doing a lot of code-breaking and deciphering communications. Jon grew up in Huntington, New York, a comfortable middle-class suburb on Long Island’s north shore, where his father worked as an attorney, and his mother was a librarian. Jon has two brothers, both of them younger (Bill is three years younger and Chris is five years younger).

Jon got his start in “computers” by teaching himself about Boolean logic and numbering systems at Harborfields High School in Greenlawn, New York, when he built a 4-bit binary adder and a punched-card reader from his own design, with 24-volt relays and 6-pole switches. Then he and a friend built some relay-based “learning machines”. At this time, his dad bought a Geniac computer, which Jon used to study circuits.

After taking a B.S. in chemistry at Worcester Polytechnic Institute in 1967, Jon went on to Rensselaer Polytechnic Institute, where he picked up a master’s in 1969. Along the way, he became deeply interested in scientific instrumentation. Titus knew a great deal about electronics, he loved to tinker with gadgets in his spare time. In 1978 he got a Ph.D. in chemistry from Virginia Tech.

After Mark-8, in 1975, Jon designed the Mark-80, a computer based on the Intel 8080 microprocessor. Then he and his brother, Dr. Christopher A. Titus, 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 the entry of octal opcodes.

Jonathan Titus has been a prolific writer on various subjects related to computing. He authored and co-authored over a dozen books. Most of them cover various aspects of designs using Intel 8080 microprocessors. Others are related to microcomputer interfacing and programming. Titus also worked many years as an editor and contributor to several magazines about computers and electronics.

For his contribution to computing with Mark-8 design, Jon Titus was honored in 2002 with The George R. Stibitz Computer & Communications Pioneer Award.