The Kenbak-1:

The Kenbak-1 is often called the first personal computer.  Proponents of this title explain how this is a general-purpose computer, with 256 bytes of memory, a very good and extensive instruction set, and was available to the general public, and advertised in such popular magazines such as "Scientific American".  Opponents state that the computer was not widely known, only about 40 were produced, and was not expandable in memory, or with input and output (limited to front-panel switches and lights.)  However, the title was bestowed by "The Computer History Museum" in 1986, bringing this obscure machine into history.

Obviously other contenders for that title disagree.  Since the Kenbak-1 had absolutely no provisions for interface to other input or output devices, and no reasonable possibility of expanding memory, they argue that it really wasn't a usable computer.  On the contrary, while a little awkward, the 256 byte memory allows making some fairly complex programs, as long as input and output front the front panel could be tolerated.  A program, for example, calculating a mathematical function, could have the user toggle in a multiple-digit binary-coded-decimal number, one number at a time, perform a calculation (as the instruction set and memory would support BCD math operations, and then write the output numbers one at a time on the console.  Of course, the difficulty of entering a large program would require patience. 

Overview of it's Functionality:

The Kenbak-1  is operated much like other machine-language computers of the time.  There are 8 switches on the front panel with which a 1-byte value can be entered, and stored in any of the 256 locations in memory with "store address" or "store data"  buttons.  The data in the memory can then be verified and read out on a bank of 8 lights with a "read address" or "read data" button.  Once a program in machine code is entered, the program can be executed by the "start" button, or halted by the "stop" button, or even single-stepped through one instruction at a time.  A running program can communicate with the operator by displaying any byte value on the lights, or to receive input, the program can halt, awaiting data from the operator, and the operator can the resume execution after setting the buttons.

How it was Designed:

The Kenbak-1 is a "serial" execution machine.  Rather than adding or subtracting a byte at a time in parallel fashion, arithmetic or logical operations are performed on bytes of data 1 bit at a time through a serial adder.  Most calculators at the time did this sort of arithmetic also, in a way to save transistors, but at the expense of speed.  The 256-bytes of memory were organized into two 1024-bit serial shift registers that continuously circulated the data. 

Technical Information and Documents:

There were many documents to assist a user with learning to program a Kenbak-1 and to repair and understand its circuitry.  Here are several:

• Brochures and Sales Docs:  This has a 2-page sales brochure, explaining its use and capabilities (Sept 11, 1972) a single-page request for a demonstration machine loan (January 15, 1972), a 3-page sales document aimed at education institutions explaining how a Kenbak-1 can improve computer education (January 16-18, 1973), a single page of seven customer testimonials (or "User Reactions") (January 27, 1973) and a copy of the "Scientific American" advertisement of September 1971 (total of 8 pages. 817K)
• Laboratory Exercises:  This is a 159 page workbook, which could be a stand-alone programming course.  It explains what a computer can do, on the level of assuming no knowledge of computers or even binary numbers. (2.26 MBytes.)
• Programming Reference Guide:  This 30-page manual details the fine points of programming the Kenbak-1 and the instruction set. (April 1, 1971.) (1.23MBytes)
• Theory of Operation:  This 30-page manual has 8 pages on "Installation and Maintenance" which tells how to check out the machine and test it out.  Then a Theory of Operation section has glossary of signals, block diagram, state diagram, explaination of the states, and then a full schematic of the machine.  This is essential to understanding the machine. (2.17MBytes)
• John V. Blankenbaker Biography:  An 8-page outline of a biography written by John presumably in 1986 when his machine was named the "First Personal Computer Museum".  This explains his background, early education, exposure to computers, and his motivation to make the Kenbak-1, as well as details about his early company and struggles with sales. (578 KBytes)
• Second John V. Blankenbaker Biography: a 1 page summary of John's background and work with the Kenbak, as well as further details about his career.  I believe this was written for the 2006 American Computer Museum's Stibitz award ceremony.
• Robert R. Nielsen Sr. Biography Excerpts:  This is a biography written by a man in South Carolina who worked with the Kenbak-1 in education in the early days.  While much of this is 155-page document may be beyond the interest of some computer historians, details about the Kenbak-1, the acquisition by CTI, and communications with Blankenbaker are interesting.  In this, it explains how he feels he purchased all copyrighted material INCLUDING ALL COPYRIGHTS from CTI.  He states that he feels he owned the intellectual rights to the Kenbak-1, but felt that should be released to the public domain, and anyone who wishes to reproduce a Kenbak-1 should feel free to do so.

Reproduction of Kenbak-1:

I made a reproduction of the Kenbak-1 in 2005, but didn't get it running properly until 2007 (when the state diagrams were web-published.)  <Click HERE to visit those pages>.