The LINC: An Early "Personal Computer"

In 1962, a cat living at the National Institute of Mental Health in Bethesda, Maryland named Jasper became the first cat—indeed the first animal of any kind—to have his average neuroelectric responses ("brain waves") recorded and analyzed by digital computer. That computer was the LINC, a 12-bit minicomputer with four modular user interface subsystems. LINC focused on direct user access, challenging the then-dominant paradigm of computing as a series of batch-style jobs.

LINC was the brainchild of MIT physicist Wes Clark. Prior to working on LINC, Professor Clark worked on two of computer history's most important early transistor computers, the TX-0 (1956) and TX-2 (1959). Clark worked on the TX-0 with Ken Olsen, who went on to found Digital Equipment Corporation (DEC). In 1961, LINC began as collaboration with several MIT research agencies—the Lincoln Lab, the Communications Biophysics Lab (CBL), and the MIT Digital Computer Lab. Clark was attending lectures given by Professor Walter Rosenblith, a neuroscientist and head of CBL. Rosenblith was encouraging students and researchers to make use of some of DCL's new computers—the TX-0 and TX-2. One of Rosenblith's grad students, Charles Molnar, fostered liaisons between the computer folk and the "wet" scientists and later was crucial to the product trajectory of LINC.

At that time, the enormous development of the SAGE air defense system monopolized time on the TX-0 and TX-2 machines. Clark met with two CBL members about building a specific digital device suited to their purposes (recording brain waves) and began designing LINC in May 1961. Within several months, a working prototype (including a simple but versatile magnetic tape system) was demonstrated at the National Academy of Sciences. Soon after, Clark demonstrated the LINC at the National Institute of Mental Health where, you guessed it, Jasper was living.

From this humble beginning, a federally funded research program to evaluate digital computers in the laboratory was established—with Rosenblith as the prime mover. A separate group was founded to invite a dozen or so scientists from around the country to learn not only to use LINC in the labs, but to maintain it as well. LINCs were prepared as kits, and in the summer of 1963 the first group of scientists arrived "some with golf clubs they would never use," wrote Clark. As the LINCs were completed, the scientists involved had to write and demonstrate a program that related to their own work.

LINC came with a novel user interface: a variable-persistence phosphor CRT to allow photographic (Polaroid) recording of electrical signals, A/D and D/A converters, and the famous "LINC Tape," a reel of magnetic tape that fit in a shirt pocket and was capable of recording relatively large amounts of experimental data.

A second group of scientists went through the program right after the first, deploying their new equipment to great success in their own laboratories, and by the next summer, in 1964, the impressive list of LINC-driven research included:

• Operant conditioning of pigeons and monkeys.
• Measurement and analysis of evoked potentials in thalamic and cortical neurons.
• Pulsatile blood flow, cardiac muscle behavior, hydrodynamics of the mammalian arterial system.
• Interfacing to mass spectrometers for genetics research.

LINC went on to be produced by DEC (about 50 were made) and was also produced in a variant, the LINC-8, which Clark designed with Dick Clayton. (In fact, LINCs were made up of DEC modules—"black boxed" circuit modules allowing quick prototyping and development.) In all, some 1200 LINC or LINC variants (such as the PDP-12) were in use internationally. One of LINC's most interesting contributions is the LINC Tape drive—this became the basis for DEC Tape, a format used in hundreds of thousands of machines worldwide.

The achievements embodied in LINC are impressive by themselves, but just as interesting and profound is the underlying assumption of a computer as something the user should interact with directly. The LINC interface was in sharp contrast to the predominant interface of the day—batch-style jobs submitted on punch cards to a mainframe system operator.

Another MIT (and TX-0) alumnus, Gordon Bell, noted that the people who worked on computer development at MIT at that time signed up for computer time (rather than submitting batch jobs). Grad students had complete, unfettered access to the machine's hardware, something almost unthinkable in a campus-computing environment. Not coincidentally, Bell, Olsen, and others formed the nucleus of the minicomputer industry itself—by building machines at DEC that embodied direct user access and interactivity as a more effective computing environment than timesharing.

Only a year after the experiment, DEC introduced the PDP-8, one of the most successful minicomputers of all time and an example of this "power to the people" philosophy of direct user interaction. Thanks, Jasper!

For Further Reading

Clark, W., "The LINC Was Early and Small," in Goldberg, A, (ed), A History of Personal Workstations, New York: ACM Press, 1988.

Programming the LINC, 1965, TCMHC #102626150

Clark, W: LINC drawings "L-1 - the world's simplest computer" drawings .iDigital Equipment Corp:.LINC-8, TCMHC #102626151

Clark, W., Computer Museum Lecture, November 18, 1981. VHS video, TCMHC # 102626152

(TCMHC numbers refer to documents from The Computer Museum History Center's permanent archive).