Harvard Unveils Mark III Calculator; Machine, New, Faster, Goes to Navy

A "memory system" capable of storing 64,000 digits and leading a computing machine through a complex mathematical problem of 4000 steps was shown at the unveiling of Harvard University's new Mark III calculating machine September 13.

Over 600 physicists, mathematicians, economists, engineers, and industrialists from all parts of the country and abroad attended the four-day Symposium on Large-Scale Digital Calculating Machines at the Computation Laboratory and observed the first public demonstration of this device. The machine will be used by the United States Navy Bureau of Ordnance.

20 Times Faster

This novel "memory system," which enables Mark III to operate 20 times faster than Mark II, completed less than two years ago, combines mechanical relay, and electronic systems.

The "memory system" consists of eight storage drums and a sequencing drum. Problems are solved by feeding information on a magnetic tape to the sequencing drum which in turn "commands" the computing section to accomplish the desired operations with the numbers in the storage drum. The results then come out of the machine on another magnetic tape.

Both the information for carrying out given operations and the numbers with which the operations are performed are represented by small magnetic spots on the surface of the rapidly rotating drums. An elaborate system of recorders and play-backs "circulate" the information between the drums and other parts of the machine.

120 RPM's

More than 4000 16-digit numbers, plus 4000 "commands" for carrying out the various operations of the machine, can be put on these nine drums. The drums revolve at speeds up to 120 revolutions per second and the magnetic spots move by the recording and play-back heads at speeds greater than 150 miles par hour.

The computing section of the machine, which carries out electronically the commands issued to it by the sequencing drum, can multiply two 16-dight numbers in a fraction over twelve thousands of a second. It can add these figures in one third of that time. Constants which are stored in the "memory system" also enable the arithmetic unit to compute automatically such functions as sine, cosine, and logarithms.

Man Outdistanced

To illustrate the machine's speed, scientists at the Computation Laboratory say that Mark III can multiply two 16 digit numbers together over 1000 times faster than a man can even write down the 32 figures to be multiplied.

Another new feature of Mark III, and one of the outstanding advances in the development of automatic-controlled computing machines, is a specially designed "coding box." The purpose of this device is to speed up the process of translating mathematical symbols and operations into a "language" the machine can use.

The "coding box" consists of a six by ton foot panel of over 200 keys, each with a number or mathematical symbol on it, Using the keyboard with its familiar symbols, a mathematician can record on a magnetic tape all the commands the machine needs to solve his problem. Essentially, he "copies" his equations on the keys of the coding machine. When fed into the machine, his commands are then transferred from the magnetic tape to the sequence drum which then controls the operations necessary to solve the problem.

Beats Mark II

By means of the "coding box," an operator can feed a problem into Mark III in a fraction of the time required by Mark II and any other calculating machines in use at the present time. Very complex problems that used to take days and weeks to "code" for the machine can now be prepared almost as quickly as an operator can punch the keys on the box.

A typical command, of which the drum will hold 4000 in sequence, might read: "select the Number in A-1 and add to it the Number in B-2 and put the sum in C-3." Such a command can be given and the work accomplished by the computing section of the machine every four thousandth of a second.

Magnetic Tape Used

As Mark III solves problems, the answers are recorded on another magnetic tape similar to the one on which the information was put into the machine. A magnetic tape is used because Mark III turns out answers faster than a typewriter can print them. To overcome this difficulty, the tape is then fed to a tape reader which relays the answers to a battery of five typewriters.

Computations of the machine are checked at several points for possible errors. During the mathematical operations in the arithmetic section of Mark III, answers are double-checked at every stage in the problem before going on to the next stage. To insure that the final typed results are correct, all numbers are recorded twice on the magnetic tape by two parallel and independent systems. Unless both numbers on the tape are identical, the striking action of the type bars sets off an alarm and stops the typewriters.

To eliminate errors that might creep into answer sheets during type-setting and printing of permanent records, the results are printed directly to pages which can be photographed and printed by offset lithography for publication by the University Press.

Built for Navy

Mark III, which was begun in May, 1946, has been built for the Bureau of the Ordnance of the U. S. Navy to be used at the Naval Proving Ground Command at Dahlgren, Virginia. It is anticipated that testing operations will have been completed by the first of the year and the machine will go to the Navy at that time.

Mark III, a bakelite and steel instrument, is about 30 feet long and fifteen feet wide and weighs close to ten tons. It contains 100 miles of wire, about 4500 vacuum tubes for the electronic operations, 3000 relays, 2500 magnetic heads and play-backs to carry the information to and from the storage drums, and 400,000 solder connections. A staff of about 40 worked on the development and construction of the machine.

Benjamin L. Moore, assistant director of the Computation Laboratory, and Way Doug Woo, assistant professor of Applied Mathematics, were directly in charge of its development, design, and construction. Mechanical design and construction of the internal high speed magnetic drum storage system, one of the major components of Mark III, was the work of Robert Wilkins, assisted by Dexter Smith.

The adder and multiplier were largely the work of Charles Coolidge. Marshall Kinkaid was mainly responsible for the over-all design of the sequencing circuits. The input and output circuits were constructed by Richard Hofheimer.

Charles Richards, who had previously worked on Mark II and will go to Dahigren with Mark III, also worked on design problems throughout the construction period.

Professor Howard Aiken, co-inventor of the original calculating machine, and Director of the Harvard Computation Laboratory had general supervision of the project.