The Harvard Mark III, also known as ADEC (for Aiken Dahlgren Electronic Calculator) was an early computer that was partially electronic and partially electromechanical. It was built at

Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of highe ...

under the supervision of

Howard Aiken Howard Hathaway Aiken (March 8, 1900 – March 14, 1973) was an American physicist and a pioneer in computing, being the original conceptual designer behind IBM's Harvard Mark I computer. Biography Aiken studied at the University of Wisconsi ...

for the

U.S. Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage o ...

Technical overview

The Mark III processed numbers of 16 decimal digits (plus sign), each digit encoded with four bits, though using a form of encoding that is different to conventional

binary-coded decimal In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used ...

today. Numbers were read and processed serially, meaning one decimal digit at a time, but the four bits for the digit were read in parallel. The instruction length, however, was 38 bits, read in parallel. It used 5,000

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

s and 1,500 crystal

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diod ...

s. It weighed . It used magnetic

drum memory Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory. For many early computers, drum memory formed the main working memory of ...

of 4,350 words. Its addition time was 4,400

microseconds A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1000 ...

and the multiplication time was 13,200 microseconds (times include memory access time). Aiken boasted that the Mark III was the fastest electronic computer in the world. The Mark III used nine magnetic drums (one of the first computers to do so). One drum could contain 4,000 instructions and has an access time of 4,400 microseconds; thus it was a

stored-program computer A stored-program computer is a computer that stores program instructions in electronically or optically accessible memory. This contrasts with systems that stored the program instructions with plugboards or similar mechanisms. The definition ...

. The arithmetic unit could access two other drums – one contained 150 words of constants and the other contained 200 words of variables. Both of these drums also had an access time of 4,400 microseconds. This separation of data and instructions is known as the

Harvard architecture The Harvard architecture is a computer architecture with separate storage and signal pathways for instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share the same memory and pathway ...

. There were six other drums that held a total of 4,000 words of data, but the arithmetic unit couldn't access these drums directly. Data had to be transferred between these drums and the drum the arithmetic unit could access via registers implemented by electromechanical relays. This was a bottleneck in the computer and made the access time to data on these drums long – 80,000 microseconds. This was partially compensated for by the fact that twenty words could be transferred on each access. The Mark III was finished in September 1949 and delivered to the U.S. Naval Proving Ground at the U.S. Navy base at

Dahlgren, Virginia Dahlgren is an unincorporated community and census-designated place (CDP) in King George County, Virginia, United States. The population was 2,946 at the time of the 2020 census, up from 2,653 at the 2010 census, and up from 997 in 2000. History ...

in March 1950. Rebuilding the computer in its new location took the remainder of the year. It became operational in 1951, and was being operated 24 hours a day, 6 days a week by October.

References

External links

BRL report, 1955 - see ADEC
{{Mainframes 1950s computers Computer-related introductions in 1951 Electro-mechanical computers One-of-a-kind computers Vacuum tube computers Harvard University History of the United States Navy

Technical overview

See also

References

Further reading

External links