Harvard Mark I

 

The IBM Automatic Sequence Controlled Calculator (ASCC), called the Mark I by Harvard University, was an electro-mechanical computer.

The electromechanical ASCC was devised by Howard H. Aiken, built at IBM and shipped to Harvard in February 1944. It began computations for the U.S. Navy Bureau of Ships in May and was officially presented to the university on August 7, 1944. It was very reliable, much more so than early electronic computers. It has been described as "the beginning of the era of the modern computer" and "the real dawn of the computer age".

Design and construction

The building elements of the ASCC were switches, relays, rotating shafts, and clutches. It was built using 765,000 components and hundreds of miles of wire, comprising a volume of 51 feet (16 m) in length, eight feet (2.4 m) in height, and two feet (~61 cm) deep. It had a weight of about 10,000 pounds (4500 kg). The basic calculating units had to be synchronized mechanically, so they were run by a 50-foot (~15.5 m) shaft driven by a five-horsepower (4 kW) electric motor. From the IBM Archives:

The Automatic Sequence Controlled Calculator (Harvard Mark I) was the first operating machine that could execute long computations automatically. A project conceived by Harvard University's Dr. Howard Aiken, the Mark I was built by IBM engineers in Endicott, N.Y. A steel frame 51 feet (16 m) long and eight feet high held the calculator, which consisted of an interlocking panel of small gears, counters, switches and control circuits, all only a few inches in depth. The ASCC used 500 miles (800 km) of wire with three million connections, 3,500 multipole relays with 35,000 contacts, 2,225 counters, 1,464 tenpole switches and tiers of 72 adding machines, each with 23 significant numbers. It was the industry's largest electromechanical calculator.

The enclosure for the Mark I was designed by futuristic American industrial designer Norman Bel Geddes. Aiken considered the elaborate case to be a waste of resources, since computing power was in high demand during the war and the funds ($50,000 or more according to Grace Hopper) could have been used to build additional computer equipment.

Operation

The Mark I had 60 sets of 24 switches for manual data entry and could store 72 numbers, each 23 decimal digits long.It could do three additions or subtractions in a second. A multiplication took six seconds, a division took 15.3 seconds, and a logarithm or a trigonometric function took over one minute.
The Mark I read its instructions from a 24 channel punched paper tape and executed the current instruction and then read in the next one. It had no conditional branch instruction. This meant that complex programs had to be physically long. A loop was accomplished by joining the end of the paper tape containing the program back to the beginning of the tape (literally creating a loop). This separation of data and instructions is known as the Harvard architecture (although the exact nature of this separation that makes a machine Harvard, rather than Von Neumann, has been obscured with the passage of time, see Modified Harvard architecture). The first programmers of the Mark I were computing pioneers Richard Milton Block, Robert Campbell, and Grace Hopper. 

Sumber: Wikipedia.