The Harvard Mark I, 1943

It should be said that Aiken mistrusted the concept of storing program within a computer. The Mark I was programmed to solve problems by means of a paper tape on which coded instructions were punched. Once so programmed, the calculator could be easily operated by persons with little training. For input and output, it used three paper tape readers, two card readers, a cardpunch, and two typewriters. The Mark I was used for military purposes, including the development of the atomic bomb.

Aiken was not familiar with the Analytical Engine when he designed the Mark I. Later, after people had pointed out Babbage's work to him, he was amazed to learn how many of his ideas Babbage had anticipated.

The main difference between the Analytical Engine and The Mark I is that the latter¹ was operated by electricity instead of steam. Electricity was also used to transmit information from one part of the machine to another, replacing the complex mechanical parts by relays and electromagnetic components.

But, along with² several other electromechanical computers built at about the same time, the Mark I was scarcely completed before it was obsolete. The electromechanical machines simply were not fast enough. Their speed was seriously limited by the time required for mechanical parts to move from one position to another. For example, the Mark I took six seconds for a multiplication and twelve for a division; this was only five or six times faster than what a human with an old desk calculator could do.

Continuing his work, Aiken completed the improved versions of the Mark I (Mark II, III and IV). He also wrote numerous articles on electronics, switching theory³, and data processing as well as developed the first computer science program⁴ at Harvard University. On the other hand, Aiken advised the National Bureau of Standards⁵ not to support the development of computers. He was sure that there would never be a need for more than five or six computers nationwide.

Notes: ¹ the latter – последний (из двух названных, из упомянутых);

²along with – наряду с;

³switching theory – теория переключательных (релейных) схем;

⁴computer science program – программа по теории вычислительных машин и систем;

⁵the National Bureau of Standards – Национальный институт стандартов и технологий (U.S.).

Part II (COLOSSUS, ENIAC, EDVAC)

What was needed was a machine whose computing, control and memory elements were completely electrical. In this case, the speed of operation would be limited not by the speed of mechanical moving parts but by the much greater speed of moving electrons.

World War II gave impetus¹ and funding to computer research. The military needed faster machines for ballistic calculations and for breaking the German secret codes.

One of the earliest electronic digital computers was called the Colossus. The machine was developed by a team led by the British engineer Tommy Flowers in 1943. Its existence was kept so secret that it was not revealed until decades after it was built. British cryptographers used this machine to crack ciphers and codes produced by the German electromechanical devices called the Enigma and the Geheimschreiber (“Secret Writer”). The machine used approximately 1800 vacuum tubes for computations. Larger and more sophisticated versions were built over the next two years.

The first general-purpose all-electronic computer was ENIAC(an acronym for E lectronic N umerical I ntegrator a nd C omputer). (See Figure 2)Designed by two American engineers, John Mauchly and Presper Eckert, ENIAC was put into operation at the University of Pennsylvania in 1946.

Figure 2

ENIAC

First introduced in 1946, ENIAC remained in service until 1955. A portion of the machine is now on exhibit at the Smithsonian Institution in Washington, D.C.

The 30-ton machine was 5.5 meters high and 24 meters long. It contained 18,000 vacuum tubes linked by 800 kilometers of wiring, 70,000 resistors, 10,000 capacitors, 6,000 switches and 1,500 relays. Approximately 2,000 of the computer’s vacuum tubes were replaced each month by a team of six technicians. It was the most complex electronic system developed up to that time. ENIAC was 500 times as fast as the best electromechanical computer. A problem that took one minute to solve on ENIAC required eight to ten hours on an electromechanical machine. It performed about 5,000 additions per second. Many of ENIAC’s first tasks were for military purposes, such as calculating ballistic tables and designing atomic weapons.

As ENIAC was not a stored program machine, it had to be reprogrammed for each task, a process that could take several days. The next computers were built so that programs could be stored in internal memory and could be easily changed to adapt the computer to different tasks.

EDVAC (an acronym for E lectronic D iscrete V ariable A utomatic C omputer) was constructed at about the same time as ENIAC. But EDVAC was the more advanced of the two machines. Two innovations that first appeared in EDVAC have been used in every computer since. First, EDVAC used binary notation to represent numbers inside the machine. Binary notation is a system for writing numbers that uses only two digits (0 and 1), instead of the ten digits (0-9) used in the conventional decimal notation. Binary notation is now recognized as the simplest way of representing numbers in an electronic machine. Second, EDVAC's program was stored in the machine's memory, just like the data. Previous computers had stored the program externally on punched cards or punched tapes. A stored-program computer is usually called a von Neumann machine in honor of the originator of the stored-program concept.

Notes: ¹to give impetus to – дать стимул к.