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Early computer characteristics

Defining characteristics of some early digital computers of the 1940s (In the history of computing hardware)

Name	First operational	Numeral system	Computing mechanism	Programming	Turing complete
Zuse Z3 (Germany)	May 1941	Binaryfloating point	Electro-mechanical	Program-controlled by punched film stock (but no conditional branch)	Yes (1998)
Atanasoff–Berry Computer(US)	1942	Binary	Electronic	Not programmable—single purpose	No
Colossus Mark 1 (UK)	February 1944	Binary	Electronic	Program-controlled by patch cables and switches	No
Harvard Mark I – IBM ASCC (US)	May 1944	Decimal	Electro-mechanical	Program-controlled by 24-channel punched paper tape (but no conditional branch)	No
Colossus Mark 2 (UK)	June 1944	Binary	Electronic	Program-controlled by patch cables and switches	No
Zuse Z4 (Germany)	March 1945	Binaryfloating point	Electro-mechanical	Program-controlled by punched film stock	Yes
ENIAC (US)	July 1946	Decimal	Electronic	Program-controlled by patch cables and switches	Yes
Manchester Small-Scale Experimental Machine(Baby) (UK)	June 1948	Binary	Electronic	Stored-program in Williams cathode ray tube memory	Yes
Modified ENIAC (US)	September 1948	Decimal	Electronic	Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM	Yes
EDSAC (UK)	May 1949	Binary	Electronic	Stored-program in mercury delay line memory	Yes
Manchester Mark 1 (UK)	October 1949	Binary	Electronic	Stored-program in Williams cathode ray tube memory andmagnetic drum memory	Yes
CSIRAC (Australia)	November 1949	Binary	Electronic	Stored-program in mercury delay line memory	Yes

ENIAC

The US-built ENIAC (Electronic Numerical Integrator and Computer) was the first electronic general-purpose computer. It combined, for the first time, the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times a second, a thousand times faster than any other machine. (Colossus couldn't add). It also had modules to multiply, divide, and square root. High speed memory was limited to 20 words (about 80 bytes). Built under the direction of John Mauchly and J. Presper Eckert at the University of Pennsylvania, ENIAC's development and construction lasted from 1943 to full operation at the end of 1945. The machine was huge, weighing 30 tons, and contained over 18,000 vacuum tubes. One of the major engineering feats was to minimize tube burnout, which was a common problem at that time. The machine was in almost constant use for the next ten years.

ENIAC was unambiguously a Turing-complete device. It could compute any problem (that would fit in memory). A "program" on the ENIAC, however, was defined by the states of its patch cables and switches, a far cry from the stored program electronic machines that evolved from it. Once a program was written, it had to be mechanically set into the machine. Six women did most of the programming of ENIAC. (Improvements completed in 1948 made it possible to execute stored programs set in function table memory, which made programming less a "one-off" effort, and more systematic).

American developments

In 1937, Claude Shannon showed there is a one-to-one correspondence between the concepts of Boolean logic and certain electrical circuits, now called logic gates, which are now ubiquitous in digital computers. In his master's thesis at MIT, for the first time in history, Shannon showed that electronic relays and switches can realize the expressions of Boolean algebra. Entitled A Symbolic Analysis of Relay and Switching Circuits, Shannon's thesis essentially founded practical digital circuit design. George Stibitz completed a relay-based computer he dubbed the "Model K" at Bell Labs in November 1937. Bell Labs authorized a full research program in late 1938 with Stibitz at the helm. Their Complex Number Calculator, completed January 8, 1940, was able to calculate complex numbers. In a demonstration to the American Mathematical Society conference at Dartmouth College on September 11, 1940, Stibitz was able to send the Complex Number Calculator remote commands over telephone lines by a teletype. It was the first computing machine ever used remotely, in this case over a phone line. Some participants in the conference who witnessed the demonstration were John von Neumann, John Mauchly, and Norbert Wiener, who wrote about it in their memoirs.

Atanasoff–Berry Computer replica at 1st floor of Durham Center, Iowa State University

In 1939, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed theAtanasoff–Berry Computer (ABC), The Atanasoff-Berry Computer was the world's first electronic digital computer. The design used over 300 vacuum tubes and employed capacitors fixed in a mechanically rotating drum for memory. Though the ABC machine was not programmable, it was the first to use electronic tubes in an adder. ENIAC co-inventor John Mauchly examined the ABC in June 1941, and its influence on the design of the later ENIAC machine is a matter of contention among computer historians. The ABC was largely forgotten until it became the focus of the lawsuitHoneywell v. Sperry Rand, the ruling of which invalidated the ENIAC patent (and several others) as, among many reasons, having been anticipated by Atanasoff's work.

In 1939, development began at IBM's Endicott laboratories on the Harvard Mark I. Known officially as the Automatic Sequence Controlled Calculator, the Mark I was a general purpose electro-mechanical computer built with IBM financing and with assistance from IBM personnel, under the direction of Harvard mathematician Howard Aiken. Its design was influenced by Babbage's Analytical Engine, using decimal arithmetic and storage wheels and rotary switches in addition to electromagnetic relays. It was programmable via punched paper tape, and contained several calculation units working in parallel. Later versions contained several paper tape readers and the machine could switch between readers based on a condition. Nevertheless, the machine was not quite Turing-complete. The Mark I was moved to Harvard University and began operation in May 1944.

Colossus

During World War II, the British at Bletchley Park (40 miles north of London) achieved a number of successes at breaking encrypted German military communications. The German encryption machine, Enigma, was attacked with the help of electro-mechanical machines called bombes. The bombe, designed by Alan Turing and Gordon Welchman, after the Polish cryptographicbomba by Marian Rejewski (1938), came into productive use in 1941. They ruled out possible Enigma settings by performing chains of logical deductions implemented electrically. Most possibilities led to a contradiction, and the few remaining could be tested by hand.

The Germans also developed a series of teleprinter encryption systems, quite different from Enigma. The Lorenz SZ 40/42 machine was used for high-level Army communications, termed "Tunny" by the British. The first intercepts of Lorenz messages began in 1941. As part of an attack on Tunny, Professor Max Newman and his colleagues helped specify the Colossus. The Mk I Colossus was built between March and December 1943 by Tommy Flowers and his colleagues at the Post Office Research Station atDollis Hill in London and then shipped to Bletchley Park in January 1944.

Colossus was the world's first totally electronic programmable computing device. The Colossus used a large number of valves (vacuum tubes). It had paper-tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing-complete. Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Details of their existence, design, and use were kept secret well into the 1970s. Winston Churchill personally issued an order for their destruction into pieces no larger than a man's hand, which was to ensure the fact the British were capable of cracking Lorenz was kept secret during the oncoming cold war. Due to this secrecy, the Colossi were not included in many histories of computing. A reconstructed copy of one of the Colossus machines is now on display at Bletchley Park.

Zuse

Working in isolation in Germany, Konrad Zuse started construction in 1936 of his first Z-series calculators featuring memory and (initially limited) programmability. Zuse's purely mechanical, but already binary Z1, finished in 1938, never worked reliably due to problems with the precision of parts.

Zuse's later machine, the Z3, was finished in 1941. It was based on telephone relays and did work satisfactorily. The Z3 thus became the first functional program-controlled, all-purpose, digital computer. In many ways it was quite similar to modern machines, pioneering numerous advances, such as floating point numbers. Replacement of the hard-to-implement decimal system (used inCharles Babbage's earlier design) by the simpler binary system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time.

Programs were fed into Z3 on punched films. Conditional jumps were missing, but since the 1990s it has been proved theoretically that Z3 was still a universal computer (as always, ignoring physical storage limitations). In two 1936 patent applications, Konrad Zuse also anticipated that machine instructions could be stored in the same storage used for data—the key insight of what became known as the von Neumann architecture, first implemented in the British SSEM of 1948. Zuse also claimed to have designed the first higher-levelprogramming language, which he named Plankalkül, in 1945 (published in 1948) although it was implemented for the first time in 2000 by a team around Raúl Rojas at the Free University of Berlin—five years after Zuse died.

Zuse suffered setbacks during World War II when some of his machines were destroyed in the course of Allied bombing campaigns. Apparently his work remained largely unknown to engineers in the UK and US until much later, although at least IBM was aware of it as it financed his post-war startup company in 1946 in return for an option on Zuse's patents.