Vacuum-tube computer
Vacuum-tube computers were initially one-of-a-kind designs, but commercial models were introduced in the 1950s and sold in volumes ranging from single digits to thousands of units.
The first departure from what was possible prior to vacuum tubes was the incorporation of large memories that could store thousands of bits of data and randomly access them at high speeds.
That, in turn, allowed the storage of machine instructions in the same memory as data—the stored program concept, a breakthrough which today is a hallmark of digital computers.
Other innovations included the use of magnetic tape to store large volumes of data in compact form (UNIVAC I) and the introduction of random access secondary storage (IBM RAMAC 305), the direct ancestor of all the hard disk drives we use today.
Even computer graphics began during the vacuum tube era with the IBM 740 CRT Data Recorder and the Whirlwind light pen.
Programming languages originated in the vacuum tube era, including some still used today such as Fortran & Lisp (IBM 704), Algol (Z22) and COBOL.
During World War II, special-purpose vacuum-tube digital computers such as Colossus were used to break German machine (teleprinter) ciphers known as Fish.
By the end of the war 10 Mark II COLOSSI were in use at Bletchley Park; they superseded the Heath Robinson.
A post-war series of lectures disclosing the design of ENIAC, and a report by John von Neumann on a foreseeable successor to ENIAC, First Draft of a Report on the EDVAC, were widely distributed and were influential in the design of post-war vacuum-tube computers.
After World War II, IBM made a version, the 603, that used vacuum tubes to perform the calculations.
[2] Surprised by market demand for it, IBM introduced in 1948 a more compact version, the 604, using 1250 miniature vacuum tubes in removable plug-in modules.
To avoid thermal cycling, heater power could be left on during standby time for the machine, with high-voltage plate supplies switched off.
Synchronous systems avoided this problem, but needed extra circuitry to distribute a clock signal, which might have several phases for each stage of the machine.
Often vacuum-tube computers made extensive use of solid-state ("crystal") diodes to perform AND and OR logic functions, and only used vacuum tubes to amplify signals between stages or to construct elements such as flip-flops, counters, and registers.
The Atanasoff–Berry computer of 1942 stored numerical values as binary numbers in a revolving mechanical drum, with a special circuit to refresh this "dynamic" memory on every revolution.
Maurice Wilkes built EDSAC in 1947, which had a mercury delay-line memory that could store 32 words of 17 bits each.
Bits in a delay line are stored as sound waves in the medium, which travel at a constant rate.
[9][10] A drum consisted of a large rapidly rotating metal cylinder coated with a ferromagnetic recording material.
Core memory offered random access and greater speed, in addition to much higher reliability.
It was quickly put to use in computers such as the MIT/IBM Whirlwind, where an initial 1,024 16-bit words of memory were installed replacing Williams tubes.
[8] The 1950s saw the evolution of the electronic computer from a research project to a commercial product, with common designs and multiple copies made,[11] thereby starting a major new industry.
The early commercial machines used vacuum tubes and a variety of memory technologies, converging on magnetic core by the end of the decade.
IBM in particular divided its computers into scientific and commercial lines, which shared electronic technology and peripherals but had completely incompatible instruction set architectures and software.
