The JOHNNIAC was an early computer built by RAND

RAND

RAND Corporation is a nonprofit global policy think tank first formed to offer research and analysis to the United States armed forces by Douglas Aircraft Company. It is currently financed by the U.S. government and private endowment, corporations including the healthcare industry, universities...

 that was based on the von Neumann architecture

Von Neumann architecture

The term Von Neumann architecture, aka the Von Neumann model, derives from a computer architecture proposal by the mathematician and early computer scientist John von Neumann and others, dated June 30, 1945, entitled First Draft of a Report on the EDVAC...

 that had been pioneered on the IAS machine

IAS machine

The IAS machine was the first electronic computer built by the Institute for Advanced Study , in Princeton, New Jersey, USA. It is sometimes called the von Neuman machine, since the paper describing its design was edited by John von Neumann, a mathematics professor at both Princeton University...

. It was named in honor of von Neumann, short for John v. Neumann Numerical Integrator and Automatic Computer. JOHNNIAC is arguably the longest-lived early computer, being used almost continuously from 1953 for over 13 years before finally being shut down on February 11, 1966, logging over 50,000 operational hours.

After two "rescues" from the scrap heap, the machine currently resides at the Computer History Museum

Computer History Museum

The Computer History Museum is a museum established in 1996 in Mountain View, California, USA. The Museum is dedicated to preserving and presenting the stories and artifacts of the information age, and exploring the computing revolution and its impact on our lives.-History:The museum's origins...

 in Mountain View, California.

Like the IAS machine, JOHNNIAC used 40-bit words, and included 1024 words of Selectron tube

Selectron tube

The Selectron was an early form of digital computer memory developed by Jan A. Rajchman and his group at the Radio Corporation of America under the direction of Vladimir Zworykin, of television technology fame...

 main memory, each holding 256 bits of data. Two instructions were stored in every word in 20-bit subwords consisting of an 8-bit instruction and a 12-bit address, the instructions being operated in series with the left subword running first. The initial machine had 83 instructions. A single A register supplied an accumulator, and the machine also featured a Q, for quotient, register as well. There was only one test condition, whether or not the high bit of the A register was set. There were no index registers, and as addresses were stored in the instructions, loops had to be implemented by modifying the instructions as the program ran. Since the machine only had 10 bits of address space, two of the address bits were unused and were sometimes used for data storage by interleaving data through the instructions.

Numerous modifications were made to the system over its lifetime. In March 1955 4096 words of core memory were added to the system, replacing the earlier Selectrons. This required all 12 bits of addressing, and caused programs that stored data in the "spare bits" to fail. Later in 1955 a 12k-word drum memory

Drum memory

Drum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....

 secondary storage system was added as well. A transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

-based adder replaced the original tube-based one in 1956. Numerous changes were made to the input/output

Input/output

In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...

 peripherals as well, and in 1964 a real time clock was added to support time sharing.

One JOHNNIAC legacy was the JOSS

JOSS

JOSS was one of the very first interactive, time sharing programming languages.JOSS I, developed by J. Clifford Shaw at RAND was first implemented, in beta form, on the JOHNNIAC computer in May 1963...

 programming language

Programming language

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

 (the JOHNNIAC Open Shop System), an easy-to-use language which catered to novices. JOSS was an ancestor of DEC

Digital Equipment Corporation

Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

's FOCAL

FOCAL programming language

FOCAL, , is an interpreted programming language resembling JOSS.Largely the creation of Richard Merrill, FOCAL was initially written for and had its largest impact on the Digital Equipment Corporation's PDP-8 computers. Merrill wrote the original and classic FOCAL-69 interpreters for the PDP-8...

 and of MUMPS

MUMPS

MUMPS , or alternatively M, is a programming language created in the late 1960s, originally for use in the healthcare industry. It was designed for the production of multi-user database-driven applications...

.

The Cyclone at Iowa State University

Iowa State University

Iowa State University of Science and Technology, more commonly known as Iowa State University , is a public land-grant and space-grant research university located in Ames, Iowa, United States. Iowa State has produced astronauts, scientists, and Nobel and Pulitzer Prize winners, along with a host of...

 was a direct clone of JOHNNIAC, and was instruction compatible with it (the ILLIAC I

ILLIAC I

The ILLIAC I , a pioneering computer built in 1952 by the University of Illinois, was the first computer built and owned entirely by a US educational institution, Manchester University UK having built Manchester Mark 1 in 1948.ILLIAC I was based on the Institute for Advanced Study Von Neumann...

may have been as well). Cyclone was later updated to include a hardware floating point system.