Editing JOHNNIAC

{{short description|Early computer built by the RAND Corporation, in service 1953-1966}}
{{More footnotes needed|date=November 2015}}
[[Image:Johnniac.jpg|thumb|200px|right|Johnniac computer, Computer History Museum, California]]
The '''JOHNNIAC''' was an early computer built in 1953 by the [[RAND Corporation]] (not [[Remington Rand]], maker of the contemporaneous [[UNIVAC I]] computer) and based on the [[von Neumann architecture]] that had been pioneered on the [[IAS machine]]. It was named in honor of von Neumann, short for ''[[John von Neumann|'''John''' von Neumann]] '''N'''umerical '''I'''ntegrator and '''A'''utomatic '''C'''omputer''.<ref>{{Cite book|chapter-url=https://books.google.com/books?id=P10pDwAAQBAJ&q=JOHNNIAC+1953&pg=PA120|title=Birthing the Computer: From Drums to Cores|last=Kaisler|first=Stephen H.|date=2017-06-20|publisher=Cambridge Scholars Publishing|isbn=9781443896252|pages=120|language=en|chapter=Chapter Six JOHNNIAC}}</ref>

After being rescued from the scrap heap twice,{{clarification needed|date=February 2025}} the machine is currently at the [[Computer History Museum]] in [[Mountain View, California]].<ref>{{cite web | url=https://www.computerhistory.org/collections/search/?s=JOHNNIAC | title=Catalog Search &#124; Computer History Museum }}</ref>

Like the IAS machine, JOHNNIAC used 40-bit words, and included 1024 words of [[Selectron tube]] 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 register, named ''A'', supplied an accumulator and the machine also featured a register named ''Q'', for quotient. There was only one test condition, whether or not the high bit of the A register was set. There were no [[index register]]s, and as addresses were stored in the instructions, loops had to be implemented by modifying the instructions as the program ran. Since the machine had 12 bits of address space but only 10 bits of addressable memory, two of the address bits were unused and were sometimes used for data storage by interleaving data through the instructions.

JOHNNIAC weighed {{Convert|5000|lb|ST MT}}.<ref>{{Cite web|url=http://ed-thelen.org/comp-hist/BRL-j-n.html#JOHNNIAC|title=JOHNNIAC|last=Weik|first=Martin H.|date=December 1955|website=ed-thelen.org|series=A Survey of Domestic Electronic Digital Computing Systems}}</ref>

Numerous modifications were made to the system over its lifetime. In March 1955, 4096 words of [[magnetic-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]] secondary storage system was added as well. A [[transistor]]-based adder replaced the original tube-based adder in 1956. Numerous changes were made to the [[input/output]] peripherals as well, and in 1964, a real-time clock was added to support [[time-sharing]].

One JOHNNIAC legacy was the [[JOSS]] [[programming language]] (the '''''J'''OHNNIAC '''O'''pen '''S'''hop '''S'''ystem''), an easy-to-use language which catered to novices. JOSS was an ancestor of [[Digital Equipment Corporation|DEC]]'s [[FOCAL (programming language)|FOCAL]] and of [[MUMPS]].

The [[Cyclone (computer)|CYCLONE]] at [[Iowa State University]] was a direct clone of JOHNNIAC, and was instruction compatible with it; the [[ILLIAC I]] at the University of Illinois may have been as well. Cyclone was later updated to include hardware for [[floating-point arithmetic]].

<gallery>
File:JOHNNIAC badge.JPG|Johnniac name badge on computer frame
File:JOHNNIAC.JPG|Alternate Johnniac view
File:JOHNNIAC buttons.JPG|Johnniac keyboard
</gallery>

==See also==
* [[List of vacuum-tube computers]]

== References ==
{{Reflist}}

== External links ==
* [http://ed-thelen.org/comp-hist/johnniac.html Johnniac] entry on ''Antique Computers'' site.
* [http://www.rand.org/pubs/research_memoranda/RM5654/ The History of the JOHNNIAC] (RAND monograph)
* [http://purl.umn.edu/107692 Oral history interview with Keith W. Uncapher], [[IT History Society#Charles Babbage Institute|Charles Babbage Institute]], University of Minnesota.  Review of projects at [[RAND Corporation]] when [[Keith Uncapher]] was hired in 1950 through the early 1970s, such as JOHNNIAC, [[JOSS]], a survivable national network, and work related to the [[ARPANET]].

{{Mainframes}}

{{DEFAULTSORT:Johnniac}}
[[Category:IAS architecture computers]]
[[Category:Vacuum tube computers]]
<!-- [[Category:Early computers]]  NO!!  Category "IAS architecture computers" is already a subcat of "Early computers" -->[[Category:40-bit computers]]