Four-Phase Systems

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Four-Phase Systems, Inc.
FounderLee Boysel
Defunct1981 (1981)
FateAcquired by Motorola
HeadquartersCupertino, CA, USA
ProductsSemiconductor main memory, LSI MOS logic, central processing unit, microprocessor

Four-Phase Systems, Inc., was a computer company, founded by Lee Boysel and others, which built one of the earliest computers using semiconductor main memory and MOS LSI logic. The company was incorporated in February 1969 and had moderate commercial success. It was acquired by Motorola in 1981.[1]


A Four-Phase IV/90 computer

The idea behind Four-Phase Systems began when Boysel was designing MOS components at Fairchild Semiconductor in 1967. Boysel wrote a manifesto explaining how a computer could be built from a small number of MOS chips. Fairchild made Boysel head of a MOS design group, which he used to design parts satisfying the requirements of his putative computer. After doing this, Boysel left to start Four-Phase in October 1968, initially with two other engineers from his Fairchild group as well as others. Boysel was not sued by Fairchild, perhaps because of chaos caused by a change in Fairchild management at that time.[2] When the company was incorporated in February 1969, he was joined by other engineers from the Fairchild group. Robert Noyce, co-founder of Intel, was an early board member.[3]

Boysel arranged for chips to be fabricated by Cartesian, a wafer-processing company founded by another engineer from Fairchild.[4] Four-Phase showed its system at the Fall Joint Computer Conference in 1970. By June 1971, Four-Phase IV/70 computers were in use at four different customers, and by March 1973, they had shipped 347 systems to 131 customers.[5] The company enjoyed a substantial level of success, having revenues of $178 million by 1979.

In 1982, Four-Phase was sold to Motorola for a $253 million stock exchange (equivalent to $799 million today).[6] The former location of the business on N De Anza Blvd is now Apple's Infinite Loop campus.


The Four-Phase CPU used a 24-bit word size. It fit on a single card and was composed of three AL1 chips, three read-only-memory (ROM) chips, and three random logic chips. A memory card used Four-Phase's 1K RAM chips.[7] The system also included a built-in video controller which could drive up to 32 terminals from a character buffer in main memory.[8]

The AL1 is an 8-bit bit slice which contains eight registers and an arithmetic logic unit (ALU). It was implemented using four-phase logic and used over a thousand gates, with an area of 130 by 120 mils (3.3 mm by 3 mm). The chip was described in an April 1970 article in Computer Design magazine.[9][10] Although the AL1 was not called a microprocessor, or used as one at the time, it was later dubbed one in connection with litigation in the 1990s, when Texas Instruments claimed to have patented the microprocessor. In response, Lee Boysel assembled a system in which a single 8-bit AL1 was used as part of a courtroom demonstration computer system, together with ROM, RAM and an input-output device.[11][12] The AL1 is arguably the first microprocessor used in a commercial product (vs the Intel 4004, the first commercially available microprocessor).[13][14]


  1. ^ Bassett, Ross Knox (2007). "Ch. 5: It Takes an Industry". To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology. JHU Press. pp. 256, 267, 262. ISBN 978-0-8018-8639-3.
  2. ^ Bassett 2000, pp. 119–120, 132
    Bassett, Ross (2000). "When is a Microprocessor not a Microprocessor? The Industrial Construction of Semiconductor Innovation". In Finn, Bernard S.; Bud, Robert; Trischler, Helmuth (eds.). Exposing Electronics. Science Museum. pp. 115–134. ISBN 978-1-900747-48-6.
  3. ^ "Lee Boysel – Making Your First Million And Other Tips for Aspiring Entrepreneurs".
  4. ^ Bassett 2000, pp. 120–1
  5. ^ Bassett 2007, pp. 257–8
  6. ^ Bassett 2000, p. 130
  7. ^ Bassett 2000, pp. 122, 124
  8. ^ Brochure, System IV/70, Four Phase Systems. From the Computer History Museum. Accessed on line June 11, 2010. Also see Bassett 2007, pp. 256–7, 260
  9. ^ Bassett 2007, p. 258
  10. ^ Lee Boysel; Joseph P. Murphy (April 1970). "Four-phase LSI logic offers new approach to computer designer". Computer Design: 141–146.
  11. ^ Bassett 2000, p. 115
  12. ^ "Court Room Demonstration System 1969 AL1 Microprocessor", 4/3/95, Lee Boysel. From the Computer History Museum. Accessed on line June 11, 2010.
  13. ^ "Microprocessor Stories: Four-Phase Systems AL1". Computer History Museum. 2011.
  14. ^ "The Surprising Story of the First Microprocessors". 30 August 2016. Archived from the original on 4 October 2022. Retrieved 4 October 2022.

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