Four-Phase Systems AL1

The AL1 was an early 8-bit microprocessor designed by Four-Phase Systems and first run in April 1969. It is the first single-chip central processing unit (CPU) to be produced,^[1][b] pre-dating the Intel 4004 by two years. Although it could be used as a stand-alone general purpose CPU, Four-Phase did not use it in this fashion at the time. Instead, they used three AL1's in a bit-slice system to produce a 24-bit minicomputer, the System IV/70. The company never advertised the AL1 as a product and did not sell it to other customers, the 4004 was the first design to be sold in standalone form.

In 1990, Texas Instruments began to enforce patents on the basic concept of a microprocessor, which they had initially filed in 1971. These plans were upset when a patent was granted to another designer, Gilbert Hyatt. The resulting flurry of lawsuits led to the AL1 becoming famous in 1995 when Lee Boysel built a small computer to demonstrate his design incorporated all of these concepts using a chip manufactured two years before TI's design and a year before Hyatt's.^[c]

Lee Boysel started work at Fairchild Semiconductor in 1966 after working at several other company's semiconductor departments. At Fairchild he worked on MOS design, which at that time was a very new concept. Over the next two years he developed several new MOS chips, including a 256-bit static RAM and an 8-bit adder. The adder was the first integrated circuit with over 100 gates.^[2]

Boysel left Fairchild in October 1968 to start his own company, Four-Phase Systems,^[3] which incorporated in February 1969.^[4] Corning Glass, who was at that time investing in the emerging semiconductor market, provided start-up funding of $2 million. Four-Phase was what would today be known as a fabless designer, using another Fairchild spin-off, Cartesian, as a semiconductor foundry.^[5]

The company name refers to the way the individual transistors in the MOS circuits were powered by the clock generator. This design allows the transistors to be made smaller, although it requires some additional design-time complexity to arrange them. Smaller transistors translates to cheaper ICs, which he intended to use to build lower-cost computers that would compete with systems from Data General and the mid-range machines from IBM.^[5]

The first engineering samples of the AL1 were available in 1970. Three AL1s were each paired with a read only memory (ROM), a random logic chip that ran the bus, and the external clock generator onto a board to produce the 24-bit CPU for the System IV/70.^[5] The company never sold the AL1 or the complete processor boards, nor did they file patents on the design, but they did publish an article in the April 1970 issue of Computer Design magazine describing the design and how it could be used to build a simple computer.^[6]

The IV/70 was successful, selling for about half the equivalent machines from other major vendors. By the mid-1970s they had sold 350 systems, and by 1980 they had 5000 employees and annual sales over $250 million. When sales of the AL1-based systems dwindled by the late 1970s, the firm introduced a series of Unix-based computers based on the Motorola 68000, which led to Motorola purchasing the company in 1982.^[2]

In 1970, Datapoint corporation (then known as CTC), sent a contract to Intel asking them for a ways to reduce the complexity and heat production of the processor in their Datapoint 2200 smart terminal. Intel responded in June 1970 with a proposal to build a single-chip version of the entire processor, a design that would later be known as the Intel 8008. They mentioned the concept in an advertisement in October 1970. Texas Instruments (TI) heard of the contract and asked Datapoint if they could bid on it too, initially pitching a three-chip design. Datapoint pointed out that Intel had a single-chip solution, and around April 1970 TI responded by proposing a single-chip solution of their own, the TMX 1795, which was first made public in March 1971.^[7]

Datapoint ultimately chose neither design, as they solved the heat problems on their own, and both chips were much slower than the upcoming parallel TTL-based design. At that point, both companies were released from the contract.^[7] TI decided to abandon their chip,^[8] while Intel instead launched it commercially in April 1972. TI did, however, begin filing patents on the design, while Intel's lawyers told them not to bother because the idea was too obvious to receive a patent.^[7] TI received several patents, including a major one in 1983.^[7] 1986, TI began demanding royalties from every company making microprocessors, amounting to 2 to 3% of the cost of every computer.^[9] This launched a series of lawsuits in what became known as "TI vs. Everyone".^[10]

Further confusing the issue was the 1990 award of a December 1970 patent on a "Single Chip Integrated Circuit Computer Architecture" to Gilbert Hyatt, which pre-dated TI and apparently rendered their patents moot.^[11] This new wrinkle had the side-effect of causing all of the law firms involved to begin looking for additional prior art. This led to Boysel being called as an expert witness by no less than twenty-five of the law firms involved, as his article in April 1970 pre-dated all of these claims. TI admitted that they were aware of the 1970 article, but, as in the case of Hyatt, they claimed that it wasn't a "real computer". This turned out to be a bad idea, as it made Boysel mad and determined to prove them wrong.^[6]

In order to drive home the point that the AL1 was indeed a system that incorporated all of the ideas TI was claiming, Boysel built a tiny computer system consisting of an AL1, with its 1969 manufacturing date still clearly stamped on it, mounted on a plexiglass card. This was connected to RAM, ROM, an I/O unit housed in cartridges from the Nintendo Entertainment System.^[12] The ROM held a simple program from Datapoint for customer lookups called WSTR, which had been given to TI and used to validate the TMX 1795. The only difference was that the AL1 ran the program ten times faster than the TI or Intel chips.^[13]

Boysel noted that when he described the demo just prior to the trial's scheduled start date:

Faces went white; the place turned into chaos. They just realized that they’d lost, and it was over.^[6]

The system Boysel built was designed to counter a specific part of the TI claims. Their claims used a diagram that showed a complete computer consisting of the IC, a ROM, I/O devices, and optional RAM. Boysel's system was built to show that one could build that precise illustrated concept using the AL1.^[14] The demonstration was apparently convincing, and the trial was abandoned.^[7]

Since the trial, others have questioned whether the demonstration allows the AL1 to be described as a "true" microprocessor. In particular, Ken Shirriff, a noted retrocomputing expert, notes that the system only worked because the ROM contained the sequencing code that would normally be located on the processor itself, meaning that it could not run on its own without an external ROM. So, depending on the definition of "microprocessor", the AL1 may or may not be the first.^[7]

On the other hand, Nick Tredennick, formerly the lead designer of the Motorola 68000, stated "I have looked at [the] AL1 design from the papers written about it through the circuit diagrams and discussions with Lee Boysel and I believe it to be the first microprocessor in a commercial system."^[8] Gordon Bell also supports this position.^[8]

The AL1 was fabricated using the then-current 10 micron process, the same used by the Intel 4004 and other designs of the era. However, the four-phase logic allowed them to place over 1,000 gates (~4000 transistors) on a 130 by 120 mil (100 mm²) chip. In comparative terms, the chip was as complex as the Intel 8008 but the same size as the 4004, and also ran at a much higher speed of 1 MHz, compared to 740 kHz for the 4004 or 500 kHz for the 8008.^[5]

An additional improvement was in the packaging. The 4004 was packaged in a 16-pin dual in-line package (DIP) and the 8008 in a 18-pin DIP. This is too few pins to allow data and memory addresses to be expressed at the same time, meaning that accessing memory requires several cycles. The AL1 was packaged in a 40-pin DIP, which allowed it to access memory in a single cycle. This would be a common size for later CPU designs. The wider busses and higher operating speed meant the AL1 was almost 10 times the speed of any other design of the era.^[5]

The AL1 was an 8-bit design with eight processor registers, one of which was used as the program counter, feeding an 8-bit arithmetic logic unit (ALU).^[5]

• Boysel, Lee (3 April 1995). "Court Room Demonstration System 1969 AL1 Microprocessor" (PDF). Computer History Museum.
• Culver, John (15 August 2014). "Four-Phase Systems AL1 Processor – 8-bits by Lee Boysel". The CPU Shack.
• Plutte, Jon (2011). "Microprocessor Stories: Four-Phase Systems AL1". Computer History Museum.
• Faggin, Federico. "The Intel 4004 Microprocessor and the Silicon Gate Technology". Intel 4004.
• Hertz, Jake (7 September 2023). "How the 1969 AL1 Microprocessor Settled a Silicon Valley Court Drama". All About Circuits.
• June, Catharine (21 November 2007). "Lee Boysel: the early history of microprocessing". University of Michigan, Electrical and Computer Engineering.
• Laws, David (20 September 2018). "Who Invented the Microprocessor?". Computer History Museum.
• Lee, Don; Kaplan, Karen (20 June 1996). "Patent Office Ruling Favors TI, Firm Says". Los Angeles Times.
• Pollack, Andrew (16 October 1990). "A Chip Maker's Profit on Patents". New York Times.
• Shirriff, Ken (May 2015). "The Texas Instruments TMX 1795: the (almost) first, forgotten microprocessor".