The 1970’s was a rush to design new and innovative processors, faster, more features, and more bits. Most of the processors were new designs, a few were single chip implementations of older mainframes (such as the TMS9900 and the Intersil 6100. At the same time there was a competition of 4-bit processors. Somewhat remarkable in 1976 considering 16-bit designs were now being released. The most famous was of course the AMD AM2901, which undoubtable won the battle. There were others, the MMI 6701 (a company which AMD would go on to merge with). Motorola had the MC10800, made in ECL and Intel made the ill-fated (probably since it was only 2-bits) Intel 3002 Processor. TI made the SBP0400 in I2L that enjoyed some success, but that apparently wasn’t enough. In 1976, the same year as the SBP0400, the 6701 and the AMD AM2901, TI released the SN74S481. This was a Schottky TTL 4-bit slice processor (and the SN74S482 sequencer for it). It was a bit different than its competition.
AMD is well known for its 2901 bit-slice processor of the 1970’s (being made well into the 1990’s), as well as the previously detailed AM29116 16-bit processor released in 1981. However, the 1980’s brought another AMD design as well, though not as complicated, it is no less interesting. In 1981, there was not a clear DSP (Digital Signal Processor) architecture, or really purpose built design. The Signetics 8X300 was well suited for such work, but was not inherently designed for it. DSP tasks were handled by other processors, or by completely custom designs. The AM29501 was not designed as a DSP, but it was marketed as a signal processor, at least for the first 5 years of manufacture. What the 29501 was, was a relatively fast, and pipelined, byte slice processor, basically a highly upgraded AM2901.
As the name suggests, the 29501 processes data 8-bits at a time, and as a slicer, it requires external program control (it lacks a PC (Program Counter) or sequencer). It has an 8-function ALU, and 6 sets of registers, which can be accessed independently, allowing for a pipelined architecture, multiple instructions may be issued before the first one is completed (as long as they don’t need the same resources). While the ALU is doing some addition, more data may be fetched, or output to one of the 3 8-bit buses. AMD designed the 29501 to be able to do advanced DSP work, and such work requires multiplication, which is something the ‘501 cannot do itself. The 29501, however, was explicitly designed to interface to the AM29516/7 16-bit multipliers. If a multiplication is needed the microprogram controller simply puts it on the multiplier bus and tells the 2951x to handle it. A fairly advanced system could be built by using a 29116 a 29516 as well as a 29501, building a complete pipelined DSP system. One of the first designs using the 29501 in such a way was a finger print recognition system, for matching images of fingerprints, a particularly intense DSP task for the 1980’s.
In 1974 Monolithic Memories Inc. (MMI) announced the 6701 bit slice device. At its heart the 6701 is a 4-bit ALU much like the 74181 TTL IC. The 6701 adds a register, and some other support circuitry on chip making it much more adaptable. The 6701 has an approximate complexity of 1000 gates (meaning it would replace 1000 gates worth of TTL). The 6701 was made on a bipolar process and ran at 5.2MHz. Later versions would up this speed to around 11MHz.
The 6701 continues on until around 1980 by which time the AMD 2901 bit-slice processor had come to completely dominate the market. The Soviets however cloned/modified the 6701 as the 1802VS1 through the 80’s and into the 1990’s.
In the 1970’s and the 1980’s the Soviets developed and successfully flew their own version of the Space Shuttle. It was called the Buran. In many ways it was an enhancements of the US Space Shuttle, based on what the Soviets saw as deficiencies in the US design. One of the biggest differences was the piloting. The US STS (Shuttle Transport System) was designed to be a crewed vehicle. The computers assisted the pilot/co-pilot in launch, orbit, and recovery. Many of the functions on the STS can be handled by the computers (the Flight Computers were based on the IBM System/4 Pi) but the pilot was needed to handle the rest. The Soviets, on the other hand, designed the Buran to be able to launch, orbit, and land fully automatically. This meant the computers has to be very robust, and the programming even more so. The computers had to respond quickly to chaning inputs, and be able to handle failures gracefully. While each mission would have a set profile, unknown conditions would cause deviations that the computers must detect, analyse, and properly handle. Preferably without wrecking the multi-billion ruble space craft.
The main computer of the Buran is actually 4 independent systems that receive the same inputs. The clock in generated externally (with 4 backups) so that each computer is in perfect time (the STS uses software to ensure the computers are in time, rather then hardware). Redundancy is achieved by the voting system. Each computers outputs are compared, if one computers output is different, it is automatically shut down, leaving the 3 remaining computers. These computers are powered by a clone of the DEC PDP-11. The Soviet’s ‘acquired’ a few PDP/11 systems and then copied and cloned them into many different systems. The most common is the 1801 a 5MHz NMOS PDP-11 type device. The Buran used the 1806, which is the CMOS version. Here is a general overview of the flight computer.
In addition to the 1806 there were many sub-systems with their own processors. Details on these are a bit thin, however looking at other Soviet space computer designs it is very likely that many of these used the 134IP3 series of ALUs (a clone of the 54L181 TTL 4-bit ALU). This chip is also used in the Argon-16 and Argon 16A computers of the Soyuz and Progress spacecraft that are still in use today. Bit-slice devices were used extensively for many Soviet designs as it gave them a great ability to design custom processors to meet the applications needs. The Argon-17, which was used for anti-ballistic missile work, was based on the 583 series, an 8-bi slice processor. The C100 and C101 computers (used as weapons computers on the MiG-29) also use a BSP design.
In August 1975 AMD introduced the ‘100 ns Bipolar microprocessor.’ This was a bit-slice device. Essentially a 4-bit ALU (like a 74181) with functionality (scratch pad memory and accumulator register) to make it work as a processor that could be scaled to any bit width (using the 2909 sequencer and 2910 controller). Being made in bipolar allowed for the high speed (10MHz at the time was pretty quick). The introduction of the 2901 also marked the beginning of the end to the competition int he bit-slice arena. A combination of marketing, second-sourcing, and a good product allowed AMD to completely dominate the bit-slice market. Even today most bit-slice designs are based on the 2901 from 35 years ago.
At the time there were several other bit-slice processors on the market. Intel had the 3002 (a 2-bit design), National’s IMP-8 and IMP-16, and the original TTL 74181 were all bit-slice devices. MMI (which AMD bought in the 1980’s) had introduced the 6701 4bit slice in 1974, a full year before AMD’s 2901. TI had the SBP0400A and Motorola the MC10800 (in ECL – 1976). So why with all this competition did AMD come to dominate?
Second sourcing is the licensing of a design to other companies for them to manufacture, market and sell it. Sometimes its simply a license to manufacture, sometimes it comes with technical assistance, or even complete mask sets to make the device. There are three main reasons this is done (or was done back in the day)
In the 1970’s making IC’s was a relatively new process, one with many bugs, and often reliability issues. Having a second source was a must to get a big design win. A system design would not want to design a system around a chip that may end up not being available, or not be available in the quantities needed. Having a second source to get the IC from alleviated this problem. It gave system designers a stable supply, regardless if the primary source could not keep up, or had a problem.
Second-sourcing helped solve distribution problems as well. A company may have an excellent design, but no way to sell it. Often this was a geography problem. American companies did not initially have a large presence, or distributors set up, in Europe or Japan. An American company would often second-source a design to a European company (such as Siemens or Thomson) solely to get their design distributed in that area.
One of the keys to a processors success is design wins. It can be the best processor on the market,. but if no one uses it, it will fail. Having additional companies make, and market the processor vastly increased its exposure. Second-source companies would also typically make development systems, and other support tools, as well as vast documentation for the processor. This helped ensure that engineers knew about the processor, how to use it, and whee to get it, ensuring its winning of more sockets.
AMD clearly understood the importance of second-sourcing. In November 1975, just months after the 2901 was released, they designed an agreement with Motorola to make the 2901. In December, they signed up Raytheon, and in March of 1976 AMD signed an agreement with the SESCOSEM division of Thomson-CSF, to make and distribute the 2901 in markets outside the US and Japan. In June 1976 AMD amended their agreement with Motorola to include more technical assistance, ensuring Motorola could get the 2901 to market. In September 1976 MMI canceled the 6701, as they were unable to compete. MMI had no second-sources for the 6701 which likely led to its failure.
As the years went by, AMD added more second-sources, and dropped a few. Eventually coming to completely dominate the bit-slice market. The Soviets began to copy the 2901 around 1985 (not particularly legally but they did what they had to) and continued to do so until well into the 90’s.
|1976||Motorola, Raytheon, Thomson|
|1977||Motorola, Raytheon, Thomson, National|
|1978||Motorola, Raytheon, National, Fairchild, NEC, Signetics, Thomson|
|1980||Motorola, Raytheon, National, Fairchild, NEC, OKI (MSM8821?), Thomson|
|1982||Motorola (2903), National, Fairchild, NEC, Thomson|
|1985||National, Thomson, Cypress, USSR|
|1990||Cypress, IDT, Thomson, National, USSR|
|1995||Cyrpress, IDT, WSI, Thomson, Russia|
AMD also made the AM29C101 which was 4 2901s in a single chip, producing a 16bit processor. Cypress manufactured a copy of the 29C101 called the CY7C9101
Several other companies also designed multiple 2901s into a single chip. WSI (and later InnovASIC) designed the 59032, which has the equivalent of 8 2901s to form a 32 bit slice and the 59016 which was 16bit slice (4x 2901). IDT designed the 49C402 which was also a 16 bit slicer. Today the 2901 is still in wide use, and while not generally used for new designs, it still powers a vast amount of electronic equipment that still is in use. InnovASIC still manufactures the 2901 (in 59032 form) to this day.
Just last month an Apple 1 computer sold on eBay for almost $23,000. Today, the father of the PC, and where Steve Jobs got many of his inspirations (as did Bill Gates and numerous other founders of the computer industry), sold on eBay for a bit over $30,000.
The Xerox Alto was really the first modern computer as we know it. It was developed at the PARC research center, and had Ethernet, a mouse, a GUI, and assorted other things we are rather use to now. The date? 1973. Xerox did not understand the significance of what they had. They made over 2000 Altos of various configurations, but never sold them, most were simply given away to friends, workers, and universities.
Though never sold, the Alto’s value in the 1970s was $32,000 or so, not a far cry (disregarding inflation) of what a non-working one just sold for on eBay
The Alto was powered by a custom16-bit bit-slice processor consisting of 4 TTL 74181 ALU’s one of the first uses of the 74181, which was itself the first single chip ALU.
The 74181 consisted of around 75 gates, and could perform 16 arithmetic functions and 16 logic functions on a pair of 4-bit inputs. It was, for its time, very fast, much faster then most of the single chip processors of the time. A 74S181 like shown here, using Schottky technology, could operate at up to 90MHz or so. Obviously in a computer like the Alto actual clock speed would be reduced to match what the memory could do, which in the Alto, with its 128K of RAM, worked out to 5.8MHz.
Often times its easier, and cheaper to break a big job down into smaller more manageable chunks. The same goes for processing, and back in the 70’s and 80’s was fairly common. ‘Wider’ processors were available, but were expensive and often not very flexible. Bit slice processors were invented to fix this. a BSP is essentially an ALU (Arithmetic Logic Unit) that was 2 or 4 bits wide. They could be put in parallel though to make processors of any width you needed. intructions and control would then be fed to them by a control/sequencer chip. Perhaps the most famous was the AMD 2901, a 4 bit slice device which is still in production today by companies like Innovasic.
Intel also made a BSP, called the 3002. It was 2-bit slice processor and was second sourced by Signetics, as well as Intersil. Released in September of 1974, it was clocked at 6MHz, very fast for the time, and another reason BSP’s were so popular. Above is a Signetics made 3002 in an all white ceramic package. Fairly unusual in that the lid is also white.
Back in the day of CPU’s National was on the forefront of CPU design, while Intel was messing around with 4 and 8 bit designs. It by itself was the 4th CPU, and the 1st bit slice device.
It consists of:
4 x 4 bit IMP-00A/520D – These are the Register and Arithmetic Units
1 x IMP16A-521D – Standard 16 bit Instruction set control chip (Based on the Data General Nova)
1 x IMP16A-522D – Extended 16 bit Instruction set (not sure what addition instructions it has)
These were sold in a set by National, and in a pretty nice box.
Later on National implemented them as a single chip, the IMP16A-500D PACE, and then the NMOS INS8900.
More infomation about the IMP16 can be found at Antique Tech