Ferranti Sirius
Encyclopedia
Ferranti
's Sirius was a small business computer released in 1961. Designed to be used in smaller offices without a dedicated programming staff, the Sirius used decimal arithmetic instead of binary, supported Autocode
to ease programming, was designed to fit behind a standard office desk, and ran on U.K. standard mains electricity (then 240 V) with no need for cooling. It was also fairly slow, with instruction speeds around 4,000 operations per second, and a main memory based on delay lines
, but as Ferranti pointed out, its price/performance ratio
was difficult to beat.
s as a solid state
switching device. The amplifiers used the saturation points and hysteresis
curves of a magnetic core
to sum a number of inputs and settle to a single output state. The various logical functions were achieved by linearly adding the input signals on control lines and generating an output signal if the sum exceeded a fixed threshold, defined by the saturation property of the magnetic core. This process came to be known as "Ballot Box Logic" due to the way the inputs "voted" on the output. One difference between magnetic logic and conventional tube or transistor systems is that it is the current that defines the logic levels, not voltage.
Since the magnetic cores were open in the middle, any number of control lines could be threaded through them. This was particularly useful when implementing a "best two out of three", a common logic circuit used in binary adders. Another possibility is to use the same core as the switching element in several different portions of the machines logic. For instance, a single core could be used as part of the system that reads instructions from memory, and then again as part of the ALU
, as long as both functions don't operate at the same time (as they would in an instruction pipeline
).
Interest in magnetic amplifiers lasted only a short time through the 1950s. When they were first being studied, transistor
s were expensive and unreliable devices, but the introduction of new manufacturing techniques in the late 1950s started to address both of these problems. In spite of their other advantages, magnetic amplifiers quickly disappeared as transistor based logic became increasingly common, and only a few computers based on these systems were produced.
and several follow-on designs.
As the prices of transistors dropped, Ken Johnson, an engineer at the lab, proposed a new type of transistor-based logic that followed the same conventions as the magnetic amplifiers, namely that binary logic was based on well known currents instead of voltages. Like the magnetic amplifiers, Johnson's "Neuron" design could be used to control several different inputs. Better yet, the system often required only one transistor per logic element, whereas conventional voltage-based logic often required two or more. Although transistors were falling in price they were still expensive, so a Neuron based machine might offer similar performance at a much lower price.
Interest in Neuron was high, and the team decided to build a small machine to test it, known as "Newt",
for "Neuron test". This machine was successful, and the lab was so impressed that they decided to expand the testbed into a complete computer. The result was the Sirius, which was much less expensive than similar machines using traditional transistor logic. Sirius was announced on 19 May 1959 with claims that it would be the smallest and most economically priced computer in the European market. The Sirius was marketed in England for ₤20,000, a deal compared to its competitors, the Elliott 803
at ₤35,000 and the ICT 1301
at ₤120,000 pounds. About 20 were produced in total.
signed up as a launch customer while several other large insurance firms followed. Emerging as the Ferranti Orion
in 1961, the system proved to be a disaster. As the machine was much larger than the Sirius physically, it had longer wire runs and thus required larger currents to operate the Neurons. Electrical noise and settling times were major issues, and Orion was much slower than promised.
Engineers at other Ferranti offices were concerned about the Neuron-based design from the start, but were never able to convince management to stop the effort. When Orion failed, these teams were able to convince Prudential that they could deliver a machine five times as fast at the same price point within three years. A ground-up redesign using traditional transistor logic followed and emerged in 1964 as the Orion 2. However, the losses caused by the Orion project were too great for management's taste, and the computer divisions had already been sold off to International Computers and Tabulators
in October 1963.
s, along with a parity bit. The computer words could also be used to store half of a double-length number, or five characters.
The accumulators were backed by what Ferranti called a "single-level store", a main memory formed out of a series of torsional delay line memory
elements storing 50 words each. Machines were normally supplied with 1,000 words, but this could be expanded through additional cabinets with 3,000 words each to a reach a total of 10,000 words. Normally the first 200 words were used to store library routines.
The instruction set
was a single-address format stored in single decimal digits of a word, containing a 6-digit address, a 2-digit instruction code, and 1-digit specifying the "A" and "B" accumulators. In most instructions the contents of the B register, treated as an index register, were added to the address field and the contents of that memory location were processed and output to A. For instance, instruction "01" subtracted the contents of the addressed location from A and wrote the result back to A. As the Sirius used decimals for storage, the system offered a number of instructions that quickly multiplied the input or output by 10, by shifting the numbers in the accumulators. The Sirius was also supplied with a version of Autocode
adapted from the Ferranti Pegasus, and Autocode programs from the Pegasus could be run on the Sirius "with very little alteration."
The computer operated at 500 kHz, but because each digit was stored as 4 bits, the basic word operational cycle was 80 microseconds. The ALU
was serial, so addition or subtraction took 240 microseconds, and overall processing speed was about 4,000 operations a second. General multiplication or division took between 4 and 10 milliseconds, averaging 8. Although this is relatively slow, even for the era, Ferranti boasted that "The Sirius computer is nearly twice as fast as any other existing computer at its price, both as regards speeds of input and output and speeds of computation."
Operator input was provided in the form of a box with 10 columns of digits in the center with buttons for each number from 0 to 10. A single column on the left was used to select an accumulator, and the other than to input the ten digit value. There was a row of command keys on the right. Output consisted of two ten-digit displays using nixie tubes on the front of the machine, which also featured a large electric clock.
All machines were also supplied with a Ferranti TR5 or TR7 photo-electric paper tape reader that read at 300 characters a second, and a slower Teletype paper tape printer (no speed is given, likely 110). Further input/output
was offered through two input and two output channels, normally connected to a five-way switch box that allowed the operator to select which devices were fed to which channels. Magnetic tape
, punched card
, printers and other common I/O devices were supported through these channels.
The machine was designed to fit into small offices with a minimum of support. It required 5 amps of standard 50 Hz 240 V mains power, the only concern being that it was "free from excessive fluctuations." The case was only 10 inches deep, 4 foot 9 inches high, and 6 foot 9 inches across. This size was chosen to allow it to be placed directly behind a standard office desk, and the power supply was positioned so it projected into the knee-hole area. The reader and input box were normally placed on the desk, while the paper tape punch, a relatively large machine, was separate and sized to provide an even desktop.
Ferranti
Ferranti or Ferranti International plc was a UK electrical engineering and equipment firm that operated for over a century from 1885 until it went bankrupt in 1993. Known primarily for defence electronics, the Company was once a constituent of the FTSE 100 Index but ceased trading in 1993.The...
's Sirius was a small business computer released in 1961. Designed to be used in smaller offices without a dedicated programming staff, the Sirius used decimal arithmetic instead of binary, supported Autocode
Autocode
Autocode is the name of a family of "simplified coding systems", later called programming languages, devised in the 1950s and 1960s for a series of digital computers at the Universities of Manchester and Cambridge...
to ease programming, was designed to fit behind a standard office desk, and ran on U.K. standard mains electricity (then 240 V) with no need for cooling. It was also fairly slow, with instruction speeds around 4,000 operations per second, and a main memory based on delay lines
Delay line memory
Delay line memory was a form of computer memory used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay line memory was a refreshable memory, but as opposed to modern random-access memory, delay line memory was serial-access...
, but as Ferranti pointed out, its price/performance ratio
Price/performance ratio
In economics and engineering, the price/performance ratio refers to a product's ability to deliver performance, of any sort, for its price. Generally speaking, products with a higher price/performance ratio are more desirable, excluding other factors....
was difficult to beat.
Magnetic amplifiers
During the 1950s there was widespread interest in the use of magnetic amplifierMagnetic amplifier
The magnetic amplifier is an electromagnetic device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to vacuum tube amplifiers where robustness and high current capacity were required...
s as a solid state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
switching device. The amplifiers used the saturation points and hysteresis
Hysteresis
Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
curves of a magnetic core
Magnetic core
A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, inductors and magnetic assemblies. It is made of ferromagnetic metal such...
to sum a number of inputs and settle to a single output state. The various logical functions were achieved by linearly adding the input signals on control lines and generating an output signal if the sum exceeded a fixed threshold, defined by the saturation property of the magnetic core. This process came to be known as "Ballot Box Logic" due to the way the inputs "voted" on the output. One difference between magnetic logic and conventional tube or transistor systems is that it is the current that defines the logic levels, not voltage.
Since the magnetic cores were open in the middle, any number of control lines could be threaded through them. This was particularly useful when implementing a "best two out of three", a common logic circuit used in binary adders. Another possibility is to use the same core as the switching element in several different portions of the machines logic. For instance, a single core could be used as part of the system that reads instructions from memory, and then again as part of the ALU
Arithmetic logic unit
In computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations.The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
, as long as both functions don't operate at the same time (as they would in an instruction pipeline
Instruction pipeline
An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput ....
).
Interest in magnetic amplifiers lasted only a short time through the 1950s. When they were first being studied, 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...
s were expensive and unreliable devices, but the introduction of new manufacturing techniques in the late 1950s started to address both of these problems. In spite of their other advantages, magnetic amplifiers quickly disappeared as transistor based logic became increasingly common, and only a few computers based on these systems were produced.
Neuron
One group working on the magnetic amplifier design was Gordon Scarrott's team at Ferranti R&D labs in West Gorton, Manchester. This team had a longstanding partnership with Manchester University, after commercializing the Manchester Mark 1Manchester Mark 1
The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester from the Small-Scale Experimental Machine or "Baby" . It was also called the Manchester Automatic Digital Machine, or MADM...
and several follow-on designs.
As the prices of transistors dropped, Ken Johnson, an engineer at the lab, proposed a new type of transistor-based logic that followed the same conventions as the magnetic amplifiers, namely that binary logic was based on well known currents instead of voltages. Like the magnetic amplifiers, Johnson's "Neuron" design could be used to control several different inputs. Better yet, the system often required only one transistor per logic element, whereas conventional voltage-based logic often required two or more. Although transistors were falling in price they were still expensive, so a Neuron based machine might offer similar performance at a much lower price.
Interest in Neuron was high, and the team decided to build a small machine to test it, known as "Newt",
for "Neuron test". This machine was successful, and the lab was so impressed that they decided to expand the testbed into a complete computer. The result was the Sirius, which was much less expensive than similar machines using traditional transistor logic. Sirius was announced on 19 May 1959 with claims that it would be the smallest and most economically priced computer in the European market. The Sirius was marketed in England for ₤20,000, a deal compared to its competitors, the Elliott 803
Elliott 803
The Elliott 803 was a small, medium speed digital computer manufactured by the British company Elliott Brothers in the 1960s. About 250 were built and most British universities and colleges bought one.-History:...
at ₤35,000 and the ICT 1301
ICT 1301
The ICT 1301 and its smaller derivative ICT 1300 were early business computers from International Computers and Tabulators. Typical of mid-sized machines of the era they used core memory, drum storage and punched cards, but they were unusual in that they were based on decimal logic instead of...
at ₤120,000 pounds. About 20 were produced in total.
Orion
Convinced that Neuron was a major advance, Ferranti R&D proposed a much larger machine based on the same logic, one that would have even greater price advantages over traditional designs. The new machine was aimed at the business market, not their traditional high-performance niche, and Prudential plcPrudential plc
Prudential plc is a multinational financial services company headquartered in London, United Kingdom.Prudential's largest division is Prudential Corporation Asia, which has over 15 million customers across 13 Asian markets and is a top-three provider of life insurance in mainland China, Hong...
signed up as a launch customer while several other large insurance firms followed. Emerging as the Ferranti Orion
Ferranti Orion
The Orion was a mid-range mainframe computer introduced by Ferranti in 1959 and installed for the first time in 1961. Ferranti positioned Orion to be their primary offering during the early 1960s, complementing their high-end Atlas and smaller systems like the Sirius and Argus...
in 1961, the system proved to be a disaster. As the machine was much larger than the Sirius physically, it had longer wire runs and thus required larger currents to operate the Neurons. Electrical noise and settling times were major issues, and Orion was much slower than promised.
Engineers at other Ferranti offices were concerned about the Neuron-based design from the start, but were never able to convince management to stop the effort. When Orion failed, these teams were able to convince Prudential that they could deliver a machine five times as fast at the same price point within three years. A ground-up redesign using traditional transistor logic followed and emerged in 1964 as the Orion 2. However, the losses caused by the Orion project were too great for management's taste, and the computer divisions had already been sold off to International Computers and Tabulators
International Computers and Tabulators
International Computers and Tabulators or ICT was formed in 1959 by a merger of the British Tabulating Machine Company and Powers-Samas. In 1963 it also added the business computer divisions of Ferranti...
in October 1963.
Description
The Sirius was based on decimal numbers stored as 4 binary digits each, a useful design for many tasks that the Neuron circuits allowed to be implemented inexpensively. Numbers were stored as a string of ten decimal digits in one of eight accumulatorAccumulator (computing)
In a computer's central processing unit , an accumulator is a register in which intermediate arithmetic and logic results are stored. Without a register like an accumulator, it would be necessary to write the result of each calculation to main memory, perhaps only to be read right back again for...
s, along with a parity bit. The computer words could also be used to store half of a double-length number, or five characters.
The accumulators were backed by what Ferranti called a "single-level store", a main memory formed out of a series of torsional delay line memory
Delay line memory
Delay line memory was a form of computer memory used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay line memory was a refreshable memory, but as opposed to modern random-access memory, delay line memory was serial-access...
elements storing 50 words each. Machines were normally supplied with 1,000 words, but this could be expanded through additional cabinets with 3,000 words each to a reach a total of 10,000 words. Normally the first 200 words were used to store library routines.
The instruction set
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
was a single-address format stored in single decimal digits of a word, containing a 6-digit address, a 2-digit instruction code, and 1-digit specifying the "A" and "B" accumulators. In most instructions the contents of the B register, treated as an index register, were added to the address field and the contents of that memory location were processed and output to A. For instance, instruction "01" subtracted the contents of the addressed location from A and wrote the result back to A. As the Sirius used decimals for storage, the system offered a number of instructions that quickly multiplied the input or output by 10, by shifting the numbers in the accumulators. The Sirius was also supplied with a version of Autocode
Autocode
Autocode is the name of a family of "simplified coding systems", later called programming languages, devised in the 1950s and 1960s for a series of digital computers at the Universities of Manchester and Cambridge...
adapted from the Ferranti Pegasus, and Autocode programs from the Pegasus could be run on the Sirius "with very little alteration."
The computer operated at 500 kHz, but because each digit was stored as 4 bits, the basic word operational cycle was 80 microseconds. The ALU
Arithmetic logic unit
In computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations.The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
was serial, so addition or subtraction took 240 microseconds, and overall processing speed was about 4,000 operations a second. General multiplication or division took between 4 and 10 milliseconds, averaging 8. Although this is relatively slow, even for the era, Ferranti boasted that "The Sirius computer is nearly twice as fast as any other existing computer at its price, both as regards speeds of input and output and speeds of computation."
Operator input was provided in the form of a box with 10 columns of digits in the center with buttons for each number from 0 to 10. A single column on the left was used to select an accumulator, and the other than to input the ten digit value. There was a row of command keys on the right. Output consisted of two ten-digit displays using nixie tubes on the front of the machine, which also featured a large electric clock.
All machines were also supplied with a Ferranti TR5 or TR7 photo-electric paper tape reader that read at 300 characters a second, and a slower Teletype paper tape printer (no speed is given, likely 110). Further 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...
was offered through two input and two output channels, normally connected to a five-way switch box that allowed the operator to select which devices were fed to which channels. Magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
, punched card
Punched card
A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...
, printers and other common I/O devices were supported through these channels.
The machine was designed to fit into small offices with a minimum of support. It required 5 amps of standard 50 Hz 240 V mains power, the only concern being that it was "free from excessive fluctuations." The case was only 10 inches deep, 4 foot 9 inches high, and 6 foot 9 inches across. This size was chosen to allow it to be placed directly behind a standard office desk, and the power supply was positioned so it projected into the knee-hole area. The reader and input box were normally placed on the desk, while the paper tape punch, a relatively large machine, was separate and sized to provide an even desktop.
Further reading
- "The advantages of the Ferranti Sirius Computer", Ferranti, 1961