Ferranti Sirius facts for kids

Ferranti's Sirius was a small computer released in 1961. It actually started working in 1959, and companies could rent time on it.

The Sirius was made for smaller offices that didn't have special computer experts. It used decimal numbers (like we do) instead of binary (0s and 1s), which made it easier to program. It also used a special programming language called Autocode.

This computer was designed to fit right behind a normal office desk. It ran on regular UK electricity (240 volts) and didn't need any special cooling. It wasn't the fastest computer, doing about 4,000 operations per second, and its memory was limited. However, Ferranti said its price was very good for what it could do.

History of the Sirius

Early Ideas: Magnetic Amplifiers

In the 1950s, scientists were very interested in using "magnetic amplifiers" as a new way to build computer parts. These amplifiers used special magnetic cores to switch signals on and off, like a light switch. This was a "solid state" way of doing things, meaning it didn't use old-fashioned vacuum tubes.

The idea was that these magnetic parts could add up different signals and then give a single answer. This was a bit like how people vote, where many inputs lead to one decision. One cool thing was that you could thread many wires through these magnetic cores. This was useful for making complex logic circuits, like those needed for adding numbers.

However, magnetic amplifiers didn't last long. When they were first studied, transistors were expensive and not very reliable. But by the late 1950s, new ways of making transistors made them cheaper and much better. Because of this, magnetic amplifiers quickly disappeared, and only a few computers were ever built using them.

The "Neuron" Idea

A team at Ferranti's research lab in Manchester, led by Gordon Scarrott, had worked with magnetic amplifiers. This team had a long history of working with Manchester University on early computers.

As transistors became cheaper, an engineer named Ken Johnson at the lab had a new idea. He proposed a new type of transistor-based logic called "Neuron." This system used transistors in a way that was similar to the magnetic amplifiers. It was special because it often needed only one transistor for each logic part, while other designs needed two or more. Since transistors were still somewhat expensive, a computer built with Neuron could be much cheaper. Johnson called it "Neuron" because it worked a bit like the neurons in our brains.

Everyone was excited about Neuron. The team decided to build a small test computer called "Newt" (short for "Neuron test"). Newt worked well, and the lab was so impressed that they decided to build a full computer using the Neuron design. This led to the Sirius.

The Sirius was much cheaper than other computers of its time that used traditional transistor logic. It was announced on May 19, 1959. Ferranti claimed it would be the smallest and most affordable computer in Europe. The Sirius sold for about £20,000 in England. This was a great deal compared to its rivals, like the Elliott 803 at £35,000 and the ICT 1301 at £120,000. About 20 Sirius computers were made in total.

The Orion Computer

Ferranti's research team believed Neuron was a huge step forward. They decided to build an even bigger computer using the same logic, hoping it would also be much cheaper than other large machines. This new computer, called the Ferranti Orion, was meant for big businesses. Large insurance companies, like Prudential plc, signed up to be early customers.

However, the Orion, which came out in 1961, turned out to be a big problem. Because it was much larger than the Sirius, it had longer wires inside. This meant the Neuron circuits needed more electrical current to work. Electrical noise and timing issues became a big problem, making the Orion much slower than promised.

Engineers at other Ferranti offices had worried about the Neuron design from the start. When the Orion failed, these teams convinced Prudential that they could build a new machine five times faster for the same price within three years. They redesigned the computer from scratch using traditional transistor logic. This new machine became the Orion 2 in 1964. However, the problems with the first Orion project caused too many financial losses for Ferranti. Because of this, their computer divisions were sold off to International Computers and Tabulators in October 1963.

How the Sirius Worked

The Sirius used decimal numbers, which means it stored numbers like 0, 1, 2, 3, etc., instead of just 0s and 1s (binary). Each decimal digit was stored using 4 binary digits, a system called "binary-coded decimal". This was very useful for many office tasks and was easy to do with the Neuron circuits. Numbers were stored as ten decimal digits in one of eight special memory areas called "accumulators".

The main memory of the Sirius was called a "single-level store." It used "torsional delay-line memory" elements. Imagine sending a signal down a wire, and it takes a little time to come back – that's how it stored data. Each of these elements could store 50 words. Most Sirius computers came with 1,000 words of memory, but you could add more cabinets to get up to 10,000 words. The first 200 words were usually used for common programs.

The computer used a simple set of instructions. Each instruction told the computer what to do and where to find the data in memory. For example, one instruction would subtract a number from an accumulator and put the result back. Since the Sirius used decimal numbers, it had special instructions to quickly multiply or divide numbers by 10, just by shifting them around. The Sirius also came with a version of Autocode, an early programming language. Programs written for the Ferranti Pegasus computer could often run on the Sirius with very few changes.

The Sirius operated at 500,000 cycles per second. However, because it processed numbers one digit at a time, adding or subtracting took about 240 millionths of a second. Overall, it could do about 4,000 operations per second. Multiplying or dividing took a bit longer, averaging about 8 thousandths of a second. Even though this might seem slow today, Ferranti proudly said that the Sirius was "nearly twice as fast as any other existing computer at its price."

To use the Sirius, an operator would use a box with 10 columns of number buttons. There were also command keys. The computer showed its results on two displays that used cool-looking nixie tubes, which are glowing glass tubes that show numbers. There was also a large electric clock on the front.

All Sirius computers came with a Ferranti TR5 or TR7 photo-electric paper tape reader, which could read 300 characters per second. They also had a slower Teletype paper tape printer. You could connect other devices like magnetic tape drives, punched card readers, and printers through special input and output channels.

The Sirius was designed to fit easily into small offices. It only needed 5 amps of standard 240-volt power, just like a regular appliance. It was 10 inches deep, 4 feet 9 inches high, and 6 feet 9 inches wide. This size was chosen so it could sit right behind a standard office desk. The power supply was even placed so it would fit into the knee space under the desk. The paper tape reader and input box usually sat on the desk, while the paper tape punch was a separate, larger machine.

The computer weighed about 560 pounds (254 kg).