Atlas (computer) facts for kids

Kids Encyclopedia Facts

This page is about a British supercomputer. For the early American codebreaking computer also known as Atlas, see UNIVAC 1101.

Quick facts for kids
Atlas Computer
The University of Manchester Atlas in January 1963
Product family	Manchester computers
Release date	1962
Units sold	3 (+ 3 Atlas 2)

The Atlas Computer was one of the world's first supercomputers. It was used from 1962 to 1972. When it was first built, many people said it was the most powerful computer in the world. Atlas was so important that people joked when it was turned off, half of the UK's computer power disappeared! It was also the first computer to use 'virtual memory'. This smart idea helps computers use memory better. Now, almost all computers use it!

Atlas was a 'second-generation' computer. This means it used small electronic parts called transistors. It was built by the University of Manchester, Ferranti, and Plessey companies working together. Two more Atlas computers were made. One went to British Petroleum and the University of London. The other went to the Atlas Computer Laboratory near Oxford.

A similar computer called the Titan (or Atlas 2) was built for Cambridge University. It had a different memory system. It also used a special operating system for sharing computer time. Two more Atlas 2 computers were delivered. One went to the CAD Centre in Cambridge. The other went to the Atomic Weapons Establishment.

The Atlas computer at the University of Manchester was turned off in 1971. The last Atlas computer was switched off in late 1976. Some parts of the Chilton Atlas are kept by National Museums Scotland. The main control desk was found in 2014. It is now at Rutherford Appleton Laboratory near Oxford.

History of the Atlas Computer
How Atlas Worked
See also

History of the Atlas Computer

Why was Atlas needed?

In the mid-1950s, people in the UK worried they were falling behind the US. The US was building much faster computers. In 1956, a Ferranti company expert said UK computers were slow. Even the fastest ones were much slower than American machines.

During this time, Tom Kilburn's team at Manchester University was experimenting. They were building small computers using transistors. This was a new and better way to build computers. In late 1956, Kilburn asked possible customers what they wanted. Many businesses needed to connect to many different devices. The Atomic Energy Authority wanted a computer that could do one million instructions per second. This idea led to the name MUSE, which meant 'microsecond engine'.

It was hard to make a computer that was both fast and connected to many devices. For example, a program reading from a card reader spends most of its time waiting. To fix this, the new computer needed more memory. It also needed a special operating system. This system would help manage the flow of data.

How Muse became Atlas

A committee heard about new, super-fast US computers. These were the Univac LARC and IBM STRETCH. They got the attention of the National Research Development Corporation (NRDC). This group helped move new technologies to the market. For about a year and a half, they had many meetings. They talked with customers, engineers, and design teams.

Even with all this work, there was no money from the NRDC by mid-1958. Kilburn decided to build a smaller MUSE himself. He wanted to test new ideas. He used money from renting out time on the University's Mark 1 computer. Soon after, in October 1958, Ferranti decided to join the project. In May 1959, they received a grant of £300,000 from the NRDC. This money would be paid back from sales. At some point, the computer was renamed Atlas.

The detailed design was finished by the end of 1959. Work on the compilers (programs that translate code) was moving along. But the Supervisor operating system was behind schedule. David Howarth, new to Ferranti, expanded the operating system team. The team grew from two to six programmers. They worked very hard, led by Howarth. They finally delivered the Supervisor. It had 35,000 lines of code. It could handle many programs at once. This helped with managing all the connected devices.

Where Atlas was installed

The first Atlas computer was built at the university in 1962. It had to be ready by December. The Atlas met this goal. It was officially started on December 7 by John Cockcroft. This system had an early version of the Supervisor. It only had a compiler for Autocode. The final Supervisor version was installed in January 1964. It also had compilers for ALGOL 60 and Fortran.

By the mid-1960s, the original Atlas was used almost all the time. It ran for 20 hours a day. During this time, it might run up to 1,000 programs. The computer's time was split between the University and Ferranti. Ferranti charged its customers £500 an hour. Some of this money went back to the University. In 1969, the computer time the University used was worth £720,000. The machine was turned off on November 30, 1971.

Ferranti sold two more Atlas computers. One went to a group of London University and British Petroleum in 1963. Another went to the Atomic Energy Research Establishment in December 1964. This computer was later moved to the Atlas Computer Laboratory. This made it easier for people to use. This Atlas became the largest one. It had 48,000 words of memory and 32 tape drives. Time on it was available to all UK universities. It was turned off in March 1974.

Titan and Atlas 2

In February 1962, Ferranti gave some Atlas parts to Cambridge University. In return, the University would use them to make a cheaper version. This led to the Titan machine. It started working in the summer of 1963. Ferranti sold two more of this design as Atlas 2. One went to the Atomic Weapons Research Establishment in 1963. The other went to the government's Computer Aided Design Center in 1966.

Atlas's lasting impact

Atlas was designed to compete with the US LARC and STRETCH computers. Both LARC and STRETCH were officially used before Atlas. But Atlas was much faster than LARC. It was about four times quicker. Atlas was only slightly slower than STRETCH. Even so, a Ferranti manager said in 1962 that Atlas was the world's most powerful computer. He believed it would finish jobs faster than any rival.

No more LARC computers were sold. It is not clear how many STRETCH machines were made.

The Atlas was not truly beaten until the CDC 6600 arrived in 1964. CDC later said that a 1959 description of Muse helped them. It sped up the development of the 6600. This helped CDC win a contract in Australia. Australia had first planned to buy an Atlas.

Ferranti had money problems in the early 1960s. They sold their computer division to International Computers and Tabulators (ICT) in 1963. ICT decided to focus on mid-sized computers.

Many people in the computer world thought highly of Atlas. C. Gordon Bell of Digital Equipment Corporation praised it. He said Atlas showed many good design ideas. It could run many programs at once. It had a large memory space. It also introduced new ways to make instructions more powerful.

In June 2022, the Atlas Computer received an IEEE Milestone award. This award recognized its importance and the invention of virtual memory.

How Atlas Worked

Hardware details

The Atlas computer had many new features. Here are some key facts about it:

It used a 48-bit word size. A word could hold one number or instruction. It could also hold two addresses or eight characters.
It had a fast adder. This part of the computer added numbers quickly.
It had a large address space of 24-bit. This allowed it to access 16 million characters of memory.
It had 16,000 words of magnetic core memory. This was like 96 KB of fast memory.
It had 8,000 words of read-only memory (ROM). This held the main operating system programs.
It had 96,000 words of drum memory. This was like 576 KB. It worked with the core memory using virtual memory. Each 'page' of memory was 512 words.
It had 128 fast index registers. These helped change memory addresses.
It could connect to new peripherals like magnetic tape. It also had DMA for fast data transfer.
It used special memory addresses for controlling devices. This allowed for interrupts and special routines.
It had an associative memory. This helped find if a virtual memory location was in the fast core memory.
It used instruction pipelining. This helped it process instructions faster.

Atlas did not use a regular clock to time its operations. It was an asynchronous processor. So, measuring its exact speed was hard. But here are some examples:

Adding fixed-point numbers: 1.59 microseconds.
Adding floating-point numbers: 1.61 microseconds.
Multiplying floating-point numbers: 4.97 microseconds.

Extracode feature

One special feature of Atlas was "Extracode." This allowed complex instructions to be done by software. Special hardware helped start and finish these routines quickly. The Extracode programs were stored in ROM. This made them even faster.

The first ten bits of an Atlas instruction were the operation code. If the first bit was zero, it was a normal instruction. The hardware ran it directly. If the first bit was one, it was an Extracode. This was like a special jump to a program in the ROM. About 250 Extracodes were used.

Extracodes were similar to what we now call software interrupts or traps. They were used for math calculations. These calculations would have been too slow for the hardware alone. Examples include sine, logarithm, and square root. About half of the Extracodes were for the Supervisor. These called operating system programs. For example, "Print a character" or "Read data from tape." Extracodes were the only way a program could talk to the Supervisor. Other UK computers of that time had similar ways to use their operating systems.

Software innovations

Atlas led the way for many software ideas still used today. This includes the Atlas Supervisor. Many people think it was the first modern operating system.

One of the first high-level languages on Atlas was Atlas Autocode. It was made to fix some issues with another language called Algol 60. But Atlas also supported Algol 60, Fortran, and COBOL. It also had ABL (Atlas Basic Language), which was close to machine language. Since it was a university computer, many students used it. They could develop programs in a safe environment.

Several of the compilers were written using the Compiler-compiler. This was thought to be the first of its kind.

Atlas also had a programming language called SPG (System Program Generator). An SPG program could write more code for itself while running. It could also define and use macros. Its variables used angle brackets. It also had a text parser. This made SPG programs look a bit like a special code format.

Hardware and software working together

From the very beginning, Atlas was designed as a supercomputer. It was meant to have a complete operating system. The hardware had special features to help the operating system work. For example, Extracode routines and interrupt routines had their own memory and registers. This made it very fast to switch between different modes of operation.