Home > Atlas Computer (Manchester)

Two other Atlas machines were built: one for British Petroleum (BP) and the University of London and one for the Atlas Computer Laboratory at Chilton near Oxford. A derivative system was built by Ferranti for Cambridge University, called the Titan , which had a different memory organisation, and ran a time-sharing operating system developed by Cambridge Computer Laboratory.

The University of Manchester's Atlas system was eventually decommissioned in 1971.

1 Technical description

1.1 Hardware

The machine had many innovative features but the key operating parameters were:

• 48-bit word size
• 24-bit address space
• 16 K words of core storeMagnetic core memory or ferrite-core memory is an early form of computer memory. It uses small magnetic ceramic rings, the cores to store information via the polarity of the magnetic field they contain. Such memory is often just called core memory or, inf (equivalent to 96 KBThe kilobyte comes in two flavours, depending on the context in which it is used, meaning either 1,000 or 1,024 bytes. The kilobyte (kB) This uses the SI prefix kilo, and simply refers to 1,000 bytes (as a kilometre equals 1,000 metres). This is the notat), featuring interleaving of odd/even addresses
• 96K words of drum storeDrum memory was an early form of computer memory that was widely used in the 1950s and into the 1960s. For many machines, a drum formed the main working memory of the machine, with data and programs being loaded on to or off of the drum using media such a (eqv. to 576 KB), split across four drums but integrated with the core store using virtual memoryVirtual memory is a computer design feature that permits software to use more memory than the computer physically possesses. In technical terms, it allows software to run in a memory address space whose size and addressing are not necessarily tied to the and pagingAlternate meanings: See paging (telecommunications). Bank switching is also sometimes referred to as paging. In computer operating systems, paging memory allocation algorithms divide computer memory into small partitions, and allocates memory using a page techniques
• Capability for the addition of (for the time) sophisticated new peripheralFor an account of the word "periphery" as it is used in biology, sociology, politics, computer hardware, and other fields, see the periphery disambiguation page. A peripheral is a type of computer hardware that is added to a host computer, in order to exps such as magnetic tapeMagnetic tape is an information storage medium consisting of a magnetisable coating on a thin plastic strip. Nearly all recording tape is of this type, whether used for video with a video cassette recorder, audio storage ( reel-to-reel tape, compact audio
• Addressing of peripherals through Vstore addresses and extracodeExtracodes were a feature of the Atlas computer. The uppermost ten bits of an Atlas machine instruction denoted which operation should be performed. If the most significant bit was set to zero, this was an ordinary machine instruction executed directly by routines

It did not use a synchronous clocking mechanism so performance measurements were not easy but as an example:

• Fixed-point register add — 1.59 microseconds
• Floating-point add, no modification — 1.61 microseconds
• Floating-point add, double modify — 2.61 microseconds
• Floating-point multiply, double modify — 4.97 microseconds