COMPUTERS AND MORE

Storage hierarchies have existed for as long as stored program computers themselves. The Ferranti Mark 1 installed at Manchester University in February 1951 had a main store made up of eight Williams Tubes each containing 32 40-bit words and a drum backing store having a capacity of 3.75 Kwords. Initially users were required to organise their own store transfers between a selected drum track and a selected pair of Williams Tubes, but the Mark 1 Autocode system introduced in 1954 carried out these tasks automatically on behalf of users and so made the two levels of storage appear to them as a one-level store. This arrangement was possible because the Mark 1 was a single user machine, and its performance was acceptable because the time required to transfer one drum track was roughly the same as the time for a programmed floating-point addition. Later developments in both architecture and technology led to the need for more sophisticated systems and a variety of techniques has been developed. These include cache stores and virtual memory.