Atlas: fixed store prototype

• This photo shows Dick Grimsdale working on the prototype Atlas fixed store (ROM) in the Dover Street (Zochonis) Building of Manchester University in the late 1950s.
  The Atlas fixed store was invented and prototyped by Tom Kilburn and Richard Lawrence (Dick) Grimsdale. Dick described the project in his talks to the BCS Computer Conservation Society (13th December 1994) and to the Computer History Museum (28th September 2000) in both of which he also describes his work on the transistor computer page10c.
  The store uses a two-dimensional wire mesh woven from insulated copper wire. Nodes of the mesh are locations for bits, with '0' or '1' stored by placing either a copper or ferrite rod at the correct point in the mesh. In the prototype the read wires ran vertically and the drive wires horizontally. Behind the mesh was a paxolin board covered with a layer of plastecine, the rods being pushed into the plastecine through the holes in the mesh. Every second node in the horizontal and vertical direction had to be occupied by keepers - ferrite rods that limited magnetic coupling between nearby bits, so the store only held information in a quarter of the nodes of the mesh.
  The mesh was created by Greenings a company in Warrington who made woven wire mesh, normally for filters, riddles etc. In Dick Grimsdale's talks he relates that a series of sample meshes were provided, each of which was rejected because there were points at which the vertical mesh spacing varied by too much for the store to be loaded, and possibly to function. Dick recounts in his talks that Tom Kilburn sent him to the factory to see if a single piece of mesh could be made at the required tolerance throughout, and discovered that the irregularity occurred when the operators took their tea break. They were persuaded to produce a mesh in a single session and that was used for the prototype.
  The ferrite rods were about 1mm diameter and 6mm long. Longer rods were made by Monards(?) in Blackburn by extrusion followed by a ferroxcube process. Monards(?) also had quality issues, particularly with diameter. The rod was cut to length in the department. To assemble the rods into the store a jig holding about 4x8 rods was used to insert a block at a time, this needed the mesh to be particularly regular. "2 girls" from Ferranti spent 6 weeks loading the prototype store by hand. For the production Ferranti Atlas store the process of programming was aided somewhat by "brushes" that held two rows of 17 rods at a time and that were inserted and left installed as complete brushes.
  To read or drive the store the wires were used in pairs so that the wires on both sides of the addressed rod were active, the wires were driven by transistors and terminated by impedance matching resistors to enable access times of 0.3 microseconds. The effect of the drive wires on neighbouring data was reduced by the use of keeper rows and columns with unused ferrite rods installed to focus the return flux away from neighbouring data rods.
  The prototype and the production Ferranti Atlas fixed store held 8,192 words (48 kB) arranged as sixteen 52 bit blocks (a 48 bit word plus 4 parity bits) to each row, with 512 rows.
  The fixed store was described in full in Kilburn and Grimsdale's 1960 publication, the figures in this online collection were created by Kilburn and Grimsdale for that paper, where they are reproduced:
  Kilburn, T.; Grimsdale, R.L.: 'A digital computer store with very short read time', Proceedings of the IEE - Part B: Electronic and Communication Engineering, 1960, 107, (36), p. 567-572, DOI: 10.1049/pi-b-2.1960.0170
  IET Digital Library
  
• A preprint of the paper is in the departmental archive with other copies of Tom Kilburn's papers in filing cabinet drawer D3. It is in a special IEE bound copy of four IEE papers published by the group during 1960. This preprint contains probably the best available copies of the figures describing the fixed and changeable stores.

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This is the best of set $set293, which contains images JRL220400424, P0886G-M287A and P4085J6-HJK6-3H. ID: JRL220400424. 5467x6500 (+TIFF) . Copyright: unknown. Collection: Scans of prints and negatives in the University archives. No source artefact.

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