Manchester Mark I: prototype drum

• Prototype drum for University Mark I - circa 1949. (Catalogue 2)
  
• Magnetic drum developed for the Manchester Mark I computer. Using this drum F.C. Williams, G.E. (Tommy) Thomas and others developed Manchester code, a DC-free line code that also contains an embedded clock. Manchester code was used more widely in magnetic recording until it was replaced by other line codes with higher efficiency. It is also used in digital communications where it is still in use in some simple systems such as household Infra Red remote controllers.
  
• The Magnetic Drum attached to the University of Manchester Mark I. Initially this was located in a room above the computer room. .
  
• Dai Edwards mentioned in his 1981 Digital Pioneer Computer lecture (37' 50") that at first when the drum was upstairs a program interrrupt halted the program and there was an intercom between the computer room and the drum room upstairs with transfers activated by a manual switch. Transfer directions were called 'up' to the drum and 'down' from the drum. The microphone for the intercom can be seen in SET0008.
  
• Dai Edwards also recalled he and/or Tommy Thomas coming into the University at night to help Turing operate the machine by manually initiating the drum transfers from upstairs, via the intercom.
  
• P4430J6 is the best electronic copy in this collection. The image is one of 6 scans that were made in December 2023 by Toby Howard from prints held by Christopher Anderson. Christopher is the grandson of Henry Evison, a photographer whose studio was Mayfair Studios, referred to by the initials M.S. in Ferranti records, trading as M.S. Services Ltd, 23 Old Street, Ashton-Under-Lyne, Tel. ASHton 1053. Chris recalls that he was was working at Ferranti while a student and visited the archives where he met John F. Wilson, who would have been working on his history of Ferranti at the time. Wilson gave Chris several prints of from the archives including this one -presumably images of which there were multiple copies in the archives. Wilson was not an archivist for Ferranti or ICL. Chris's prints are most likely from the Ferranti collected sales prints that are now held in the ICL collection in the Science Museum archive at Wroughton, probably from the loose prints (spare copies) in ICL collection reference 8/15/15.
  
• Dai Edwards mentioned in his 1981 Digital Pioneer Computer lecture that the first prototype drum was constructed in the Department from a cloud chamber casting found "in the debris of the physics department". Tommy Thomas recalls that F.C. Williams got the first prototype brass drum nickel plated at a motocycle component electroplating shop "across the road".
  
• Tommy Thomas wrote in his recollections that he was unable to find a photo of the first prototype, the device shown here is the one shown in Tommy's recollections and is the "beautifully machined replica built by Ferranti for the further development of the recording heads and experimentation with the magnetic surfaces". Although the drum in this photo is very dirty and it's tempting to wonder whether this might be the prototype, Thomas says "The robust base plate and gantry to support the thrust bearings (in the Ferranti prototype drum) were a joy to behold." The gantry and the base plate of this photo and others of the Ferranti drum are clearly identical and so this must be the 2nd prototype. It is likely that no photos of the first prototype drum exist.
  
• The Manchester Mark I was shut down a few months before the Ferranti Mark I was delivered. The Manchester Mark I's drum store was then used as the main memory of the transistor computer. Dick Grimsdale explained that Williams Tubes were a bit of an anathema for a transistor computer because "they had nasty high voltages and after all they were valves", and he couldn't get hold of any Williams tubes anyway so that settled it. "There happened to be a rather old drum available from the prototype Mark I" (the Manchester Mark I) and so he used that. This drum store was therefore used both for the invention and development of Manchester Code and as the main memory of the first transistor computer.
  

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This is the best of set $set205, which contains images IMG0024, P1818G-S302A, P4316J24-HJK22-26A, P4430J6 and page13d. ID: P4430J6. 9916x7396 (+TIFF) . Copyright: unknown. Collection: Scans of prints in Hilary Kahn’s original Departmental archive. Source artefact: P4430J6, 8" x 6" photographic print, condition: Fine. Artefact notes: Courtesy Christopher Anderson. On reverse: DC45. Magnetic storage drum of original Manchester University Computer, 1948-1949 First drum made by Ferranti. DC45. 2A 568.

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Set edited 2-Oct-2025 (Toby Howard)

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