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The CTL Modular One was a computer developed in the 1960’s and 70’s in the UK by Computer Technology Ltd.

A company founded by Dr. Iann Barron. It was used by universities, some hospitals, CERN, The European Space Agency and the National Physical Laboratory (NPL) where it was used to develop packet switching networks and the first networked word processor called ‘Scrapbook’. The NPL Network had an operating speed of 1.5 Mbps which was revolutionary for the time.  Details of the history can be found on the NPL website under Mathematics and Computing (see link below).

This Modular one was purchased from NPL in 1980 together with two teletypes and a high speed paper tape reader. We are in the process of cataloguing the system components, it’s documentation and software with a view to conserving it as this may be the last one remaining. For details of the system you can download the following pdf documents;

 CTL Modular one                                     11 MB.

 System Equipment Catalogue                 31 MB.

 Software Paper Tapes                             0.4MB.

 Modular One Peripherals                        4.5MB.  

 Restoration Tasks                                  16.5 MB.

Right click the link to download (browsing may be slow).  

(All WIP and subject to change).

Links to articles related to the Modular One:


NPL Mathematics and Computing

The Scrapbook project Video

The Packet Switching project Video

Roger Scantlebury  BBC Video

University of Birmingham History

Interview with Donald Davies (referred as Modula-1 here)

CERN justification for purchase of the Modular One

Sydney Brenner, Modular One: First computer in the Lab

The National Museum of Computing NPL Internet Gallery

The Origins of SpaceWire