Stantec ZEBRA

The Standard Telephones and Cables Limited (Stantec) ZEBRA was a designed by WL van der Poel in the Dr Neher Laboratory of the Netherlands PTT. He was responsible for the name, coming from the Dutch ‘Zeer Eenvoudige Binaire Reken-Automat,’ meaning ‘Very Easy Binary Calculating Machine’. The hardware was designed in Newport and around forty were produced in total.

The original version used 600 thermionic valves, but relied on transistors for store switching. The machine used printed circuits for internal wiring. This was a very new technique, with the first patent having only been filed in 1950 and issued in 1956 - two years before the first ZEBRA shipped. Many competing systems used more ad-hoc wiring, which made tracing faults more difficult.

The Zebra used a magnetic drum, capable of storing 8,192 words and with a maximum seek time of 10ms. It is interesting to note that 50 years later, a typical hard disk has around sixteen million times that storage capacity, but very similar seek times, rarely lower than 5ms. Hard disks are the direct descendant of magnetic drums - simply moving the magnetic substrate to the surface of a disc rather than a cylinder. This technology has lasted over five decades as the main long-term storage mechanism for electronic computers and, while it is increasingly being replaced by solid state systems, is likely to be around for a few more years.

Complex Instructions

Each instruction in the ZEBRA was a combination of simple mathematical operations. Operation codes were 15-bits long, with each bit representing a single operation. Any of these 15 operations (add, shift, and so on) could be combined into a single operation.

While incredibly flexible, this scheme was complicated to use, and an additional mode known as simple code was provided. In his reminiscences, Rod Delamere explains that ‘The Simple Code programming language was anything but’.

David Chisnall

Further Reading: Rod Delamere’s reminiscences on the Stantec ZEBRA at Newport in 1961; 1958 Brochure; 1961 Brochure