Stantec Zebra

Designed by Willem L. van der Poel of the Netherlands PTT in early 1950s. Manufactured by Standard Telephones and Cables Limited in South Wales. First deliveries in 1958; at least forty machines built, most of which were exported.

The machine worked serially at 128Kbs, with a 33-bit word. Main storage was an 8K word drum, with 256 tracks, rotating at 6000rpm. Internal storage was 12 single-word registers implemented as dedicated tracks on the drum, each with its own read/write pair of heads. Input was from a paper tape reader, and output to a paper tape punch and to a teleprinter. There was a control panel with a display tube, several control switches and a telephone dial for inputting small numbers. The machine consumed 7KW and had only 600 valves but rather more transistors controlling access to the store.

One reason for the small number of valves was the very ingenious but simple internal architecture. There was negligible function decoding and complex control circuits. Each bit in an instruction would operate a single serial gate directly, routing data amongst the registers, drum tracks and peripherals. An instruction had 15 of these function bits and 13 bits for store address and the remaining bits for registers and I/O. Another example of the design simplicity was that the teleprinter drive waveform was synthesised by software.

The assembler language for generating instructions was known as Normal Code, and the assembler occupied the top 1K of the drum. Casual users could use Simple Code which was similar to the EDSAC 1 instruction set, the "compiler" for which occupied another 2K on the drum. There were also a Matrix interpretive scheme and an Algol compiler.

Resurrection issue 11 has a brief article by Don Hunter about the ZEBRA and Resurrection issue 16 is a further study by van der Poel himself.

Jurjen Bos has kindly made a number of original ZEBRA-related documents available here including the original PhD thesis of Willem van der Poel!

Emulators of Zebra included here are:

64 containing an emulator by Don Hunter with advice from Willem van der Poel.

64 containing another, similar emulator by Willem van der Poel.

readme.58.txt being notes concerning zerbra58.

64 containing an Algol compiler for the Zebra.

to a web page by Jurjen Bos where you will find details of a more modern Zebra emulator which runs under Windows without any additional hosting requirement. Written in Python, full details including source code and running instructions are available.