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
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.
Emulators of Zebra included here are: