Olivetti P652: An intresting computer from 1973

di | 23 Novembre 2017

You might know the history of Programma 101, the first personal/desktop computer from 1965. Some people think that it was a guide in the night. But it’s not so.

Olivetti made some PC after the “Perottina”, and I think that P652 is the most interesting that makes a bridge between the old and the new PCs.

But there is a problem: A serious lack of information. If you search something about this computer you’ll find nothing.

So I’ve wrote to the Museo Tecnologicamente, a great museum in Italy, in the city of Ivrea. They’ve sent my request to the maker of the P652: Gastone Garziera.

He’s really kind and has sent me a lot of information about this computer. Maybe he can scan the general manual and put it online!

So, let’s start!


P652 uses magnetic card to store its programs and information.

Can compute floating point numbers and communicate with external devices.

Differently from Programma 101 It has 2 work register (M and A) and 240 register: 100 directly referenced (with K key) and all supports indirection (with I key). Also there was 8 index register (N) and 4 condition register.

The processor was programmed by Olivetti. In the firmware there was some mathematics functions like SIN, COS, ARC, TAN, EXP and LOG. The Olivetti’s math Angelo Barbieri wrote that functions.

Memory was measured in “position”: Both RAM and ROM had 4096 positions, but in RAM was of 4 bit, in ROM of 16 bit. ROM can host 512 instructions. Typically it hosts complex mathematics and statistics functions.


P652 language is substantially an assembly with some symbolism, heritage from the Programma 101.

Do you know the jumps in Programma 101? No? It’s not so important.

But P652 has a modern system with labels for the jumps GOTO and with a C instructions for the IF. The C make the next instruction effective if the condition is true, if not, jumps it.

GOTO supports also subroutine!

For math there is also the instruction R>P, that convert polar coordinates in rectangular coordinates and vice versa.

But a strong point of the P652 was its input/output with external drive, scientific machines and sensors. This was commanded by FMT command.

Do you have other information about this computer? Please write in the in comments!

5 pensieri su “Olivetti P652: An intresting computer from 1973

  1. John Cowley

    I had one of these at work and did some great things with it.
    I also bought a MLU600 which was the continuous tape drive thereby enabling storage of data. We had a card ledger system in our small bank so analysing data for Central Bank and internal purposes was very time consuming but with the addition of the MLU600 this saved countless hours.

    One thing the P652 didn’t have was a date function so I wrote a sub routine to calculate date values.

  2. Des Desai

    Used to be head programmer of software technical computers at Olivetti Uk in early 1970’s so know this machine. inside out The major applications I programmed used paper tape,typewriter, CT600(Cassette Tape units ) as Mag tasomething wonderful called DAS600 which was a hermetically sealed 600K Disc Driver with 50 millisecond access speeds.

    Would love to get back on one can remember a lot of the instruction set !

    Des Desai

    1. Mike Sciking Autore articolo

      This is very intresting! I think you shoul send an e-mail to the Museo Tecnologicamente with those infos, maybe they’ve go the general manual. When I was writing my High School Thesis they sent me a copy of the P602 manual.

  3. Des Desai

    The P652 was an incredibly flexible system and with the add-on peripherals very powerful. I wrote some very long programs back in the 1970’s which in essence got upgraded to a DEC PDP11/70 running RSTS/E . Even with 64K Partitions each program required 5 overlays . The sad thing was that the P652 was let down by its typewriter output.

    But for a programmer it was a dream and pretty sure that even now after 45 years I could make it sing and dance.
    240 Registers , all 15 4 bit bytes for floating point operations, 100 directly addressible. Registers could be addressed as 8 bit bytes alternatively. 8 Stack Registers with push and jump operations way ahead of the P602 . In fact, a different beast altogether in terms of power. I remember connecting a P602 to an X-Ray spectrometer analysing Concrete samples at Blue Circle Cement! The P602 had far less peripherals – the MLU600 was a 32K continuous mag tape loop hermetically sealed but with a loop time of about 8 seconds . P602 had 16 registers and I think 4 stack registers.


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