A tour of the Odra computers – computers designed and built in Poland

Odra is the name of a series of Polish computers manufactured at the Wrocław electronics plant Elwro . Subsequent generations of computers moved from valve-and-transistor solutions to digital TTL circuits. These must have been fascinating challenges: designing and establishing standards for computing machines. In theory, I would now know how to build a digital device using transistors, but I would prefer to use integrated circuits, gates, flip-flops, registers, memory or simply microcontrollers. The designers of the Odra computers had no choice but to use the components available to them.

I haven’t managed to find any circuit diagrams for the Odra series of computers; if you have any further information or spot an error in this exploration of Polish computers, please do get in touch in this thread. Better documentation is available for the Polish MERA 400 computers; I have been following the YouTube channel MERA400 , where the author demonstrates experiments with a preserved example of this computer. Another unit was located at Gdańsk University of Technology ProjektM400 .

Returning to the Odra computers, on the website aresluna we can find information on the design of subsequent Odra models and the number of units produced. For example, the Odra 1001 and 1002 were prototype models, each of which was produced as a single unit. The Odra 1002 is a valve-basedand transistor-based computing machine from 1962, operating on 36-bit words and performing 800 additions per second. The Wikipedia page on the 1002 contains a photograph showing the cabinets with the equipment installed and the control panel. This is exactly how the writers of early sci-fi films imagined computers – cabinets with lots of flashing indicators.




The computer’s design features numerous modules installed in cabinets. The modules containing vacuum tubes are connected to the drum storage heads. Perhaps the need for compact component layout, small signal amplitudes, low noise levels and specific signal frequencies meant that vacuum tubes were the better solution? Signals from the heads are routed via shielded cables; in the photograph, these are visible as bundles of red wires.




The valve modules are located in the centre. The transistor modules are on the right. The analogue voltmeters are used to monitor the supply voltages.




Transformer-based power supplies provide multiple voltages; electrolytic capacitor assemblies are also visible.




The drum memory stored 4096 words. The drive motor is visible at the bottom, as is a regulator – possibly an autotransformer. What might it have been used for? Perhaps for starting the motor or regulating its speed, although a synchronous motor should reach 3,000 rpm with only slight variations depending on the current mains frequency. There are a great many heads; I suspect that, in addition to the data heads, there may have been, for example, heads for synchronisation tracks to determine the drum’s position?




For the time being, the prototype’s design appears to be an electro-mechanical device fitted with valve modules. However, the Odra 1002 contains a large number of modules fitted with germanium transistors and diodes. Each module contains five circuit boards with semiconductors.




On Wikipedia, you can find a photograph of a single circuit board featuring the distinctive green TG2 germanium transistor and DOG-52 diodes.




A single transistor and eight diodes are visible on the board. What could this have been? Perhaps a multi-port gate? At the top there is an inductive component, either a transformer or a choke, although given the greater number of terminals, a transformer seems more likely.




The input/output devices for this computing machine were a teletype, a punch card machine and a punch card reader.
I admire the knowledge, perseverance and efficiency of the pioneers of computer science, the designers of computing machines. I wouldn’t want to build a transistor-based computer today, but the designers of the Odra 1002 had no other choice.

Surprisingly computationally efficient designs were created using transistors, e.g. KAR-65 from 1968 performed 100,000 floating-point operations per second! No wonder that the KAR-65 was used for research at CERN. The KAR-65 was designed by Jacek Karpiński , who later Between 1970 and 1973, he was involved in the construction of a 16-bit computer K-202 . The KAR-65 utilised TG-40 transistors and DOG-61 diodes; 65,000 components were housed in a modular casing typical of that period.




Digital computing machines in the pioneering days of computing must have posed a major challenge for designers; it is no wonder that experiments were carried out with analogue computers. In such analogue machines, for example Differential Equation Analyser the input and output signals corresponded to the value a, and the calculations were performed by analogue circuits. The analogue transistor computer AKAT-1 , for example, had a very interesting and futuristic appearance. A digital computer solves a problem through a sequence of operations on numbers stored, for example, in binary form, whilst an analogue computer constructs an electrical model of an equation: voltages and currents represent variables, whilst operational amplifiers, integrators, summing amplifiers and potentiometers perform mathematical operations.




We return to the eponymous series of Polish Odra computers. Following the prototypes, the Odra 1003 from 1963. It was a transistor-based machine capable of performing 500 additions per second, of which 42 units were produced. The capacity of the drum memory was increased to 8,192 words. The casing became more compact.




The circuit board layout within the module has been expanded; circuits containing 3 transistors, 6 diodes and an inductor, repeated three times, are visible.




Subsequent generations of transistor-based Odra computers became faster Odra 1013 it could add at a rate of 1,000 per second and 84 units were sold. From the 1013 model onwards, 256-word main memory was introduced, the capacity of which increased in subsequent versions. Unlike the drum, the ferrite core memory had no moving mechanical parts; access to memory cells was random (equivalent to RAM); reading a bit was destructive (the state had to be rewritten); however, unlike RAM, the memory was non-volatile.




Odra 1103 reached a speed of 5,000 additions per second and 64 units were sold. Odra 1204 that’s 60,000 additions per second and 179 units sold. Odra 1304 achieved 50,000 additions per second and 90 units were sold. The 1968 Odra 1304 was software-compatible with the British ICL1904 whilst being a faster, smaller machine that consumed less power. Designing it to be compatible with the ICL1904 instruction set allowed for port some of the software from the ICL . Elwro built a machine tailored to the existing software ecosystem, whilst improving the performance of the computer that had originally run these programmes.




Transistors occur in pairs; what do you think – are these flip-flops or gates?

A very good tabular summary of information about the Odra series can be found on the aforementioned website https://aresluna.org/attached/computerhistory/articles/odra

The new third generation of machines based on integrated circuits was launched by the Odra 1305 manufactured since 1973, the front panel of which is visible on the cover photo of this article. Odra 1305 it achieved 370,000 additions per second and 346 units were sold. It was also based on TTL integrated circuits Odra 1325 achieved 280,000 additions per second and sold 151 units. In total, over 1,000 Odra computers were produced.

From model 1305 onwards, Odra computers incorporated TTL digital circuits, which enabled a significant increase in component density compared to transistor-based designs.




On elektroda.pl, in a thread started by @djvolt1, you can find photos of Odra packages containing larger quantities of TTL integrated circuits, posted by @gizmon.


This brings our tour of the Odra series to an end; please do let us know what you think,
perhaps we can add to it, correct any errors in the description or answer some of your questions.

Those were fascinating times, the pioneering days of digital machines and computing. Old computers Second-generation (transistor-based) and third-generation (TTL integrated circuits) Odra computers look rather unusual today, a bit like the control panel of some sort of industrial automation device. Odra computers often required a three-phase power supply! It’s quite impressive to see a single transistor inside a computer. I am full of admiration for the skill and perseverance of the Polish computer designers. I suspect that the process of designing the first digital computing machines must have been difficult but also fascinating. Overcoming limitations and setting new standards must have been rewarding.

Unfortunately, we brought the design and production of computers to a close with machines based on integrated circuits. Microprocessors later emerged, and Poland was unable to maintain continuity in the design and mass production of its own large ‘Odra’-class computer systems. Looking at these pioneering designs, one can also see the enormous progress that took place in a relatively short space of time.