Home Computers Behind The Iron Curtain

I was born in 1973 in Czechoslovakia. It was a small country in the middle of Europe, unfortunately on the dark side of the Iron Curtain. We had never been a part of Soviet Union (as many think), but we were so-called “Soviet Satellite”, side by side with Poland, Hungary, and East Germany.

My hobbies were electronics and – in the middle of 80s – computers. The history of computers behind the Iron Curtain is very interesting, with a lot of unusual moments. For example – communists at first called cybernetics as “bourgeois’ pseudoscience” (as well as sociology or semiotics), “used to enslave a mankind by machines”. But later on they understood the importance of computers, primarily for science and army. So in 50s the Eastern Bloc started to build its own computers, separately and “in its own way.”

The biggest problem was a lack of modern technologies. There were a lot of skilled and clever people in eastern countries, but they had a lot of problems with the elementary technical things. Manufacturing of electronics parts was divided into diverse countries of Comecon – The Council for Mutual Economic Assistance. In reality, it led to an absurd situation: You could buy the eastern copy of Z80 (made in Eastern Germany as U880D), but you couldn’t buy 74LS00 at the same time. Yes, a lot of manufacturers made it, but “it is out of stock now; try to ask next year”. So “make a computer” meant 50 percent of electronics skills and 50 percent of unofficial social network and knowledge like “I know a guy who knows a guy and his neighbor works in a factory, where they maybe have a material for PCBs” at those times.

We can talk a lot about Czechoslovak computers, for example the SAPO computer (7000 relays and 400 vacuum tubes, 1958) or Epos 2 (1968, diodes and transistors). Later on Comecon decided to build clones – better said “unlicensed pirate copies” – of western computers, namely IBM-360 or DEC PDP-11. In 1974 Comecon came with another strategy: build a line of small computers.

Just for context: at those times the CoCom embargo denied the export of modern technology to the Soviet bloc, for example modern CPUs (e.g. 68000). But eastern manufacturers made their own copies, based on reverse engineering, espionage and datasheets. Czechoslovak IC manufacturer Tesla made 8080 clone MHB8080 and copy of Intel 3000, a Germany supplier made 8008 and Z80 clones (U808D and U880D), Soviets produced 8080 and 8086 clones, Bulgarian plants made, for example, floppy disk mechanics etc.

I have to apologize to all other post-Comecon countries. They had their own home computer scenes, but I don’t know details about their computers etc. But we can say each country behind the Iron Curtain made its own home computers in 80’s. It was half on half “own design” and “clone of a western computer”. For example, Bulgarians had “Pravetz” computers, compatible with Apple II (but one type was compatible with Oric-1).

tesla1In Czechoslovakia, there was the major electronics factory named Tesla. Its name should be an abbreviation of “Technika Slaboprouda” (“Low Voltage Technology” in English), but I guess it obviously referred to [Nicola Tesla]. It was formed as a holding of diverse electronics-related plants. One Tesla made semiconductors, another one made TVs, yet another produced record player chassis. It was a little bit of competition in the world of “total cooperative” (I remember they taught us that “competition is bad” in basic school, because “workers should cooperate in developing of socialism, neither compete nor rival”).

One of Czechoslovak computer prodigies, [Eduard Smutný], together with his twin brother [Tomáš] designed the industrial computer JPR-12, based on Israeli ELBIT, and pushed it into production in Tesla. Some years later they made JPR-1, the simple 8bit computer, based on 8080. One important moment about this computer was that these designers published complete schematics and PCBs in Czechoslovak hobby magazine “Amatérské Rádio”. It was curious – you could not buy parts like LEDs in a store, but there was a very strong hobbyist’s scene. These people made radio transmitters or home automation or HiFi amplifiers. The communist regime surprisingly supported them (or better say: don’t repressed them) in their activities, because it felt the economy needed technically skilled people.

The JPR-1 was a single board computer with 8080 and its support chips (8224 and 8228) and some memory on a board. [Smutný] also designed other boards, for example alphanumeric TV display, port board, memory board, membrane keyboard, serial ports etc. Tesla made a whole line of these boards as an industrial computer, named SAPI. [Smutný] also made a Z80-based equivalent JPR-1Z, because (as he said) JPR-1 could work as CP/M machine, but Turbo Pascal needed Z80 instructions.

Tesla Ondra.
Tesla Ondra.

His last computer was “Ondra” (1986) – simple Z80-based computer with 64kB of RAM, built on single board, embedded in single case with the keyboard. Author says it was inspired by Sinclair’s ZX-81, but he couldn’t rely on ULA or similar custom VLSI, so he designed all these functions like RAM refresh or display timing as very clever hardware hacks, based on 8253 timers / counters and other parts, available in Comecon. Tesla made just about 1000 pieces of this computer, the majority of them was used in clubs of youth electronics.


Other Tesla computers were designed by Slovak engineer [Roman Kišš]. The first one, PMI-80, was a classic Single Board Computer, like e.g. well known KIM-1. PMI-80 has 8080 equivalent MHB8080, 1 kB RAM, 8255 PIO (you can add second PIO and expand the port lines), calculator keyboard (5×5 matrix) and calculator LED display (9 positions). Its monitor takes 1kB of ROM. Users can connect some hardware to control and store the programs on cassette tape (all controlled by software, no special IC). PMI-80 was widely used as a school computer or as a simple industrial computer.

The second computer, designed by [Kišš] , was PMD 85. The “85” doesn’t refer to Intel 8085. Kišš says he was inspired by Hewlett-Packard’s computer HP-85. PMD 85 has 32kB of user RAM, 16kB of video RAM, 4kB of Monitor ROM and it was based on 8080A. PMD 85 came with EPROM module with built BASIC G. G is for Graphic – and PMD 85 was the first Czechoslovak 8bit computer with fine graphic mode 288 x 256 pixels (Black and White).

PMD 85-1
PMD 85-1

PMD-85 became quite popular. It had his drawbacks; sockets for some IOs weren’t precise and some IO could sometimes overheat. On the other hand, it was really the best Czechoslovak computer of the time. Tesla made some successors, named PMD 85-2, PMD 85-2A and PMD 85-3, with better keyboard, more memory, color display or ALL RAM mode. Czech fans made a lot of games and utilities for PMD, as well as hardware add-ons, from industrial printer interface to a joystick interface. PMD still has a strong community in both Czech and Slovak Republic till today and you can buy or build for example floppy disk drive or MIF-85 – a sound interface based on SAA1099.

PMD has some clones, namely Maťo, Zbrojováček or Didaktik Alfa, manufactured not by Tesla, but by a co-op, a school supplier, or the arms manufacturer Zbrojovka Brno.

If PMD-85 was the most beloved computer, its cousin, the IQ-151 was the widely hated one. It was designed by Czech company ZPA, a research plant focused on industrial automation. IQ-151 was a very big and heavy computer. It contains “mainboard” with 8080 CPU and some support parts, dock for expansion module and the infamous power supply which overheated, but it couldn’t provide enough power for more than two modules. If you wanted to work you have to connect at least a display module and a BASIC module. It was really a horrible computer. Poorly designed, poorly manufactured, with terrible keyboard seemingly based on a doorbell. The manufacturer made some necessary changes later on, but users disliked IQ-151.

The IQ-151 was planned as a school computer and some schools actually got it. At the dawn of the Eastern Bloc, the IQ-151 was upgraded to work in a local area network, with some kind of CP/M. The Mathematics and Physics department at the Charles University in Prague developed their own operating system, AMOS, and a Pascal compiler.

Let me say a little remark about “home computers”. Ondra or PMD-85 were home computers as we understand this term now: single case with keyboard, cassette tape as storage and TV for video out. But “home” is strongly misleading in the conjunction with Czechoslovak computers. The price of these computers was really fantastic – six month average salary or so, so the majority of production was bought by schools, clubs, industrial plants or research institutes. Technically, there were home computers, but almost nobody had these computers really at home as own, personal computer.

So the question is: What did we have in our households as our real home computer? Simple answer is: Everything we could smuggle from Western Germany, Austria or Britain. The most popular brands were Sinclair and Atari. You could buy, unofficially, of course, Sinclair ZX Spectrum and Atari 800 XL at prices about one month salary. Sometimes some official importer went mad and bought 1000 pieces of Sharp MZ-821 and sold them on the local market. The same situation was with Sord m5 – there were about 1000 m5s in Czechoslovakia. At the end of 80s some Amigas or Atari STs appeared in Czechoslovakia, but again individually imported.

But none of these importers ever imported any literature, manuals, just anything, so Czechoslovak computer fans were “hackers with a reason”. Total lack of information made us find fragments of knowledge almost everywhere. In hobby magazines, bad photocopies of foreign catalogs, books, foreign magazines. My friend, for example, had only an Atari 800XL, a list of instruction names for 6502 and disassembler software, so he reconstructed the whole instruction code table and meaning of codes by trial and error. I rewrote his remarks and “discoveries” on my typewriter in three exemplars, sent them to club newsletter.

Needless to say there was not only the official electronics and radio magazine Amatérské Rádio, but some computer clubs issued their own magazines too. They were published at varying levels of quality, from four papers joined by paperclip to professional brochures, issued in series of tens or hundreds copies. Members of these clubs shared their knowledge, lent documentation and made copies of software, from cassette to cassette, free of charge. Yes, it was breaking the copyright, and it was everywhere – from hobbyists to big corporations.

The ZX Spectrum and Atari 800XL

There was two strong scenes: one around Sinclair/Spectrum, and one around Atari, both with thousands of owners. Some people had Commodore C64, some Sord, Sharp MZ or Amstrad CPC, with tens or hundreds owners of each type. But there was rare computers too. For example, my friend’s father on his business trip “to the West” bought a Laser 210, which was rare computer here. It was very expensive, so he did not buy any software or something more. My friend then had a computer with literally no software or knowledge, he had a User Manual only, and he couldn’t find anyone with the same computer to share info or software.

Talking about software – the situation was even more ridiculous! Try to guess – how many software titles for home computers could you buy in Czechoslovak software shops in 1987? No, it wasn’t 1000. Not even 500. Neither 100 nor 50… No, not 10. The correct answer is: You couldn’t buy software in a shop! There were no shops with software or computer games. It was smuggled and copied from western countries. On the other side the lack of software meant that nearly every computer owner had to learn a little bit programming, at least in BASIC. There were a lot of skilled programmers who wrote games, compilers, and database programs. Another curiosity: when you wrote a software, it was illegal to sell it! That only became legal in 1988 and you still had to get an authority agreement.

To answer to the question “why Czechoslovak home computers uses primarily cassette tapes and not floppy disks?” Because you couldn’t simply buy a floppy disk at your local shop. There were five or ten better equipped shops in the whole country and they maybe had floppy disks. They got for example ten boxes of 5.25” floppies, sold out in one hour, and no more for two, three, six months… The only solution was smuggling, or black market. It got slightly better at the end of 80s.

Didaktik Gama
Didaktik Gama

In 1987 manufacturer of school supplies Didaktik Skalica, maker of PMD clone Didaktik Alfa, made another computer named Didaktik Gama – a real clone of ZX Spectrum, extended with 8255 PIO and with RAM expanded to 80 kB. They bought a lot of original ULAs somewhere, so they built ZX Spectrum clone and started to sell it for a reasonable price. At the very end of 80’s we could buy this Czechoslovak computer at home for about one month salary.

This was the official part of Czechoslovak personal computers. We have to mention two local phenomena. The first one was a “capitalist enclave” – JZD Slušovice (JZD means ‘agricultural cooperative’). Its leader built a market oasis with a lot of economical exceptions, so they could buy ICs directly for foreign currencies, Dollars or Deutsche Marks. Therefore they made very sophisticated computers with contemporary design, for example based on Z80, with two floppy drives, RAM disk and CP/M. Oh, pardon, not CP/M, it was MIKROS or TNS-DOS – it was totally compatible with CP/M, but it was unlicensed. At the end of 80s they planned 16-bit computers compatible with PC, but then the Eastern Bloc collapsed and we could buy the original PC directly, mainly at the sales in neighbor countries like Austria or Germany.

The second phenomenon of these times was hobby computers. Mentioned earlier Amatérské Rádio published a lot of schematics and PCBs for different single board computers from Czechoslovak hobbyists. These computers had only one or very few exemplars. Amatérské Rádio itself published its own modular computer system Mikro-AR. But the most weird design I can remember was Mistrum computer – it was compatible with ZX Spectrum, but ULA was simulated by a bunch of chips from 74LSxx line. An unbelievable piece, a monument of an era in which people could develop computers, but couldn’t do it easy as “buy components and build”, the era of true hacking not for fun, but of necessity.

When the Eastern bloc fell down, we quickly filled the technological gap and started to use contemporary hardware, buy software (well… slowly) and adapt ourselves to standard computer economics (I worked with AT286 and laser printer in my first job in spring 1992). But you know – we sometimes reminisce our first computers…

Czechoslovak “home computers” from behind the Iron Curtain – or better say “Officially-made 8bit computers you could meet in 80’s”:

JPR-1 (SAPI-1):

SAPI-1Multi board computer, based on 8080A, 1kB RAM, up to 8kB EPROM. Other boards added RAM, EPROM, TV display 20 lines x 40 characters, QWERTY membrane keyboard etc. Built-in MIKRO BASIC and monitor. Its primary aim was industry.






Single board school CPU 8080A, 1.1111MHz (10MHz / 9), 1kB RAM, 1kB ROM, 25 key calculator type keyboard, 9 digit 7 segment LED display. Built-in monitor. Tape I/O. Created as didactic tool for technical schools.



PMD 85-1

PMD 85-1

CPU 8080A, 2.048MHz, 48kB RAM (later models with 56kB or 64kB), 4 kB ROM (later model with 8kB). Standard QWERTY keyboard, TV OUT 288×256 monochrome graphics, 25 lines, 48 chars. Last model can use 8 colors, first model just 4: black, white, grey and blinking). Tape deck as storage. 1bit beeper. Two parallel ports, serial port (8251). It uses ROM cartridges with BASIC (later you could buy Pascal too).





OLYMPUS DIGITAL CAMERASchool computer, based on CPU 8080A, 2MHz, 32kB RAM (up to 64), 6kB EPROM (+ cartridges), 32 lines x 32 characters TV OUT (later 64 characters per line), you can add graphic monochrome module with 512×256 pixels resolution. Single bit speaker. 5 expansion slots, two of them were permanently taken by display adapter and BASIC. Very poor power supply, tends to overheat.

Tesla Ondra:

Tesla Ondra.

Very rare computer. CPU U880D (Z80 clone from GDR), 2MHz, 64kB RAM, 4kB ROM, TV display 20 lines x 40 chars, graphic mode 320 x 240 monochrome. QWERTY keyboard, tape interface. BASIC was on the tape and you had to load it before use.


Didaktik Gama:

Didaktik_GamaZX Spectrum clone with original ULA (later models Didaktik M and Didaktik Kompakt from early 90’s use ULA1 from USSR, so the display was square shaped instead of rectangle and there were some timing incompatibilities). It was the first real home computer you could buy.


About the author

EK35_Maly3_Ren_Volf_k[Martin Malý] works as a media technology consultant and team leader of developers for some Czech newspapers. He has experience from startups and did a lot of web projects (e.g. was a Lead developer, Programmer, Administrator, Manager and Ideologist for a cutting edge Czech blogging system called Bloguje.cz).

His biggest hobby, beside programming, is microelectronics and old computers. He did some task programming on railroad engines, based on microcontrollers (8051 family, AVR, Microchip) and some “homebrew” gadgets, computers etc. He joined his two hobbies together in ASM80.com – an online IDE and assembler for 8bit CPUs.

[Martin] is an Evangelist and Teacher of New Web Technologies (OpenID, OAuth, cloud computing, HTML5, Node.js, Coffeescript and other stuff) as well as Evangelist of HTML5 development for mobile devices.

He does quite a bit of writing – starting with some juvenile textperiments, continuing through a series of blogs and online magazines, and he ended up as an Editor-in-Chief of zdrojak.cz – an online mag about web technologies.

121 thoughts on “Home Computers Behind The Iron Curtain

  1. I remember in the late 70s there were controversies about selling supercomputers to the Soviets. The concern was they’d use them for nuclear weapon development. We (the public) were assured that the computers had been modified so they could only be used for things like weather forecasting.

    Now, we all walk around with far more powerful computers in our pockets, and none of us use them for developing nuclear weapons. What the heck’s wrong with us?

    1. The embargo harmed the world. The SKALA computer that was in the Chernobyl power plant was much slower than it could be, as it was Russian tech. It took over 10 minutes to process the core reactivity. When the reactor became unstable, and changing too fast, it was too slow to tell the operators that continuing is not a good idea.

      Embargos kill and should never be respected.

      1. I’m not crazy about embargoes either, but there was a lot wrong at Chernobyl – and in the entire Soviet bloc – that had causes far beyond the embargo (e.g. sociopathic rulers and bureaucrats who cared more about their power than their people). I don’t think you can blame the embargo for Chernobyl.

          1. ,,-~*~,,

        1. Embargo yes, but not material.
          Crucial technical details of the RBMK-1000 were classified (to prevent those pesky capitalists from building cheap, yet at that time very big reactors :D ), so while the operators had instructions what they were supposed to or absolutely not supposed to do, they didn’t know as to why and what the consequences would be (other then going to jail for breaking the reactor :P).
          Had they known, I’m quite sure the operators would beat the living shit out of the test director present that day (he was responsible for several of the bad decisions in quick succession that caused the runaway) when he would’ve demanded what he did on that fatal night.
          None of the other RBMK-1000 that have been built had any severe problems, despite the material shortages, embargoes and not so well thought-out design.

          1. The Leningrad plant actually had quite serious problem of the nature similar to Chernobyl, some years before, but there was only a localized meltdown. The secrecy policies deprived the Chernobyl staff of this crucial knowledge.

            There was another little-known embargo/trade-related issue; a mobile vibration laboratory bought from Switzerland a year before by the Charkov turbine plant, present at the site for the second test that the English literature rarely mentions. Rare, bought for tight-supply foreign currency, and maybe somewhat unofficially (from the west side) obtained; tech smuggling or at least rules-skirting was happening a lot. So the other test was vibration-measurements on the turbogenerator 8, specifically the bearing #12, which had chronic vibrations-related issues. For this, the thing had to be put through a range of rpms, for which slowing down during the shutdown was ideal. My hypothesis is that the dearth of the measuring equipment of this class (the lab was a car full of dataloggers and computers) greatly contributed to the urgency of doing the test that day. Without these measurements, the problem of turbogenerator 8 would go unresolved and 500 megawatts of power could go unpredictably offline anytime.

            Popov and Savenkov from the Turboatom plant, from the mobile vibrolab, died due to the accident, partly due to exploring what did happen, partly due to attempts to save the car buried in radioactive debris.

            More details are available in Russian, using the names of the casualties and companies as keywords.

        2. Yes, maybe if the fat idiots running the Soviet Union, and skimming off of the top all of the time, would have put more resources into their safety engineering THAT would have prevented the disaster they created. Or, maybe if their system rewarded competent engineers, programmers, etc, rather than just political flunkies, people would have been more motivated and worked on better technology. I am always impressed at what Soviet technical people accomplished with what they had- very clever,rugged, and simple usually, but 30 or 40 years behind.

          1. REVISIT:
            Yes, maybe if the fat idiots running the WEST, and skimming off of the top all of the time, could have put more resources into their COMMUNITIES

          2. We are talking about Chernobyl, so what is your point? I am responding to a comment blaming the disaster on the embargo, rather than the people responsible. I did not say western leaders are not usually idiots as well, however it is amazing how super educated people in the Soviet Union and “block” countries would have very little benefit for all of their efforts. I would not trust bridges built by engineers paid $20,000 a year, or want to go see doctors who make less than your average workers. So again, your comment has nothing to do with preventing Chernobyl.

      2. “The main process computer, SKALA, was running in such a way that the main control computer could not shut down the reactor or even reduce power” ~ “All control was transferred from the process computer to the human operators” – source Wikipedia

        So your saying that an embargo contributed to a disaster in which the computer was turned off or set so it could not do its job?

        1. The computer could not deliver its advice to the operators in time. Its advisory-only role is logical, as it was too slow for realtime control. Its slowness, both in the technical infeasibility of directly controlling the reactor, and in delivering the crucial information too late (or, not delivering it at all as it got flooded with the coolant water in the mishap), was what contributed to the event.

      3. Was it because the hardware was too slow, or could the code have been better written to be faster on the same hardware? In my experience, you can always come up with better ways of coding so that the code runs faster, and the only reason that this doesn’t happen is “it’s fast enough, I’m going to stop working on it now”. A lot of that comes from people being spoiled by machines with virtually infinite RAM, and faster clock rates than they need to do the job right in front of them.

        If core reactivity processing latency was a critical failure path, then that should have been considered in the design. Blaming the technology they picked to do the job, for some engineer not doing the right thing in the design.

        BTW, you can effectively do this in RT with an 8 bit microcontroller by periodically calculating ρm(IRPN-Ϝ0)=f(IRPN), maintaining a weighted moving average for the result, thus giving you the slope of ρ. So blame the stupid engineer, and blame the technician, don’t blame the computer being slow.

        1. There are absolutely theoretical limits to the efficiency of an algorithm, as I’m sure you know. Chernobyl blew up in 1986, but it was built in 1977. Even if the lag in technology behind the US was only a year or two, that’s still mid-70s tech. I don’t think complacence over “virtually infinite RAM” was a significant factor, and this is ignoring the fact that processor time and amount of memory aren’t the only parameters of performance. Even if the code was terribly written, that’s still primitive enough hardware that there’s a very good chance that even a theoretically ideal algorithm would have still had issues.

          And even *this* is ignoring the fact that the workers disabled all safeties–not just the supervisory computer–and then responded in exactly the wrong way when things started to go tits-up. The slow computer, quite frankly, would not have been able to save them.

          1. I think you meant to say “even a faster computer…”.

            If I were a tech, and it was my job to watch a dial and react to a problem, and every time I did, 10 minutes later, an ear-splitting alarm went off, I might think about disabling the thing too, since all it would mean was “you would have been dead by now, if you hadn’t been watching the dial”. Latency might have been a factor init being disabled.

            On the other hand, the processor on the SKALA (which was a V-3M, which was the industrialized version of the M4-3M Control Computer) was capable of 400K IOPS/second, which if given 5% of the CPU, with the rest going to PRIZM and other processes designed to actually raise the alarm, had they used the algorithm I suggested (above) could have sounded the alarm in about 43 seconds. Just saying.


            I wonder if anyone has enough data on the thing to build a simulator? :)

            PS: I heard they read the audit tape out at the Smolensk reactor on the same type of computer because that’s the control computer there, too, which is one of the major ways they knew the accident timeline, so I’m guessing they don’t have enough data on the hardware to make a simulator.

      4. Too bad. We still have not learned to stop feeding our enemies- as evidenced by Russian behavior currently. Pretty big stretch to blame such a huge Soviet screw-up on anyone else. Poor design, hiding mistakes, idiots in charge, no resources or training to deal with accidents, “need to know” that is more political than the actual people running the reactor NEED TO KNOW…..

    2. There was no controversy: we didn’t allow it to happen. I know some of the people who took the VAX 11/785 (first SMP system) out of it’s crate, filled the crate with quick setting cement, and then let the Russians pay the shipping costs on it as it was shipped to the imaginary front company in Basil, Switzerland, which was responsible for smuggling it into Russia to be reverse engineered.

      And yes, it would have been used for nuclear research; disclosed Russian documents after the fall of the Soviet Union verify this.

      1. I think it was a foregone conclusion given how the Cold War developed. When the size and effectiveness of your nuclear arsenal is the primary deterrence against a potentially apocalyptic war, you keep your arsenal up to date. It’s the only sane thing to do. This is on top of the Soviets having a disadvantage in terms of the accuracy of their delivery systems (and knowing it.)

  2. I should still have the IQ-151 somewhere. Bought it cheap for salvaging the power supply, and procrastinated until it became a relic. The keyboard was atrocious.

    Also remembering a PP-06, a PC-XT clone (Bulgarian, perhaps?) that was fairly common here in 80’s. Two 5.25″ floppy disks, one for OS, one for data. Could be extended with a hard drive, a MFM one with a separate controller card. The power supply was pretty good, built to last – I know about application where the original computer is gutted, replaced with a PC AT motherboard, and runs on the original power supply nonstop for over 15 years.

    Common imported computers were Sinclair ZX Spectrum, Atari 800, and Commodore 64.

      1. Actually we had two producers of computers in Bulgaria. One was the factory in Pravetz which produced things like Pravetz 82 (clone of Apple ][), Pravetz 8A (“enhanced” clone of Apple IIa), Pravetz 8C (“enhanced” clone of Apple IIc with Bulgarian-made CMOS version of 6502 – CM630), Pravetz 8D (clone of Oric-1), Pravetz 8E (1:1 clone of Apple IIe, produced in Taiwan and imported in a very limited quantity in BG around 1985), Pravetz 8M (dual-CPU: besides the regular 6502 it has a built-in language card in the form of a soldered on-board Z80, which has no direct Apple counterpart), Pravetz 8S (improved version of 8C with up to 1 MB of RAM and reprogrammable keyboard), Pravetz 16 (IBM PC/XT), and Pravetz 16 E/ES (improved PC/XT with NEC V20 CPU).

        On the other side was the IZOT consortium that produced modular workstations and industrial computers like IZOT 1031C (U880D powered) and IZOT 1036C (16-bit, PC-compatbile, better known under its EC identification as EC-1832).

        There were also two set of schematics for modular computers available. One could be found in a set of 12 books on computer technology. Volume 12 “Build yourself a computer” gives a detailed explanation of the design and functioning of one bus type and provides schematics for CPU modules (both 8-bit and 16-bit), memory, and IO modules for that bus. The other one was published in the Bulgarian amateur radio journal. I am not aware of anyone who has ever built a device based on those schematics.

    1. PP-06 was a Czechoslovakian machine – a 4MHz PC-XT clone, commonly found in schools along with a “network” of Didaktik Betas (improved PMD-85 version in a different case).

      I have used a few of them back in the day – the machine was very slow even for its day and horribly unreliable – crashes, freezes and various malfunctions were common. However, that was true for most of those machines – lots of engineering shortcuts had to be taken because of components not being available, so you had power supplies there were literally melting, marginal bus designs where all it took to reset the machine (and lose all your work) was a bit of static discharge, etc.

      There is a good page about these machines here:

      1. I had one PP-06 at home later in 1990s (it was disposed unit from an university).
        It had 640K RAM which took minutes to check during POST and a harddrive. There was only a single 5 1/4 floppy drive for 360K floppies and a Phillips monochrome monitor.

        It was rather slow, not fast enough to run Prince of Persia at normal speed (you moved in a slown-down fashion). I didn’t experience much instability from it, although we would turn it off or reboot often because we hardly understood DOS and how various programs work, so often we didn’t know how to get back from something. We used Volkov Commander (clone of NC) to operate that thing mainly.

    2. IQ-151 had several “great” features – the keyboard, that after some use required sharp and violent jabs to actually press the keys. Also its TV out signal was powerful enough that you did not really need the TV to be connected to the computer. I was once summoned to help younger schoolmates with misbehaving computer, that seemingly ignored user input and typed programs on its own. When I checked, it was not a case of AI, but the case of victim’s computer being turned off and the TV tuning to signal from his neighbor.

    3. The photo of the IQ-151 reminds me of a joke about French engineering, They tried to copy the looks and guessed at what they couldn’t see. The case is reminiscent of an Apple II, the keyboard looks as if it was salvaged from an old Olivetti calculator and it houses an 8080 mainboard…

  3. I’m not old enough to have experienced it, but in the 1980s in Yugoslavia the student FM radio station broadcast pirated videogames for the ZX Spectrum during the early morning hours.

    1. I’ve got a better one. Here in Romania, the state-owned television TVR1 used to have an 1-hour show in which, yes, they did broadcast spectrum software. Guess what was the first program they broadcasted ? Copy86M, a program for copying other software.

      1. This happened after 1989 for sure. I think the show was presented by Alexandru Mironov, who acted as the ministry of science and technology during the first government in 1990. In no way the TVR broadcasted such things during Ceausescu’s times. I recorded some of the software broadcasted on a Grundig tape recorder and actually used it on a HC85 and Cobra.

  4. PMD-85 2 and later got worse keyboard then PMD-85 1. First got classic tact microswitches. But the later versions got golden galvanized PCB with conductive rubber switches which was very inaccurate made and usualy got stuck after five push.

  5. That must be the best article about life behind the iron curtain I ever seen.

    We lived paralell lifes on different sides of the man made wall, but in large we did the same things with the options we had at hand, and even after the fall of the iron curtain, the people from the eastern block often was the better programmers, since they had to run their programs on a one-slot-toaster and not on the latest hardware.

    I’m also a ham-radio operator, and would love to read about that scene too, but wery little seems to be written since most people dont think that it is something to be proud of.

    I truly admire the people doing big things with small resources, and working around obstacles that we couldnt imagine.

    Please, please, please, write more about it!

        1. You can check out the archive at http://www.diagram.com.ua/english/library/amaterske-radio-magazine/ . It’s in Czech, but I think you can see enough from pictures and schematics. From today’s perspective it’s interesting that apart of the ham radio equipment (transceivers, antennas, even home-made RTTYs), most of the constructions published was home-made lab equipment like multimeters, frequency counters, oscilloscopes or power supplies. In that times, these were either impossible to obtain, or prohibitively expensive. Just getting one’s hands on an ICL 7106 and an LCD display so one could build a digital multimeter was quite a feat.

  6. Fascinating article, and a very interesting look at the technological history of a time and place that is seldom heard in the Western Hemisphere. It just goes to show that hacking is a somewhat universal response to certain needs and wants.

  7. It needs to be said that apart from the Didaktik Gama/M/Kompakt, the remaining machines were not really intended as “home” computers. In fact, they were only sold to “socialist enterprises” (hard to translate expression) – basically schools, free time centers, research institutions or (state owned) companies, not in retail.

    That is especially true about the Didaktik Alpha/Beta series – those were literally meant as school or educational machines (Didaktik was a company producing school supplies and equipment) and only very few have ended up in private hands.

    There have been quite a few more machines not mentioned in the article – PP-01/03, PP-06 (IBM PC/XT clone), Didaktik M (fully compatible ZX Spectrum 48 clone), Didaktik Kompakt (same as M, but with a built-in floppy), the whole SMEP minicomputer series (PDP-11 and early VAX clones), JSEP system (Comecon-wide effort for development of compatible mainframe series derived from/inspired by IBM 360 series), etc.

    There is some info here:
    http://www.homecomputer.de/pages/easteurope_cz.html (microcomputers)

    SMEP (minicomputers)

    JSEP (mainframes or what used to be called simply “computers”)

  8. Great article, thanks!

    I remember my colleague recording his program to the casette tape recorder of PMI-80, singing vaious enchants to make it record correctly (the tape recordings were a bit error-prone). A week after when he want to retrieve his program, all we can hear from the tape recorder was his singing enchants – he forgot to connect the tape recorder with PMI-80, and all it recorded was through the internal microphone instead.

    We made fun of him for several years after :-)

    1. :-) my very first assembly code was on this little beast! there was government org “SVAZARM” (something like “civic to army cooperation union”) where we as kids was on summer camp; together with more experienced older friend we coded melody playing routine, but due to bad pointer bug at first run, it took monitor rom as data and PMI produced some very random “music from mars” :-D quite great times despite red-alert around…

  9. Interesting article…but for the love of transistor radios man, what is it with hackaday forgetting to put things behind a fold to make for a more compact site?

    Posting this small novel without a fold is a horrible idea guys.

      1. Fine, thank you. Also, the one instance of “dawn” in the text should have read “dusk”. Locals surely understand when exactly was it that AMOS appeared but foreigners would be confused by that.

          1. I’m not sure what you don’t understand about that. The command economy’s motto was “competition [note: ‘konkurence’ in Czech] is bad”, not “concurrency is bad”, and AMOS and IQ-151 networking were designed at the end of the 1980s, which was the dusk of the Eastern Bloc, NOT its dawn. There was no IQ-151 at the dawn of the Eastern Bloc. Only SAPO. :-D

    1. Yeah, Martin’s English is not at a very high standard .. But please remember that he couldn’t start learning English back in elementary school like it is the case nowadays. Not all of us – Czech people – only speak Czenglish ;)

  10. Marvelous article! Thank you! Have been always interested in parallel development of certain technologies that didn’t cross path (e.g. this, and the mobile computing culture in Japan in the 90s when not many had a computer but nearly everybody had a data service enabled cell phone.)

    1. Many families had their members and friends in western countries because they left mainly after 1948 (beginning of communist era in the Czechoslovakia) and after 1968 (Soviet invasion). These people sent western goods to us. And a smuggling too. Sorry for my English.

      1. And don’t forget “Tuzex” network of shops that sold in the Czech Republic Western goods (applied with special currency – the Bon). In this way it was possible to buy, for example, Atari, Spectrum, Sharp… The problem was the Bons get .

  11. In interesting but lengthy article, going to have return to read in smaller bites. Interesting how amateur radio was seen as worthy of supporting, but not lobbyist computers. A much simpler task to monitor radio transmissions I suppose.
    A lot of lip service is paid to how competition is good here in the SA the reality is, but policy is tilted towards those who have already made it. Abe Lincoln would be called a Marxist by many in the US because, recognizing the value of businesses businesses he also noted there is no capital without labor. Thanks for putting forth the effort Martin.

    1. The difference was that amateur radio did not need western components, unlike computers. And even when the western parts were replaced, they were manufactured in small amounts only.

      On the other hand, transceiver could be built from common parts produced (and sold!) in comparatively big amounts for use with TVs and radios.

    2. Amateur radio schooled people to be good military signalists, and was probably supported for that reason.

      Just as glider-flying in germany between the wars schooled the next generation of military pilots..

      If it’s good for the military, it is good for the country.

      1. >Amateur radio schooled people to be good military signalists, and was probably supported for that reason.

        big fat NO. Government was constantly after HAMs in Poland. At the same time HAMs caused all sorts of problems, from broadcasting pirate radio, to hijacking TV station signal and overlaying subversive messages.

        note the SOLIDARNOSC banner overlayed over official news broadcast

  12. Talking about computers is not complete without mentioning printers – in hobbyist setting it meant either some strange tape recorder/single dot printer combo we had with Zbrojovacek computer, or building your own from the Merkur toy set.

  13. He he, that is great. I grew up in East Germany and our KC85-3 (KC stands for small computer in German) looked JUST like the PMD85 from your pictures. Guess we did all copy from each other as well as from the West.

    I learned programming on the KC85-3 when I was 8, and it’s been a wonderful journey since :)

  14. As someone who grew up in the same spacetime, I would like to add one interesting fact. Despite there were relatively few computers among people, starting mid 80’s the Saturday morning youth programme “Pioneer Swallow” broadcasted lessons on programming – on official TV channel! If I remember correctly, at first it was in the Karel language (pretty sound introduction into structured programming, even today), but later on the main focus was on Logo (~vector graphic programming ;-)). I vividly remember scores of schoolchildren impatiently waiting for their limited time in computer classroom, many of us “programming” on squared paper.

  15. It wasn’t just the countries behind the iron curtain. As a kid growing up in India in the 1970’s and 1980’s we faced the same problem. You could not just go out and buy a home computer. They were either smuggled from Hong Kong or Singapore, or brought in by your uncle or brother who had managed to find work overseas after paying a huge import duty and bribes to customs officials, often greater than the cost of the computer itself.

    Popular computer and electronics magazines never made it to India. We had our own local electronics magazines and homebrew clubs but not as successful as those in Czechoslovakia. Things were very expensive due to the value of the Indian currency, the Rupee, and the conversion rate against the dollar. This limited what we could buy and do. In a way this was a push towards making things cheaper and finding alternate ways of doing the task.

    My first home computer was the Laser 200 which one of my cousins brought in from Hong Kong. It came with the 16K RAM expansion module and a couple of games. The games were loaded from cassette tape. For the first couple of months I had no access to a tape player, and had to wait till one of my uncles brought in an old Panasonic portable mono tape player from Singapore.

    At the time, there was a severe lack of information and teaching in this domain. A few of us got together to create a small training program to teach others to program in Basic on the Laser 200. It was a roaring success, even though the 12 people in the class had to queue for access to the Laser 200 to try out their code. It also taught us discipline in design and coding, like the old mainframe batch process days. I even used a typewriter to create “completion certificates” for all 12 of our “students” since we had no access to printers.

    In 1988 I managed to obtain a Sinclair ZX spectrum 128K through one of the “not so legal” channels in Bombay for a price greater than my father’s monthly salary. We also had access to a BBC Micro with the 6502 processor in school. That was an amazing little piece of engineering for the time, which allowed us to write assembly code inline and work on performance optimisations in the graphics that we simply could not achieve with Basic.

    Software was still passed around as copies on cassette tape. Making copies was a challenge in itself. Early on, it was very low tech – we connected two cassette players together and made direct audio copies. Of course, this would result in many corrupted tapes. Later, there was a program called “duplicator” which would load the entire contents of the first tape into the computer’s memory and write it out to tape. This greatly increased the success rate of our copies.

    The computer science department in our school had an old huge beast of a computer running CP/M. Most of us had to queue to validate our programs on that monster. Later, the school got a Kaypro-II also on CP/M. The next year, the school budget was increased to allow us to buy two IBM-compatible PC’s running 8088’s at 2 MHz. These computers had CGA displays with green phosphor monitors. That was our first taste of the concept of an operating system (MS-DOS 3), floppy drives and so on.

    Interesting days, but not something I can envision going through again just because of backward political and economic thinking in our country.

    1. Curious and sounds disturbingly familiar. Back in those days Soviet Union used to buy certain computer components, usually dot-matrix Epson printers, via Indian resellers to circumvent the embargo. It was typical to have “RAVI” branded printers, but you could just remove the sticker to reveal the original Epson logo. The prices were outlandish for home users, but they went to schools and various institutions.

    1. In fact, this was happening sometimes :) The big iron stuff, the EC1027 (?), basically a clone of System/360, had a ‘localized’ OS, thus the most common messages were displayed in Czech language. The not-so-common ones came out in Russian, and when you got really lucky and got into some sort of unusual problem, you got the original English message displayed :)

  16. The IQ 151 used to get so hot, that if you were to put a cup of coffee on the top of it, it would stay worm .. good times :) Also, the ICs that weren’t soldered to the board would pop up from the sockets, it was extremely annoying

  17. Just a minor update. Another nice school computer was TNS HC-8, with Z80 clone, CPM-like OS (TNS-DOS mentioned above), something like 256kB RAM (part of it used as RAMdisk), typically booting over sort of a network from central computer. This thing was pretty usable, got a decent keyboard, and even two apple / cup holders :) (some models had acoustically coupled modem, the case was shared for all models).
    I really enoyed programming it. http://www.homecomputer.de/images/infos/east-europe/TNS_HC_08.jpg

    1. Just found some more details. 3MHz Z80 clone, 320kB RAM, SIO/PIO/CTC clones, 2×8255 for I/O. 4kB EPROM for loader, RAM was paged or used as RAM disk. Mouse interface, modem, two 20mA current loops, floppy controller for two drivers, 100kBd local network over two BNC connectors (the network was some kind of a ring topology, and it was extremely slow when all ten computers on the network were bootloarding)
      32kB shared RAM used for video. Supported serial and parallel printers. Keyboard fully passive, matrix 8×16, 111 keys.
      Text mode 64×21 (characters had 8×12 pixels). Graphic mode 512×256, 16 colors (in two modes).
      Power consumption 20W.
      The FDC was optional, and I bet a lot of the other peripherals too – I never saw HC-8 with FDC.
      Friend of mine did a lot of hacking, and he even managed to connect to my PC somehow (he wrote an FTP client or something, over serial line).

  18. Its true, Russian and Bulgarian computers use the Cyrillic keyboard while most other eastern block states must have adopted the roman alphabet ages ago with subtle unique differences such as special characters much like the Vietnamese roman alphabet

  19. ya, once upon a time :-) … back in 1988 at “control systems electronics” high school in Kutna Hora (also really nice historic UNESCO-listed mining town with famous known gothic cathedral) I used wonderful german ATMAS-II macroassembler to write 8080 emulator (as fast as possible) for 6502 (Atari 800XL) – primarily for “home education on INTEL cpus” to “match” the real home computers (6502 based) to our own czech expensive and unreliable “home” computers existing only in schools really – so sorry mr. Hofacker … there was nobody to whom to pay licence fee for your loved ATMAS :-( There was simply everything stolen and copied massivelly, but I strongly believe that it all also helped to “break the wall” too :-)
    Cheers! falken

  20. Excellent article.

    Besides living on the other side of the iron curtain at that time, I’m in a country that had some (but not so harsh) conditions you described (Brazil) – so I understand pretty well what you talk about: we had our share of interesting computers also. :-)

    Thanks for sharing your memories.

  21. Don’t forget that personal computers were horrendously expensive in the west in the late 70’s-early 80’s. So even though they were available, they were about 3 or 4 months of pay. It was only when the VIC-20 and the like became available that home computers took off. You still needed a TV monitor and cassette recorder to make them work.

    1. I can’t speak for wherever you’re from, but in the US only the latest-and-greatest was extremely expensive. Apple computers were outrageously expensive, but other manufacturers made at least one line of their systems affordable. For example, while the original TI 99/4 had been approx $1,800 in 1979, only a year later they released the 99/4A (which had a ton of improvements, like lower-case text) for only $525; the original Commodore 64 was $400, but the much fancier Amiga that came out after it was $1,200.

      Also, don’t forget that at the time, the cost of food, housing, and medical care was a *much* tinier percentage of a person’s total income than it is today. So while the average income for a median household was $17,000 (and minimum wage $3.30/hr) a large chunk of it was disposable for the middle class. It was normal for a family with two kids & stay-at-home parent to buy a nice 3-bedroom suburban home and live quite comfortably on the other parent’s income as a postal worker, teacher, janitor, or other job with unimpressive pay. That made a huge difference, too. :-)

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