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WEBSITE LAST UPDATED: 2024-Aug-16

This site is dedicated to a page of computer history, dating back to 1985-1996, in a part of the world known as Romania. By the effort of a few people there, a new breed of Spectrum 48 compatible arose, designed by engineers, manufactured by a few communist factories back then and unofficially improved by students in campuses of faculties in the capital of the country. The name of this computer is ...



Original logo (1986)

Anniversary logo (2016)


CoBra computer from the 90's, in original case

CoBra computer built in 2016, custom case


Before anything, I want to clarify the origin of this name: "CoBra" stands for COmputer BRAsov. and Brasov is the name of a city in Romania where in 1985 a team of 8 researchers including eng. Vasile Prodan was assigned the task to design and build this computer. I do not claim any credits for anything described on this website. The purpose of this website is to preserve this project which otherwise would be lost.

In 1990 I was a student and just like many others I had found out about this new "toy" called computer which was being built by students in private in campuses in Bucharest. I started my student years in 1988 in Timisoara, a city in the west of the country. There wasn't much going on in that city, and when I got word from friends that in Bucharest students were building computers in campuses I decided to move from Timisoara to Bucharest, which was a lot closer to home too.

In Bucharest there was quite some traffic with parts - integrated circuits, printed circuit boards, keyboard components (individual keys + circuit boards for keyboards). If you went to the right place and to the right people, you could buy all the needed parts to build this computer by yourself. All you needed was the knowledge, and that's where the hard part was.

Assuming you had the schematics, you were only the first step up the ladder in the quest for building the "toy". Back then you could find the "official" manuals for it, including the hardware manual which had the schematics and the functional description. But the very hard part was that both the manual and the original printed circuit board being manufactured had a lot of errors. Some errors were detectable by reading the manual and comparing the schematics in it with the circuit board. This was quite a slow process if you did not have anybody to tell you where to look. Other errors were in the very schematics in the manual, and those were impossible to track down without somebody to tell you what and where. Usually, if you did not have the right friends you would end up paying for information.

Other errors (and this is the most rabid part...) were simply fabrication "defects" in the printed circuit board which back then I suspected were quality control rejects being smuggled by money makers. This was just my impression. The truth may be what you can read on the "History" page, and that is there was quite some rivalry going on between different Spectrum clone manufacturers in the country at that time. The situation was that in Romania the personal computer was just being born in that period of time (the late 80's). Every major university centre in the country (Bucuresti, Brasov, Cluj, Timisoara) had a team of talented people who would come up with their own design of a Spectrum clone. Usually they were also manufacturing their computer in the same city. This computer (CoBra) did not have its own independent production line. Its designers were based in Brasov, but the printed circuit boards were being manufactured at a factory (FCE) in the capital of the country, Bucharest, which factory was also manufacturing their own Spectrum clone, named "HC" (stands for "Home Computer"). They made several models, like HC85, HC88, HC90, HC2000. They did not want CoBra to have much success, so they sabotaged it every way they could. They "slipped" a lot of errors on the printed circuit boards and they manufactured them at a very poor quality. The design of CoBra was much superior to the HC's so the inevitabile envy and hate for it was quite fruitfully manifested. You can read more about this on the Floppy Interface page.

Anyway, around 1990-1992 I managed to build 2 working CoBra computers using all the information I could gather. I had my own hand-written schematics copied from some photocopy of the original manual and some additional schematics given to me by a couple of friends. As I was going along, I was finding out about "modifications" they were making to the original schematics in order to get improvements or extra features.

After getting the college years done and starting a job and dealing with life, all this universe of the CoBra computer started to slowly fade away. At the end of 2009 though, I was again in the position to have spare time for my own projects. So I took all the documentation I had about the CoBra computer (schematics, manuals, the actual circuit boards) and I started studying the whole thing in order to restore the project from the dead, this time in an orderly, up-to-date computerized fashion.

This website presents all the documentation and other information that I have, related to this computer, including, first of all, the documentation for the original project, then all the improvements I have ever made and used for it, software as well as comments on functional details. All information presented here is to be considered Open Source. Anyone is welcome to use it and replicate any version of this computer presented here, even for a profit. All information necessary for a full replication is presented, including drill maps and Gerber files for all circuit boards. Also any comment or suggestion is welcome, for now you can contact me by posting a message in the RomanianHomeComputer forum on Yahoo (email address RomanianHomeComputer@yahoogroups.com) with the subject: "CoBra Back to Life". I know there are a few people out there (outside Romania) who would like to know more about Spectrum clones built in Romania. For them I built this website in two languages, one of them being English. This way anybody can take a peek at this particular page of history called "CoBra". There weren't many good things born in that country, but this is definitely one of them.

My approach will be to try and build and then test every single circuit I present on this website just to make sure it actually works. I will make a note every time whether or not a particular schematic or version has been built and tested by me.

The original project, as described in the original hardware manual, had a total of 64KB RAM and used 4 banks of DRAM, each one having 8 DRAM 16Kx8bit chips. My plan is to draw up revisions to this ORIGINAL project, WHICH I will name "Version 0". The goal is to build a version (or more) to the original project which would use up-to-date available components (within today's possibilities, since 8272 has been out of production for quite some time and is too complex to be replaced with anything else still in production).

* * *

Now, for those who never heard of this computer (but still know what a Spectrum 48 is...) I will make a short presentation:

The original version of CoBra had 64KB DRAM split in 4 banks of 16KB (eight 16Kx1 chips per bank). Also it had one 2KB BOOT EPROM (somehow like the BIOS EPROMs in the PCs) and eight 2KB SYSTEM EPROMs (totalling 16KB) containing the Spectrum Basic. This was the very early version. Soon, the eight 2KB SYSTEM EPROMs were replaced by a single 16KB SYSTEM EPROM or even a 64KB SYSTEM EPROM containing 4 different operating systems (like Basic, OPUS, Basic w/ floppy disk etc.)

So the first most used version of CoBra would have 64KB DRAM in 4 banks of 16KB, one BOOT EPROM and one SYSTEM EPROM. The 4 banks of DRAM were named DRAM #0, DRAM #1, DRAM #2, DRAM #3. The video controller circuit was using half of DRAM #1, which contained the screen memory, in order to display the 256 x 192 pixels Spectrum image on a TV screen, in the European TV standard (625 lines interlaced, 50 frames per second).

The idea behind the design was that this computer had three different configurations:

Each of these configurations was mapping the memory in a different way. For instance, the EPROM memory (BOOT and SYSTEM) was only accessible in the startup configuration and the four different DRAM banks were mapped at different addresses in different configurations.

The original hardware manual also made available a modification in the schematics where banks DRAM #0, DRAM #2 and DRAM #3 (using 16Kx1 chips) could be replaced with a single bank of 64Kx1 chips, therefore adding 16KB RAM up to a total of 80KB RAM available for use. This was called "the 80K RAM modification". This changed the memory mapping in the three configurations, therefore the program in the BOOT EPROM needed to be changed and also the CP/M operating system needed some adjustments, but was performing better since CP/M now had about 58KB user memory available.

Now, fast forward a few years, and CoBra was taken on a parallel black market (after the "official" production stopped), where students in campuses were traficking printed circuit boards and components and building it in private as a hobby.

This is when various other improvements and modifications were "invented" by those who were assembling mainboards on their own and at the same time studying the schematics and operation of CoBra.

For instance, a modification was made where, after the 80K RAM modification, the computer was able to enlarge the standard 256 x 192 pixel screen area to a 320 x 192 pixel area usable in CP/M in text mode, allowing 80 characters (of 4x8 pixels each) per line on screen. This was done by using part of the border area left and right of the standard Spectrum screen.

All in all, CoBra was a very fertile ground for all sorts of wild experiments one could think of.