Saturday, 23 November 2013

Orel BK-08

It was quite common practice to clone foreign computers in Russia in the 1980s and 1990s, as the copyright laws were quite "flexible" and the trade of computers between Soviet Union and the western Europe was a bit problematic. Most of these hobbyist computers were virtually unknown outside Soviet Union, though Finnish magazines sometimes reported rumors of professional CP/M and MS-DOS clones.

Nowadays it is known that a huge variety of 8-bit models had been in production. Most were based on the ZX Spectrum, a choice which is explained by the fact that Speccy was quite cheap to begin with and did not have a huge amount of dedicated chips. Some computers were produced by enthusiasts in electronics factories in-between the normal work, and some were built from scratch, in piecemeal fashion by hobbyists.

Enough documents, stamps and signatures to get you through Checkpoint Charlie.
It's not that hard to buy one from the eBay, although prices can be steep. The Orel BK-08 is one such Spectrum "clone" made in Russia in early nineties that has been lately available.

I bought the computer in its original packaging. For fans of "soviet chic", the graphics on the box and in the manuals are of course a treat. The documents go in quite a detail, and the package also included sheets of circuit diagrams, which however are bit too crudely printed to be really readable.

Besides the instruction manuals and technical documents, the box also had all the necessary cables and the Power Supply Unit. This makes the Orel a quite friendly entry into Russian retro-computing, as some other models can take a bit of fiddling to make them work, and documentation can be scarce. I was quite happy to have this model as there was relatively little hassle in getting it up and running. On the down side one might say the OREL is not as street-credible as some of the more adventurous DIY clones.

The main board. There are two more boards for the keyboard and power input.

Looking inside, there is a Korean Goldstar Z80 chip, and two brown ROM(?) chips that seem quite common in Russian computers. Compared to some other models I've seen the casing is quite sturdy and the circuit boards are clean and neatly ordered. The biggest question is of course, how has the Spectrum ULA, the only really Spectrum-specific chip, been implemented? (Though I have to add ULA is also a kind of customizable chip.) There seems to be no single ULA chip as such, so I have to assume the functionality has been replaced by a broader array of chips.

BK-08 and RGB

Although the package had all the cables, they are not exactly the same is in Europe. It seems to have been quite common in the Soviet Union to connect all peripherals with DIN-DIN cables. I managed to build a RGB-SCART connector to connect the RGB signal to my Sony TV, so I can say a little about my first experiences with the Orel.

From left to right: Power (24V), 7-pin RGB, 5-pin Tape out, 5-pin Tape in, 2x7-pin Joysticks.

Below is my cable connections but I cannot guarantee it works. My TV is not too picky but who's to say what might happen with some other display. Resistors may be needed to get the 12V down to the 3V for the Blanking pin at the display end. I used a series of resistors because one would get too hot too quickly in my opinion.

In any case, you should know what you are doing, and do not leave your retro-computers or power supplies connected without supervision!

Clockwise, from the top, the video output connector pins are (looking from the outside):

Edit: I realised this is misleading or even erroneous. The following is true if you look at your RGB-cable pins end, the one that you will stick into your Orel.

If you look at the computer video connector, that is a mirror image. I added a picture that should make this clearer.

12V - Scart RGB 16. I used resistors (5 x 33R) here, but my TV works without too.
BLUE - Scart RGB 7
RED - Scart RGB 15
SYNC - Scart RGB 20
GREEN - Scart RGB 11
SOUND - Scart RGB 6
GND - Scart RGB 5,9,13,17 or 18. One should be enough.

This should be clear!

Basic and Keyboard

The keyboard feels okay, perhaps a bit better than a Spectrum+. There's some trickery that allows the entry of "extended mode" keywords by pressing keys together with a CTRL key. Indeed, the extended mode does not seem to work even if it's sort of there.

The keyboard has cyrillic letters, but does not indicate the Spectrum BASIC keywords and generally does not follow the same terminology. Interestingly, the cyrillic alphabet has also been integrated to the BASIC ("BEISIK SISTEMA REV. 2.0") and the error messages have been localised. It's possible to turn on a RUS mode, which works much like the GRAPH mode. Both upper and lower case are included.

The keyboard module can be separated from the rest of the case, for no useful purpose.
The different "mode" (Graph/True/Inv.) keys have been given their own zone at the right of the keyboard. These keys are the only surface indication of the Spectrum heritage. The EDIT key is quite conveniently next to the cursor keys cluster. At the left side, there is a tilde key, which curiously brings up the VERIFY keyword in BASIC. Similarly, the tab key brings up... the keyword TAB, which is kind of funny.  Generally, all of the additional keys seem to work in a new "contextual" fashion, which may feel weird to a Spectrum user but is quite logical in the end. For example, READ, RESTORE and DATA have single-key commands at the right side of the keyboard, grouped into the zone that accommodates the rest of the cyrillic alphabet.

Some slight speed improvements might be expected because the memory is being handled a bit differently. (Something too technical for me to understand at the moment) I lazily eyed Orel BASIC loops side-to-side with a Spectrum emulator and it appears indeed a bit faster, but such a comparison is hardly conclusive. I also noticed the speed of the FLASH attribute is faster than on a normal speccy, but this is more of a timing issue than any indication of increased speed.

Edit: I made some side-to-side tests with the Orel and a 48k ZX Spectrum, both in BASIC and in machine code. The tests seem to confirm that the Orel is marginally faster, but the speed is not easily traceable to any obvious difference in memory speed or such. A task that takes about a minute can be expected to be a few seconds faster on an Orel.

Loading tapes, MZ80 and the Shadow RAM

A 5-pin DIN cable was included for both loading and saving.
Viewing the connector at the back of the computer, from left-to-right:


I succesfully loaded few pieces of software from my Mac soundcard. I tried Bruce Lee, Green Beret and Starion. The last one crashed, but it may be because of pressing the Z/Print screen key (feature of the game). Starion uses some border effects on starting the game, and predictably the timing was a bit off so it was not exactly true to Spectrum. But on the basis of these three games I'm actually surprised the Orel seems quite compatible with the Sinclair.

Maybe the least professional part of the packaging...
The OREL BK-08 has an interesting feature, a Shadow RAM, portion of memory that resides under the normal ROM. The only way to test is was to load the MZ80 monitor from the supplied tape. I made it into a .wav audio file and loaded this to the OREL using the Mac soundcard.

The MZ80 is the last chunk of code in the included tape. Use LOAD ""CODE to load it. (Press J, then "", then CTRL+J) When the loading has been finished, the program locates automatically in the Shadow RAM. Pressing the NMI key, the program residing in the Shadow RAM will be run.

I'm a bit clueless about the manual so I do not know how to display memory but I'm quite sure there is no disassembler. G seems to return to the program, but at least Bruce Lee refused to continue properly. The monitor exits cleanly to BASIC programs, though.

Here I have entered the MZ80 via the NMI button. X displays register contents.
As the RAM area (0000-3FFF I'm told) overlaps the screen memory, exit from the Shadow RAM handily retrieves the screen. (Edit: Except that memory area does not overlap with the screen memory, so something else must be going on here. Possibly the storage and restoring is done by the MZ80. Another explanation might be that as RAM starts from 16384, this is also the Shadow RAM address.) So the Shadow RAM should not overlap program code. The Shadow RAM also survives RESET, so it's possible to invoke the monitor as often you want as long as you don't pull the plug.

I don't know how simple it is to load your own code into the Shadow RAM. Maybe the MZ80 instruction manual describes how to save binary in such a way, but I don't read Russian. A proper monitor or assembler/disassembler residing in the shadow might even come useful. I guess I can at least have a look at how the tape file is formed if there are any clues.

All in all

Although my experiments are hardly definitive, I'm already somewhat impressed with the compatibility and the tiny improvements compared to the original computer. Of course, this is a much newer computer than any official Spectrum so it's not that surprising. Yet it is a bit unclear where the Orel BK-08 fits in the broader picture and history of speccy clones. It's not a DIY clone, nor does it seem to point to the Pentagon/Scorpion lineage either, as there are no 128k features or a new sound chip.

A very informative page about the technical features of the OREL BK-08

An amusing video about the OREL from Austria
(There's also a 3D-version for those who have the glasses.)


  1. Hi, I also got one and I built a SCART RGB cable but I don´t get a stable picture on my PAL TVs. I hear the sound but the picture is not syncing properly. May I ask if you also built your cable like that?:
    I simply connected R G and B, audio and ground directly to the Scart connector without any capacitors or resistors. I put the +12V from the Orel output to pin 8 of SCART to switch the TV into RGB mode and I connected SYNC from the Orel directly to Pin 16 (Blanking) of the Scart connector.
    Did you do it the same way, or did you do something differently?
    Thanks, Greetings roland. vectrexroli at gmail dot com.

  2. Hi Tero,

    We have set up a Facebook group for the OREL BK-08 (and other Soviet Spectrums):

    We would much appreciate it if you join us with your knowledge of (old) hardware :)

    Kind regards, Marc

  3. It is compatible with the Pentagon? That is, can I run the modern demos on this machine? (The new demos can run on Pentagon, but not on the original ZX Spectrum).

  4. Does anyone have the ROM files for this BK-08 mine are missing and id like to burn them.


    1. I guess you already found the very helpful facebook group mentioned in above comments?

  5. Hello, I am interested in purchasing older bk-08 or similar Russian computers here in the United States. The older the better. Might anyone have some ideas of where to get one from? I've scoured eBay and am looking for alternatives.

  6. Hello, I am interested in purchasing older bk-08 or similar Russian computers here in the United States. The older the better. Might anyone have some ideas of where to get one from? I've scoured eBay and am looking for alternatives.

    1. I can do no better than to point out the Facebook group mentioned in the above comments. There are numerous collectors and hobbyists interested in Orel and other Russian & east European computers.

  7. Hello,
    I need to connect a kempston joystick to an orel bk-08 joystick port. Is there any schem so that I can modify or make an adapter for that?