KC compact: The last home computer in the GDR

In the 1980s, the GDR developed an abundance of computers and calculators. Apart from the office computers, two series of devices dominate, both of which are called KC 85, although they come from two manufacturers: the KC 85/2, 85/3 and 85/4 from Mikroelektronik Mühlhausen and the KC 85/1 and KC 87 from Robotron Dresden . Both small computer series were replaced in the late 1980s; both by instruction from above: GDR operations are state-controlled and are subject to a ministry.

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Robotron turns to the educational computer A 5105, intended for schools, network-compatible and CP / M compatible. It reached series production in 1988; at the beginning of the school year 1989/90 only 1,000 pieces were produced.

And Mühlhausen turns to the KC compact. That is not wanted. A floppy disk extension has just been released for the KC 85; a two-part device with a base, which in principle is a separate CP / M-compatible computer, and the actual floppy disk drive. For the engineers, it is not exactly a matter of the heart to have to copy a western computer instead of the previous small computer line. Because while the previous KC computers were in-house developments that have no role models, the KC compact is a genuine clone of the Amstrad CPC, which has been on the market for five years (in West Germany initially as a Schneider CPC until Amstrad set up a German branch in 1988) .

The CPC is selected as a sample because, unlike the Commodore 64 and the Atari 800, it works with the Z80 processor. The GDR has been producing the U 880 for years and in large numbers. The U 880 can be found in the vast majority of GDR computers, from simple learning computers to small computers to CP / M-compatible office computers such as the PC 1715. Expensive foreign exchange would have to be paid for western chips; and the more powerful ones are covered by the import embargo, which affects all countries in the Eastern Bloc. In addition, the CPC is not equipped with a sophisticated graphics chip for quickly moving sprites (graphic objects that lie on the background) like the C64 and is therefore less complex to imitate.

When the new computer was presented at a computer conference for the first time in a large group at the end of October 1989, a few days before the fall of the wall, the enthusiasm was restrained. Especially since the speaker from Mühlhausen does not yet have the device with him.

Some have expected a 16-bit computer. Others wonder why another 8-bit computer should be built that is not compatible with the existing ones in the same performance class. Some are proud of the previous KC 85, because it is not just a clone like most computers from the Eastern Bloc, but a GDR development. Not even in the western neighboring country, in the Federal Republic, there is a home computer from our own production.

The KC compact is not bad at all. It has connections for a cassette drive, antenna output and RGB, joystick, printer, a stereo socket and an expansion port, for which a planned floppy drive is primarily intended.

It is clocked at 4 MHz, faster than the previous KC models, and equipped with 64 KB RAM, of which 42 KB are freely available. Since the processor can only address 64 KB of memory, the 32 KB ROM must be inserted into the address space, depending on the application. The operating system including BASIC is borrowed from the CPC, if only to ensure the desired compatibility with the west computer.

The author’s KC compact. Acquired in 1990. Serial number: 001244.
(Image: heise online / René Meyer)

As a video controller, the KC compact uses the CM 607, a Bulgarian replica of the original chip 6845, which various western manufacturers produce. Instead, a collector finds an apparently imported 6845 chip in one device; It is not uncommon in the GDR that, depending on availability, chips imported from the West, replicas from Eastern Europe or clones from GDR production are used, even within a model series. Like the CPC, the KC compact is not a graphics miracle like the C64, but supports a resolution of up to 640 x 200 points. This allows 80 characters per line and thus comfortable text processing.

The sound is a significant improvement. Previous computers in the GDR produced simple melodies with a beeper. For the first time, the KC compact uses a sound chip, a three-voice AY-3-8910 from General Instrument, which works among other things in the CPC. In future, it will be reproduced in the GDR under the designation U 8912.

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