The KC 85 were models of microcomputers built in East Germany, first in 1984 by VEB Robotron and later by VEB Mikroelektronik "Wilhelm Pieck" Mühlhausen. Due to huge demand by industrial, educational as well as military institutions, KC 85 systems were virtually unavailable for sale to private customers.
Technical information
They were based on the U880CPU, with clock speeds of 1.75 and 2 MHz. There were two main lines in the KC 85 series, the KC 85/2 to /4 and the KC 85/1 by Robotron, which was a different system. In 1989, VEB Mikroelektronik Mühlhausen came up with the KC compact, but due to the GDR collapse very few units were actually produced and sold and—being a CPC clone—it was a KC in name only; thus it is usually not counted among the KC family. Unlike the Pravetz series 8personal computers, manufactured in Bulgaria, which were equipped with dedicated displays, floppy discs and good quality keyboards, the entire series used a TV set as display and a standard tape recorder as data storage. The KC 85/1 used an integrated calculator-style keyboard with small "keys" of hard plastics, while KC 85/2-4 used a separate keyboard driven by a remote control IC. The KC 85/2 was the first computer made in Mühlhausen and had only font ROMs for capital letters, and no BASIC in ROM. Later, the KC 85/3 was introduced and this one had a BASIC interpreter in ROM, freeing the user from having to load the BASIC interpreter from a cassette every time. Both systems typically had 16 KB of RAM, but could be expanded with add-on modules. The KC 85/4 had 64 KB of RAM and better graphics capabilities. All KC-series computers from Mühlhausen were capable of displaying graphics at a resolution of 320×256 pixels. But the color possibilities were limited and background color. This limitation was brought down to 1×8 on the KC 85/4, which also featured a video RAMaddressing mode and a special 4-color mode which could color every pixel independently. The colors were not paletted in any KC before the KC compact. There was no "text mode", everything had to be painted; this combined with the video RAM layout described above and ROM code made the KC 85/2-3 rather slow at printing and scrolling. There were no blitters, and the video subsystem was developed in-house. Sound and tape output was implemented by CTC channels driving flipflops. Memory bank-switching was common since the total address space was only 64 KB. When running Mühlhausen's BASIC, the video RAM was banked in only during video operations, thus the maximum BASIC free RAM was about 47 KB instead of 32 KB. The module extension system also used bank-switching and made it theoretically possible to extend to megabytes of RAM, however neither BASIC nor most of the applications were prepared to use this as free space. The KC 87 was a better KC 85/1 with BASIC also in ROM. There was a color option, but no real graphics apart from ROM pseudographic characters. The wiring diagrams are freely available and there were also a lot of different schemes and hardware parts. Various magazines published programs and hardware diagrams and also instructions on how to build them.
Programming languages
The KC 85 could be programmed in assembly language and BASIC, but it was possible to use various modules or load software from tape, thus allowing programming in Forth and Pascal. The operating system was CAOS. It was a simple monitor where one could run different "system services" like LOAD, JUMP, MODIFY or BASIC. New commands could be added to the menu by magic numbers anywhere in the memory space. In the last years of the GDR, a floppy attachment was produced. It featured a 4 MHz CPU and a 5¼" Floppy drive. These were able to run CP/M, which was called MicroDOS.. There was also a disk extension mode for CAOS.
Hobby projects
There were a lot of different projects for the KC 85:
