The first model in the series, the HC 900, originally designed as a home computer and introduced in 1984, was renamed to KC 85/2 in 1985 to de-emphasize its use as consumer good.

Later, the KC 85/3 was introduced and this one had a KC-BASIC [de] interpreter in ROM, freeing the user from having to load it from a cassette every time.

The KC 85/4 board was redesigned, but featured the same digital-to-analog video PCB as the previous generation.

This limitation was brought down to 1×8 on the KC 85/4 (the color cells on both the KC85/3 and KC85/4 were thus quite small compared to contemporary systems).

The KC85/4 also featured a special 4-color (black, white, red, cyan) mode which could color every pixel independently.

There were no blitters, sprites or hardware scrolling, not a single hardware register with which to influence the display drawing process, the sole exception being the blink attribute, whose frequency could be tuned by programming the dedicated CTC register and which required no CPU assistance.

The KC 85/4 was also the first capable of switching between 2 independent locations in video ram, allowing double buffering.

Sound and tape output was implemented by a CTC IC driving flipflops to generate square waves.

The module extension system also used bank-switching and made it theoretically possible to extend to megabytes of RAM (even more modules could be used by adding expansion devices, yielding sort of a tower), however neither BASIC nor most of the applications were prepared to use this as free space.

The keyboard of the KC 85/2-4 was based on the U807D, a clone of the Mullard SAB3021 used in TV infrared remote controls.

All the while the keyboard supply voltage was kept stable by a simple 9V zener diode, with which the controller IC was connected in parallel and if it remained within a certain window of current usage, 9V is what it would see.

There was still a slight difference in effective clock rate, the KC85/2 and KC85/3 skipped a few CPU cycles at the end of each scanline, to provide in a simple manner to the entire system the illusion of a horizontal resolution (including blanking) divisible by 8, the KC85/4 did not.

The wiring diagrams are freely available and there were also a lot of different (and often home-made) schemes and hardware parts.

The KC 85 could be programmed in assembly language and BASIC (the KC 85/2 had to load BASIC from tape), but it was possible to use various modules (sold by VEB Mikroelektronik Mühlhausen) or load software from tape, thus allowing programming in Forth and Pascal.