Didaktik Gama was the first clone of the ZX Spectrum with one speciality: 80 KB RAM divided into two switched 32 KB memory banks and 16 KB of slower RAM containing graphical data for video output, while the size of ROM was 16 KB. This computer had become an unreachable dream for many children and adults in former socialist Czechoslovakia as the computer was considerably expensive and seldom available to buy. It is said there were waiting lists several years long. The design of the computer was very simple – just a grey or black box the size of A5 with flat plastic keyboard and connectors mounted on the rear side. All games developed for the ZX Spectrum 48K were generally compatible with this computer. There is no need to say that it established massive and flourishing black market with these games country-wide as they were officially unavailable behind the "iron curtain". An audio cassette was used as the data store and a TV served as the monitor.
Didaktik Gama was produced in three variants: the first, Gama '87, fixed some bugs in the original ZX Spectrum ROM, thus breaking compatibility in some percentage of applications (read: games), and introduced its own bugs effectively inhibiting the use of the second 32 KB memory bank from BASIC. Gama '88 fixed the original ZX Spectrum bugs in a more compatible way and fixed the memory switching bug. The last and the best model was Gama '89 which fixed some more bugs. Production of Didaktik Gama computers ceased in 1992.
Source: Wikipedia, "Didaktik", available under the CC-BY-SA License.