The case was almost the same of the original Spectrum, and the keyboard placement was equal to the original keyboard, except for some additional commands that did not exist in the Spectrums (for characters defined by the user - UDG), and included specific Portuguese and Spanish characters such as ç and ñ, as well as accented vowels.
There were two versions: 16 KiB and 48 KiB of RAM. Inside, the same processor: Z80A running at 3.58 MHz, a ROM chip, some RAM chips (old dynamic RAMs 4116 and 4416). Microdigital did some reverse engineering to develop a CMOS integrated circuit (IC) with similar functionality to the original Bipolar IC ULA from Sinclair/Ferranti. The modulator was tuned to VHF channel 3 and the TV system was hardware selectable to PAL-M (60 Hz) as used in Brazil, PAL-N (50 Hz) as used in Uruguay, Argentina and Paraguay and NTSC (60 Hz) as used in USA and many other countries, versatility of features the ZX Spectrum never had.
Most of the software written for the Spectrum could be run on the TK 90X, but some minor incompatibilities occurred. The cassette interface ran at similar and a faster speed than the Spectrum, user selectable. Only two peripherals were released by Microdigital — a light pen interface and a parallel printer interface.
The TK 90X was replaced by the TK 95, which had a different keyboard and case, not in the rubber format, and almost the same circuit with an improved ULA chip, providing more compatibility with the original ZX Spectrum (i.e. the game Mikie runs only on TK 95, not on TK 90X). Curiously, some games became incompatible due to this modification.
Since during that period Brazilians were prohibited of importing computers, the TK 90X was a large success and became the first affordable color computer of Brazilians. Similar status, because it was designed for Portuguese and Spanish language users, was achieved in other Latin America countries, as it was very successfully exported to Uruguay through its local distributor, Ingenieria de Sistemas, and also to Argentina, Chile and Ecuador, where it competed with the Sinclair ZX Spectrum.
Because of its affordability, many commercial software programs were locally developed for the first time for use of small businesses in Latin America to run on the TK 90X, and millions of users in the same region had their first computer experience with it.