The first MS DOS version of Tetris was implemented a few days after Alexey put together his first prototype of the game for the Electronica 60. All three of us - Dmitry, Alexey, and I - were fans of Pascal and structured programming despite then-recently-published text "Real Programmers Don't Use Pascal". We used various flavors of Pascal to implement our game ideas. Under MS DOS the development system of choice was Borland's Turbo Pascal. I started learning programming with v1.0. In fact, I still enjoy programming in the descendant of Turbo Pascal - Borland Delphi. The last version of Tetris, we worked on together, was compiled with Turbo Pascal 4. That last version of the game had number 3.12. Although 3.12 is pretty much an arbitrary number as we did not have a strict versioning policy. By the way, this version has an Easter Egg. Although not a sophisticated one. I wonder if anyone can discover it.
The MS DOS version is quite different from the Electronica 60 draft which initially had just the glass and a score count. That version worked on a monochromatic (green/black) alphanumeric display. The tetramino squares were drawn as a pair of square brackets [ ]. Remarkably, the game was playable and addictive even in that form. This gave us a reason to hurry up with the MS DOS implementation. I believe Alexey expanded his Electronica version of the game after we ported it to the PC to match some of the features we had in our PC games. I never worked with Electronica computers myself.
We diligently implemented the MS DOS version of the game in such a way that it could run on any PC we had available. The program ran in a text mode using colored space symbols to represent squares of teraminos. The game could even automatically recognize the IBM monochrome card adjusting the way it drew (printed) on the screen. The clock-frequency race had already started with the introduction of IBM PC AT and PC clones. Many games released for the earlier PC and PC XT (4.77 MHz) models ran too fast on the newer machines. The last version of our game was one of the first to use proper timer delays. 20 years later the same program still runs without any changes, looks and feels the same (especially in the full screen DOS box).
Source: The Developer Website. --Vadim Gerasimov