On which Soviet computer did Alexey Pajitnov first program Tetris?

Alexey Pajitnov first programmed Tetris on the Soviet Elektronika 60 computer. He was working at the Dorodnitsyn Computing Center of the Soviet Academy of Sciences, where researchers used the machine for technical experiments and small programs.

The Elektronika 60 was a Soviet computer compatible with the PDP-11. It had no graphical display, so Pajitnov represented the falling pieces with text characters such as brackets and spaces. He wrote the game in Pascal for the RT-11 operating system, adapting the idea from pentomino puzzles.

Pajitnov simplified the original concept from five-square pentominoes to four-square tetrominoes, creating the seven familiar shapes. After the primitive version became popular among colleagues, he worked with Dmitry Pavlovsky and Vadim Gerasimov to make an IBM PC version with color, scoring and sound. That later port is why the IBM PC is sometimes mistakenly named as the original platform.

The Elektronika 60 prototype was completed in the mid-1980s, before Tetris spread through Moscow and eventually reached computers and consoles worldwide.