https://olimex.wordpress.com/2015/01/12/retro-computer-puldin-the-only-bulgarian-8-bit-computer-developed-from-scratch/
http://atodorov.org/blog/2016/07/12/testing-the-8-bit-computer-puldin/
One of the main objectives of Puldin was full compatibility with IBM-PC. At the time IBM had been releasing extensive documentation about how their software and hardware works which has been used by Puldin's creators as their software specs. Despite IBM-PC using faster CPU the Puldin 601 had a comparable performance due to aggressive software and compiler optimizations.
The guy who wrote the Assembler BIOS and Basic ROM for Puldin – Todor Todorov became more famous with his virus works instead of what he did for Puldin
[...] in 1991, an international epidemic was diagnosed. One-hundred sixty documented Bulgarian viruses existed in the wild, and an estimated 10 percent of all infections in the United States came from Bulgaria, most commonly from the Dark Avenger.