Sinclair ZX81. First using its built-in BASIC. Curiosity about what made it tick, combined with a 'need for speed' got me into Z80 assembly. At one point used

Sinclair ZX81. First using its built-in BASIC. Curiosity about what made it tick, combined with a 'need for speed' got me into Z80 assembly. At one point used this puny machine to compute the digits of one of the largest Mersenne primes then-known to science (mid or late 80s). Not find that number of course, just produce a decimal representation of it. On its successor, the ZX Spectrum, I got into cracking copy protections, POKEs for infinite lives etc. MSX machines got me into hardware mods (RAM expansions, floppy drive replacements, repairs & much more). Didn't turn coding into a profession though. But the hacker mindset never went away.