Which computer was that? I think that 20K was an unusual amount, instead of 1K, 2K, 8K, 16K, or 32K. Perhaps it was 16K with a 4K RAM upgrade.
Everyone with a Vic 20 used to always say "I have a 5K computer"
Apple ][+ and Atari 800 and Spectrum all had 48k.
Commodore 64 had 64K but if you did all your programming in COMAL (which was such a beauuuuutiful language) then you only had 20K to work with iirc. So maybe that is what he meant.