Historically, that would be anything on a FAT drive: DOS, OS/2. I'm sure that back in '95, '96, some may have included Win95 in the list as well, being a bit scared of the new extentions to the FAT filesystem therein. (I'm just waiting for my last OS/2 machine to die on me ... going on 7 years old :-})

Today, with DOS a mere memory that is fading, at least for most people, and OS/2 being officially withdrawn from the marketplace (for the fourth or fifth time, I think, if one were to believe the tech-news), or even the very small numbers of OS/2 users that still use FAT (HPFS being far, far superior in every way), I'm not sure what reason is left for short names.

That said, I still see value in differentiating our 'bare' words: often we use UPPERCASE for constants (or constant subs) and perlish APIs (e.g., DESTROY, BEGIN, END), or lowercase for scope-limited variables. CamelCase for packages, and under_scores for functions works for me.