Mac OS X is an impressive technical achievement; many experts call it the best personal-computer operating system on earth. But beware its name.

The X is meant to be a Roman numeral, pronounced “10.” Don’t say “oh ess ex.” You’ll get funny looks in public.

In any case, Mac OS X Lion is the eighth major version of Apple’s Unix-based operating system. It’s got very little in common with the original Mac operating system, the one that saw Apple through the 1980s and 1990s. Apple dumped that in 2001, when CEO Steve Jobs decided it was time for a change. Apple had just spent too many years piling new features onto a software foundation originally poured in 1984. Programmers and customers complained of the “spaghetti code” the Mac OS had become.