The first commercial hard drive was put on the market by IBM in 1956.  Made up of 50 24" metal discs, it held a whopping five megabytes.  By 1973, capacity was up to 30 MB with the revolutionary "Winchester" 3340.  However, it was still a large metal disc.

     At the same time, IBM was developing cheaper magnetic media in the form of the "floppy" drive. A sort of coated plastic, the cheaper, removable ( the "Winchester" was sealed ) medium was, well, floppy. The discs also didn't weigh several pounds or hold several MB. As they decreased in size from 8" to 5.25", they somehow got the name "diskettes".

      Of course, modern hard drive platters are much smaller than either the 70's monstrosities or the "diskettes" of the day. Sometimes they're "disks" (short for diskette) sometimes they're "discs" (short for discus). I'm on the "disc" side of the argument, myself. Modern hard drives use sealed discs with heads that float on a cushion of air, just like the IBM "Winchester." They're obviously not descended from diskettes.

By the way, there's no argument over CD's;  "Compact Disc" is a registered trademark.
This is supposedly one of those things where "disc" is the British spelling and "disk" is the American spelling. Most computer things come out of the US these days, so we get used to seeing "program" and "dialog" in computer contexts. Philips, inventors of the CD, are a Dutch company, so they used the British spelling, and as they got to copyright the technology everyone has to follow them for Compact Disc.

But this is not a normal British/American difference. The only other comparable pair is mollusc/mollusk. I only know two other words ending in -sc, and they're pretty obscure: subfusc and fisc. I'm not sure whether they're written subfusk and fisk in American.

The odd thing is, -sk is the natural English ending: mask, task, flask, desk, risk, tusk, musk, tusk. The C/K sound is almost always written K after another consonant: park, lurk, talk, folk, ink, bank...

The older form of the word in English would be disk rather than disc: but what it actually becomes in Old English is dish, and in Middle English it's desk and dais.

The Greek diskos meant a small round thing for throwing, a discus or quoit. It was borrowed into Latin as discus, but later came to mean a small round table. This is how it comes to be borrowed into Old English as dish, then into Middle English as desk (via the Italian form) and dais (via the French form). The dais was originally the table itself, then later the platform it stood on.

So it's the "British" spelling disc that's slightly odd - we wouldn't expect it to line up with Latinate technical terms like mollusc, subfusc, fisc; why isn't it an ordinary K word like risk, desk?

The difference between a disk and a disc is pretty simple, actually. A disk refers to a magnetic storage device that is not circular, so we have a floppy disk and a hard disk (Yeah, it's just the casing that isn't circular, I know, I know). Conversely, a circular storage device is a disc. So a record is also a disc, and we have compact discs and digital versatile discs. This is also why you listen to disc jockeys and not disk jockeys.

The fourth edition of the American Heritage Dictionary of the English Language (available via agrees.

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