"Hard disk" vs. "Hard drive" vs. "Hard disk drive"

Recently, I experienced a communication failure talking to somebody about a "hard drive" until I could actually show the person what I was talking about.

"Oh, a hard disk! I thought you were saying something else, like 'hard drive.'"
"Yes, I probably did say hard drive."

What difference is there between these two, if any?

The title of the Wikipedia article uses the less concise "Hard disk drive" which I've also used, and could be disambiugated in this question/answer as well.

Here is a Google Ngrams view of the two terms, showing that "hard disk" used to be more common but "hard drive" is increasing in popularity and the edge that "hard disk" has now is mostly attributable to the fact that it comes first in "hard disk drive."

Cross-link to related question: Etymology of the use of "Drive" to refer to a digital storage medium

Solution 1:

Hard disk refers to the data storage elements themselves.

Hard drive and hard disk drive refer to the data storage elements plus all the electronics that support, or drive, the reading and writing of data to/from storage. If, for example, the power electronics were removed, you'd still have a hard disk but not a hard drive.

The difference between hard drive and hard disk drive is that the former is more concise.

Edit (thanks to Misneac's comment!): The distinction becomes clearer when you consider the distinction between a floppy disk (something people used to carry around) and a floppy disk drive (a part of a not-so-portable computer that one would put a floppy disk into) or the short form floppy drive which apparently became more popular than floppy disk drive around 1991:

Solution 2:

I'm a computer engineer, and know intimately what these things are. I also know what my friends who aren't engineers understand.

From the engineering point of view, there is a huge difference between the disk and the drive, as WBT pointed out.

The difference is only important to the consumer for drives with removable disks (IOMega Zip, SuperFloppy, Drums, whatnot). For the consumer they often have a hard-enough time to distinguish between internal memory and the disk to get overly concerned with the drive/disk differentiation.

The term for the whole unit used to be 'hard disk drive', but over the years this has shortened to 'hard drive'. The recording 'hard disk' was used partly to distinguish from 'floppy disk', and partly because in its original 1960s incarnation it was really pretty hard: a 5mm thick disk of what amounted to solid iron oxide, usually mounted on a spindle, and very heavy.

Of course, 'hard disk' has itself mutated, normally to just 'disk' but more frequently nowadays to hand-waving 'cloud' terms: to 'flickr' or 'google docs'.

As for what is the difference between the terms, I'd say it depends on context. If you're working on computer parts, or in a relevant industrial setting, then there is a difference. In popular English, there is none, mostly because of (justifiable) ignorance.

Finally, of course, both terms are likely to disappear soon enough. Many computers now use "Solid State Drives" or SSDs, which have no 'disk' because they store data in (currently) Flash memory. Interesting note: Flash memory relies intimately on quantum theory.