Back in the "good old days" when I first got paid to play with other people's computers, every computer room had really expensive aircon, halon dumps in case of fire and a poster on the wall showing a much enlarged disc platter and head, with various bits of airborne detritus (hair, smoke particle, dust particle) to the same scale. The idea was to illustrate that they are all bigger than the gap between the platter and the head, and will all destroy the disc if they get into that gap.
Don't forget, this was when we still used removable discs that had to be stored in airtight cases - Winchester technology was still being developed.
Anyhow, I'd love to get my hands on a copy of that diagram. I've googled around, but I haven't (yet) found it on the web. I'm sure it's out there somewhere...
Can anybody point me in the right direction, please ?
Hope this helps,