> > > >> And yet another (possibly the most common one on computers) is to have a > >> small drive wheel that pulls the tape at constant speed across the > >> heads, and then have some other construction that drives the tape reels > >> depending on tape tension or length. Think vacuum columns or spring > >> loaded arms. > > > > That is closely related to the capstan and weakly-driven take up spool I > > think. > > I would disagree. There is no slipping clutch. Instead, the motors (on
True. I meant it was a system where the tape speed was determined by the capstan, and the reels are driven to keep the tape round up, not all over the machine room floor :-) > The actual tape movement as such, is all done by the small wheel next to > the head, which just runs the tape past the head. Which is essentailly the same as the capstan in an audio tape recorder, albeit the computer drive doesn't have a pinch roller > I've been wondering if there is some sensor of tape tension/pressure at > the heads, and this will allow the drive to figure out how much > faster/slower the reels must run, relative to each other, in order to > keep the tape tensioned. Then you can figure out tape speed across the > heads (if you care) by just observing flux changes. Only if there is something on the tape. These computer tape drives could surely record on a totally blank tape and get the right number of bits per inch. So the thing can't use the data rate at the head as a speed measurement. > > One of my VHS video recorders does something similar to work out how much > > recording space is > > left on the cassette. > > That can't be very precise... :-) It always underestimates the remaining tape (so that if it says there is 1 hour left, you can definitely fit a 1 hour TV programme on there). But it is suprisingly good. -tony
