8" Floppies

Well, what I apparently missed is that the intent was to use both sides of a diskette in a single-sided drive, right? That is the only way that the direction would have been reversed. It seems to me that DEC did rotate the data in opposite directions in opposite sides on some models, didn't they? I've never tried to use a floppy on a DEC machine, so I plead ignorance. I'm not at all sure how any of this stuff would work out otherwise. Incidentally, for 8" media at least, (since there's little confusion about rotational rate and data rate) there's no reason why there has to be any difference between SD and DD media, since the flux reversal density is the same in FM as in MFM. The certification of the media for two-sided use, however, is important, since it's conceivable that one side of a SS diskette could have a contaminated emulsion, which would certainly be a defect disqualifiying it for the two-sided use. VERY old drives needed nearly 250 ns of precompensation, however, while newer ones needed between 125 and 180. I typically used a 6 MHz oscillator to time the precomp on 8" diskettes, and that worked out remarkably over a wide range of drives. Back in the '70s diskettes often were priced at nearly $10 each, and we often tried to save a buck or two by punching holes in the appropriate place in a SS diskette's jacket in order to make it work as DS. This worked better than half of the time. Punching the hole so the "other" side of a SS diskette could be used SS produced disappointing results too. Neither approach was useable for work paid for by others. I think that's because emulsions did get messed up that's not right, but there must have been some reason. Dick ----- Original Message ----- From: "Don Maslin" <donm(a)cts.com> To: <classiccmp(a)classiccmp.org> Sent: Friday, August 31, 2001 3:32 PM Subject: Re: 8" Floppies different on media. VERY 50 I've sensors.