4 ms·
> Put the flux transitions too close to each other and they'll disappear Sure, but that's below the bit pattern. For the bit stream, flux transitions can never
by a1369209993 4y ago
> Put the flux transitions too close to each other and they'll disappear
Sure, but that's below the bit pattern. For the bit stream, flux transitions can never be closer together than two consecutive one bits, which is fine and happens all the time (at least for the media GCR applies to; there are other encoding that have a minimum number of zeroes between ones in addition to a maximum).
> the differential amplifier circuit used is a feedback thing. If it doesn't get input for long enough, it will start amplifying noise in the environment
Fair point, although I'd still call that a engineering issue rather than a physics one - you can write a "weak sector" to disk, and in principle read it back, it's just that the hardware in 1541 isn't up to the task, for legitimate engineering reasons but not beacause it's physically impossible.
- ajross 4y ago> For the bit stream, flux transitions can never be closer together than two consecutive one bits, For the GCR encoding here, yes (also FM and Apple's GCR). But MFM ("double density") was contemporary, in use on the same media, based on a doubled sampling rate and a minimum of two sampling clocks between flux transitions. A bunch of logic ones there is encoded "101010101010..." (and zeros would be "0101010101...", etc...). Fancier RLL hard drive controllers woulds soon push that to a minimum of three, too. (And surely higher, but by that point the flux encoding had become a trade secret behind interfaces like SCSI or ATA, so it was never documented). "It's complicated", basically
- a1369209993 4y ago> For the GCR encoding here, yes > > (at least for the media GCR applies to; there are other encoding that have a minimum number of zeroes between ones in addition to a maximum).