I looked into this 20+ years ago and even then it was difficult to get any good data.If one would to attempt to recreate media of the time to see where the theoretical maximum is and what part of that could be actually used: WHere would find info on driving floppy drive head ?
Analog audio recording is not possible without an erase head. Both the erase head and the rec/play head are actually driven by AC, in the case of recording, AM modulated. This is how the initial magnetisation error of the ferromagnetic material is defeated, and the amount of default AC is known as the 'bias'. In order for this to work, the erase head has to produce an AC field that diminishes as the tape goes past it resulting in a demagnetized tape.How about realistic characteristics of audio head ?
Could audio head be used without separate erasing head, by erasing the track by read-write head ( with an appropriate drive )
The situation is completely different for a digital recording, where an erase head is not needed. There is some data available on how DCC (long defunct Philips digital audio tape format close to compact cassette) works, the head it uses squeezes multiple track within one standard audio track and does not use the erase head to record.
The outer tracks are used to produce an erased 'guard' track between the data tracks to prevent so called magnetic domain migration. Both disc side heads could be used at the same time but this was never intended by the standard, which started with single sided media only.Looking at the net resources for floppy head assembly, it looks like it has 6 signals and 3 heads, central one for R/W and two side magnets for erasing wider track.
Or am I missing something ?
If one would go for using central head for track erase, would that increase possible number of tracks ?
How about using both heads at the same time ?
There are a number of improvements made since the standard was created, notably increasing the density by using better mechanisms and heads, which made it possible to have two sides and cram more on a smaller diameter disc. It also solved the resonant wow and flutter problems the large diameter discs had on the outer tracks, due to the warping of the disc as the head was dragging along the surface.
The second element was a change in the modulation used, from FM to MFM, producing a doubling in recorded bit density. Strangely enough, RLL encoding that was popular on MFM hard discs, never made it to floppy. Instead, 'perpendicular' recording was used, which basically magnetizes the track perpendicular to the track, using some differential trickery using a slightly different head. This produces the jump from HD to ED.
Another thing which did not get used on floppies is zoned recording, i.e. constant linear density recording. This requires a different number of sectors on each track (or track group) and a variable recording or rotating speed. It was used on the original Mac... but not after that. On a 3.5" drive it increases the amount of data by 50%.
However, it's the floptical and similar technology that ended that because the leap of capacity was almost two orders of magnitude.
Speaking of disc recording techniques - I always wondered why MD (minidisc) never got a true computer version...