DOS feature on formatting disk

for media portability the track 0 was the directory on some IBM formats, and probably the dos program is trying to bridge the problem by forcing the whole track to have readable sectors on it, so some other non dos programs won't blow. I had experience doing a 8" driver at one time and was surprised to find that the standard format for ibm was to have at least the first sector present, but the rest could be "deleted" sectors, the lot of which could be replaced with other data sectors, and a string of deleted ones again to add data. Also track 0 frequently tells software that the format is for the entire disk, and may have been assumed to be in a standard density, with tracks 1 thru n in a different density, determined from track 0. I think on 5 1/4" diskette formats IBM did look at a byte in the first sector to tell 320 vs 360 or 160 vs. 180 k format. Later bios' assumed a 360k format if the byte was not FF or FE, IIRC. Some non dos os's were smart when designing their disk formats to be used inthe IBM pc and kept the media byte, and some, (like Pick for the PC) were dumb and had diskettes which looked totally unformatted to the bios and to DOS when set up for their use. Jim "Dwight K. Elvey" wrote: