usenet@umrisca.isc.umr.edu (usenet) (07/19/89)
For some time now, people have been debating disks, disk drives, diskette densities, etc. If you have questions about disks, please read the following. The following is a list of disk sizes and formats: 3 1/2" Disks 720K - Double Sided, 80 tracks/side, 9 sectors/track, 512 bytes/sector 1440K - Double Sided, 80 tracks/side, 18 sectors/track, 512 bytes/sector 5 1/4" Disks 320K - Double Sided, 40 tracks/side, 8 sectors/track, 512 bytes/sector 360K - Double Sided, 40 tracks/side, 9 sectors/track, 512 bytes/sector 720K - Double Sided, 80 tracks/side, 9 sectors/track, 512 bytes/sector 1200K - Double Sided, 80 tracks/side, 15 sectors/track, 512 bytes/sector Note that Double Sided means that data is written on BOTH sides of the disk. Only some of the original PC's used 160K format which wrote on only one side of the diskette. Comments about 3 1/2" Disks: A 720K disk can be read on a 1440K drive, while a 1440K disk can't be read on a 720K drive. A 1440K drive can write either 720K or 1440K, and can read either. A 720K drive can read only 720K disks, not 1440K disks. The difference is all in the higher densities involved in the 1440K drive (merely a hardware function). Comments about 5 1/4" Disks: The entire problem in this size disk is in trying to mix disks with differing number of tracks on a disk. A disk with 80 tracks means that the tracks have to be half as wide as disks with 40 tracks. This means that disks which have been formatted in a high-density drive (720K, 1200K) may have problems being read in a low-density drive (320K, 360K) since the tracks are only half as wide as those written on a low-density drive. Note that the reverse isn't true - disks formatted in a low density drives can be easily read in a high density drive (since the tracks are twice as wide as expected). Some low density drives can read disks that have been formatted to 360K format but have been created in a high-density drive. Note that this process is HIGHLY unreliable. Feel free to ask more questions, just not the same ones over again. Henry henryc@cs.umr.edu