meulenbr@cstw68.prl.philips.nl (Frans Meulenbroeks) (06/28/90)
Hi! I have a hard disk (Micropolis 1355) which has a jumper to let the drive operate in either hard or soft sectored mode. My controller (Adaptec 4550A) also supports both hard and soft sectored drives. Can anyone tell me the difference between hard and soft sectoring, with respect to hard disks (I know the story about index holes), and can someone advise me what the best choice is. Thanks! Frans Meulenbroeks (meulenbr@cst.philips.nl) Centre for Software Technology ( or try: ...!mcsun!phigate!prle!cst!meulenbr)
guest@masscomp.ccur.com (Mr Guest) (06/28/90)
Hard sectored disks derive their sector pulses by dividing the internal servo clock by the number of servo clocks per sector. Index is usually derived by having a certain pattern recorded in the servo clock data recorded on the servo track. Decoding this pattern will provide an Index pulse, and everytime the counter reaches the sector size count a sector pulse will occur. Index will reset the sector pulse counter so the first sector is always full size and the last sector is usually shorter than full size. The Sector and Index pulses are based on the servo clock with little or no control from the controller. Soft sector drives rely upon a DC-erased segment of the data on each track to encode the beginning of a sector. Data is recorded in MFM ( Modified Frequency Modulation ) so even if you wrote 512 bytes of zeros, the actual data on the disk would still have many flux reversals, and would not be mistaken as an Address Mark (the DC-erased segment of data). The Sector and Index Pulses are still based on the servo clock, but now the Index is encoded and decoded by the drive, the sector is encoded by the fact that an Address Mark was written under command of the controller, the sector is decoded by the drive detecting an Address Mark, and not derived by dividing servo clocks. IMHO hard sector drives are more reliable. The Address Mark detection sometimes causes internal controller problems especially if there is a media defect in the Address Mark field. Sheldon Kolansky