dan@hpnmdla.HP.COM (Dan Pleasant) (02/01/91)
Here's a wildly arcane questions for all the Mac disk experts on the net which I'm asking for a friend who does not have net access. As the last step of disk initialization, the system makes a call to DIZero(), which writes zeros on all the sectors of a disk. How does DIZero() know how many tracks/sectors to zero out? For a floppy disk, I assume DIZero() just queries the hardware to find out what kind of foppy is in the drive. But what about removeable hard disks and other non-floppy drives? My friend, who has spent some time trying to figure this out, claims that he has seen the system zero out 1004 (hex) blocks on a large drive and 1008 (hex) on a smaller drive, which seems strange to me. Anybody know the internals of DIZero()? What in the world is it doing? Many thanks to all responders. If there is interest, I'll be happy to re-post the answer to the net. Dan Pleasant
time@tbomb.ice.com (Tim Endres) (02/02/91)
In article <450016@hpnmdla.HP.COM>, dan@hpnmdla.HP.COM (Dan Pleasant) writes: > As the last step of disk initialization, the system makes a call > to DIZero(), which writes zeros on all the sectors of a disk. > How does DIZero() know how many tracks/sectors to zero out? > For a floppy disk, I assume DIZero() just queries the hardware > to find out what kind of foppy is in the drive. But what about > removeable hard disks and other non-floppy drives? The code simply looks in the Drive Queue data structure for the drive that is being zeroed for the number of Macintosh sectors on the drive. Since DIZero() works through the drive's driver, the driver handles mapping these Macintosh sectors to the appropriate device sectors. tim. ------------------------------------------------------------- Tim Endres | time@ice.com ICE Engineering | uupsi!ice.com!time 8840 Main Street | Voice FAX Whitmore Lake MI. 48189 | (313) 449 8288 (313) 449 9208