Re: Disk transfers help please

["josephoswaldgg@hotmail.com" <josephoswald@gmail.com>]

Ed Eastman wrote:
> glen wrote:
> > Traditionally, at least for IBM style drives, the index hole is only
> > during formatting.
>
> Gen:
> I think you are mistaken.  The index hole is used by the PC drive
> mechanism itself.  If the mechanism does not see a pulse every so often
> then it shuts down the drive motor.

According to the data sheets for floppy disk controller circuits (such
as the Intel 82078 or 8272A), various functions on the chip make use of
the index pulse as a time out which causes them to raise an error flag.
For instance, if it is in read mode and sees two index pulses without a
correct sector header having occured, it reports an error, and
terminates reading. The "Read Track" command and "Format Track"
commands wait for an index pulse to commence.

Whether this error causes the motor to power down is probably OS or
BIOS dependent.