Re: Disk II Phase Question

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

Bryan--

The data on magnetic disks is encoded in changes in direction of the
magnetic field in the disk medium. The read/write head of the disk
drive can apply a magnetic field when writing to change the magnetic
field on the disk to record the data, and can sense the magnetic field
when reading. The field changes are converted by the disk circuitry to
provide a stream of 1 and 0 data, which are grouped by the Disk II
interface into bytes.

The reason adjacent stepper motor positions (also called half-tracks)
cannot be both used for storing data is that the disk area that the
write head affects is larger than the space between two half-tracks.

The read head will be influenced by the magnetic field on the track
below the head, as well as the field up to one half-track on either
side. There is no simple rule to determine what read data will result
from writing adjacent half-tracks.

One way to visualize the problem it is to imagine placing dots or
blank spaces in straight rows on a piece of paper with a large-tip
marker pen. The dots must be far enough apart so that they do not run
into each other, and so that the blank spaces between dots can be seen.
That limits the number of rows of dots that can fit on one piece of
paper.