bskendig@phoenix.Princeton.EDU (Brian Kendig) (02/01/90)
For a hard drive to be used with a Macintosh Plus, use a sector
interleave ratio of 3:1. For an SE, use a ratio of 2:1. For any
other kind of Macintosh, use a ratio of 1:1.
When in doubt, use the lower ratio (e. g. if in doubt between 2:1 or
1:1, use 2:1).
The `interleave' determines the spacing of the sectors on a hard
drive. For an interleave of 1:1, Sector 1 is right next to Sector 2.
For an interleave of 3:1, Sector 3 is the third sector from Sector 1.
The faster data can be read, the closer the sectors may be placed.
Remember that the cylinder in the drive is always spinning; by the
time a controller has finished reading and processing data from one
sector, the cylinder has spun so that the heads are now placed over
another sector farther away. The closer that sequential sequential
sectors are to each other the faster they may be gotten to, but if the
cylinder spins past a sector before the drive is ready to read it, it
must wait for the cylinder to make another full revolution before it
can reach that sector again. Thus, cylinders that are *too* close
will slow the drive down.
The optimal interleave for a drive is a function of the computer with
which it is used and, to a lesser extent, the characteristics of the
drive itself.
<< Brian >>
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