Browse Prior Art Database

Sector-to-Sector Motor Speed Protector

IP.com Disclosure Number: IPCOM000123338D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 82K

Publishing Venue

IBM

Related People

Cadloni, GL: AUTHOR [+3]

Abstract

A method to reduce the number of format overhead bytes on a hard disk drive (HDD) is disclosed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Sector-to-Sector Motor Speed Protector

   A method to reduce the number of format overhead bytes on
a hard disk drive (HDD) is disclosed.

   Present art in the field of HDD track format has the
format designed to allow a write or read of a data sector, a
predetermined length from a servo timing mark, while the motor speed
is within a predetermined threshold tolerance.  The predetermined
length from a servo timing mark usually has to include the "normal
distance between servo marks plus an additional distance due to
missing servo marks.
                Sector 1        Sector 2     Sector 3
                  |               |             |
  Servo Mark      |-100usec nom.--|-100usec nom-|-100usec nom----
  Speed error    -.1%            -.1%          -.09%
                               10usec|-|
                                     ______
  Write Gate     ___________________|      |__________________

   Figure 1

   Figure 1 shows an example where a write is occurring
just after servo sector 2.  The counter that determines when the
write should start is reset every time a sync mark is found.  In this
example the write gate is referenced to sector 2.  Since the counter
runs off an oscillator based clock and the servo marks written on the
surface of the disk are subject to motor speed tolerance, the exact
place on the disk where the write gate will occur varies
proportionally with amount the motor speed is off from its nominal
speed value.  In this example the write gate will be (10usec*.1%)
10ns off due to the motor speed error.  This amount of variation is
not a problem to accommodate in the format.  However, to improve the
robustness of the servo system a finite number of servo marks can be
missing (this is due to disk defects and noise hits).  Figure 2 shows
the effect of a missing servo mark.
                 Sector 1        Missing 2     Sector 3
                   |               X             |
  Servo Mark       |---100usec-----X----100usec--|---100usec--
  Speed Measure  -.1%             ??           -.09%
                   |----110usec------|
                                     ______
  Write Gate     ___________________|      |__________________

   Figure 2

   Figure 2 shows an example where a write is occurring
just after servo sector 2.  The counter that determines when the
write gate should start cannot be reset at servo mark 2 because it is
missing.  The counter is stil...