Browse Prior Art Database

Improved Gray Code Pattern on a Hard Disk

IP.com Disclosure Number: IPCOM000109811D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Kisaka, M: AUTHOR [+2]

Abstract

Disclosed is an improved pattern on a hard disk to detect the position of read/write heads. To control the position of the heads, the servo pattern is written on a disk. Since the servo pattern is written in the user data area, a shorter length of the pattern is desirable. A pattern that is shorter than the prior art pattern is described.

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Improved Gray Code Pattern on a Hard Disk

       Disclosed is an improved pattern on a hard disk to detect
the position of read/write heads.  To control the position of the
heads, the servo pattern is written on a disk.  Since the servo
pattern is written in the user data area, a shorter length of the
pattern is desirable.  A pattern that is shorter than the prior art
pattern is described.

      The proposed pattern is shown in Fig. 1.  One clock bit is
assigned to 4 Gray bits in this figure.  The number of Gray bits for
one clock bit can vary for each application.  For this pattern, 10 Lm
can be used for a 4-bit pattern.  That means 6 Lm shorter than the
prior art pattern. So disk area for user data can be longer than the
prior art.

      As a read channel for a hard disk drive picks up efficient
coding like a 2-7 or 1-7 pattern, the channel can allow longer no
signal area.  Therefore, a servo pattern that has longer zero area
can be used.

      The prior-art pattern is shown in Fig. 2.  Gray code is used to
get track ID.  Each Gray bit has one clock bit and one data bit on
a disk.  One clock has two polarity transitions.  One data bit has
two transitions if the bit is 1, and one transitions if the bit is
zero.  Clock bits are used to avoid long no-signal area that might
cause extra pulses or a DC level change.  If the minimum length of a
magnet is expressed as Lm, 4 Lm is required for 1 Gray bit.  Thus, 16
Lm is required for 4 Gray bits....