Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data verification
Reexamination Certificate
2001-06-26
2004-09-28
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data verification
C360S077080, C360S048000, C360S031000, C360S051000, C324S210000, C324S212000
Reexamination Certificate
active
06798594
ABSTRACT:
FIELD OF THE INVENTION
This application relates generally to characterizing the positioning of recording heads over tracks divided into physical sectors in a disc drive, and more particularly to a position sensing system utilizing small servo sectors and side-by-side read/write (R/W) recording heads designed to, while minimally affecting performance, predict write error occurrences by sampling and analyzing recording head position data acquired from the small servo sector and side-by-side R/W recording head configuration.
BACKGROUND OF THE INVENTION
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium called a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Each surface of a disc is divided into several thousand tracks that are tightly packed concentric circles similar in layout to the annual growth rings of a tree. The tracks are typically numbered starting from zero at the track located outermost the disc and increasing for tracks located closer to the center of the disc. Each track is further broken down into data sectors and servo bursts. A data sector is normally the smallest individually addressable unit of surface area in which to store information on a disc in a disc drive and typically holds 512 bytes of information plus a few additional bytes for internal drive control and error detection and correction functions. This organization of data allows for easy access to any part of the disc surface.
A servo burst, also known as a servo sector, is a particular magnetic signature on a track that facilitates positioning of read/write (R/W) transducers or heads accurately over the tracks. Servo sectors cross track boundaries, and can be envisioned essentially as radial spokes of a wheel. The conventional format of a servo sector is as follows. The first element of a servo sector is the variable frequency oscillator (VFO) field. This is also often referred to as an AGC field. Typically, the VFO field accounts for one half the size, or length, of a servo sector. The purpose of the VFO field is to generate an on-the-fly frequency by which subsequent servo sector data can be read. Following the VFO field is typically a servo address mark (SAM), This is also often referred to as a servo timing mark, and is typically approximately 10 bits of data. The purpose of the SAM is to indicate the starting point of the servo sector data. Following the SAM is the servo sector data. This data contains track address information, describing which track the head is on. Finally, after the servo sector data is the PES (position error signal). This is also oftentimes referred to as the vernier position signal. The purpose of the PES is to provide a means for the control system to determine the center of the track for proper head positioning.
Generally, each of the multiple discs in a disc drive has associated with it two heads (one adjacent the top surface of the disc, and another adjacent the bottom) for reading and writing data to a sector. A typical disc drive has two or three discs. This usually means there are four or six heads in a disc drive carried by a set of actuator arms. Data is accessed by moving the heads from the inner to outer part of the disc (and vice-versa) driven by an actuator assembly. The heads that access sectors on discs are locked together on the actuator assembly. For this reason, all the heads move in and out together and are always physically located at the same track number (e.g., it is impossible to have one head at track
0
and another at track
500
). Because all the heads move together, each of the tracks on all discs is known as a cylinder for reasons that these tracks form a cylinder since they are equal-sized circles stacked one on top of the other in space. So, for example, if a disc drive has four discs, it would normally have eight heads, and a cylinder number
680
would be made up of a set of eight tracks, one per disc surface, at track number
680
. Thus, for most purposes, there is not much difference between tracks and cylinders since a cylinder is basically a set of all tracks whereat all the heads are currently located.
One of the heads must first be positioned over the correct location of a sector on the disc in order to access (i.e., read from or write to) the sector. This requires the heads to move to the correct track and then wait for the correct sector to pass under the appropriate head. Moving the heads to the correct track is referred to as a seek. Once a seek has finished and while the disc rotates to a correct sector, the servo mechanism continuously interprets servo sector information from the track to ensure the head remains positioned correctly. Essentially, servo sectors, also known as servo bursts, aid in steering the head over the track.
FIG. 3
is a schematic representation of a conventional servo sector
200
recorded on a disc in a sectored servo control system scheme. Five typical concentric tracks
202
,
204
,
206
,
208
, and
210
are pictured sequentially in the vertical direction. The horizontal lines in
FIG. 3
indicate the track boundaries. The servo sector format is interpreted from left to right partitioned bit-wise. The first field is simply a 2 bit gap
212
. The gap is used to indicate separation of the servo sector from the previous data sector. The second field is the variable frequency oscillator (VFO) field
214
. The VFO field
214
is typically equal to half the length of the entire servo sector
200
. The purpose of the VFO field
214
is to generate a frequency for the data sampling rate to lock onto in order to precisely time the reading of subsequent servo sector information bits. Following the VFO field
214
is a servo timing mark, or servo address mark (SAM)
216
. The SAM
216
is typically 10 bits in length and indicates the start of subsequent servo sector information bits. Following the SAM
216
, there are several bits of information indicating the track
152
address according current precise location on the disc
108
. In the illustrated format, there are 18 bits of track address information
218
. Following the track address information
218
, there are 12 bits of vernier position error signal normal (PES_N)
220
, followed by 12 bits of vernier position error signal quadrature (PES_Q)
222
. The PES signals
220
,
222
, are used to steer the recording head affixed to the actuator assembly over the center of the track, e.g. track
204
. Finally, there are 2 additional bits of gap
224
.
Recording transducers or heads consist of two elements: a read element, or reader, and a write element, or writer. Conventionally, the reader and writer element are positioned sequentially in a recording head. This is also referred to as a piggyback configuration.
FIG. 5
is a schematic bottom view of a convention piggyback recording head
300
and a corresponding track
204
on a disc. The reader and writer of the recording head
300
are oriented such that they fly over the same track. The reader and writer each has a corresponding read gap
304
and write gap
302
. Due to the piggyback configuration, a distance
306
, typically 5 &mgr;m, separates these gaps. Also pictured is a track
204
with data sectors
226
surrounding a servo sector
200
. During operation, the disc rotates such that the track
204
passes under the piggy-back recording head
300
from right to left in the direction indicated by the arrow
308
. A piggy-back recording head
300
can only read or write at any given time, and since a piggy-back recording head
300
must first read a servo sector
200
before it may write the subsequent data sector
226
, a gap
306
equal to the distance between the read gap
304
and write gap
302
also exists on the disc media as shown.
Thus, as the disc passes under the head, the reader reads servo information until a data sector is to be read or written. When a data sector is to be written, the disc rotates until
Berger Derek J.
Hudspeth David
Lucente David K.
Rodriguez Glenda P.
Seagate Technology LLC
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