The structure and operation of hard disk drives is generally known. Hard disk drives include, generally, a case, a hard disk having magnetically alterable properties, and a read/write mechanism including Read/Write (RW) heads operable to write data to the hard disk by locally alerting the magnetic properties of the hard disk and to read data from the hard disk by reading local magnetic properties of the hard disk. The hard disk may include multiple platters, each platter being a planar disk.
All information stored on the hard disk is recorded in tracks, which are concentric circles organized on the surface of the platters. FIG. 1 depicts a pattern of radially-spaced concentric data tracks 12 within a disk 10. Data stored on the disks may be accessed by moving RW heads radially as driven by a head actuator to the radial location of the track containing the data. To efficiently and quickly access this data, fine control of RW head positioning is required. The track-based organization of data on the hard disk(s) allows for easy access to any part of the disk, which is why hard disk drives are called “random access” storage devices.
Since each track typically holds many thousands of bytes of data, the tracks are further divided into smaller units called sectors. This reduces the amount of space wasted by small files. Each sector holds 512 bytes of user data, plus as many as a few dozen additional bytes used for internal drive control and for error detection and correction.
Typically, these tracks and sectors are created during the low level formatting of the disk. This low level formatting process creates the physical structures (tracks, sectors, control information) on the disk. Normally, this step begins with the hard disk platters containing no information. Newer disks use many complex internal structures, including zoned bit recording to put more sectors on the outer tracks than the inner ones, and embedded servo data to control the head actuator. Newer disks also transparently map out bad sectors. Due to this complexity, all modern hard disks are low-level formatted at the factory for the life of the drive.
The ability to store and access increased amounts of data depends on the ability to accurately position the RW head relative to the data tracks. Positioning of the RW head relative to the physical structures is typically based on amplitude information of two (2) or four (4) bursts within a servo pattern. This amplitude information is subject to noise, and environmental changes. A four burst amplitude servo pattern is illustrated in FIG. 2. For example, when the RW right head is located over center of the N−1 track of FIG. 2 a maximum “A” signal amplitude, minimum “B” signal amplitude, and “C” and “D” signal amplitudes that are approximately equal are sensed. The amplitude of bursts “A”, and “B”, must allow the disk controller to determine whether the head is over an even or odd track while the “C” and “D” signal amplitudes allow the controller to determine the distance how well centered the head is relative to the track. The amplitudes of signals “A”, “B”, “C”, and “D”, associated with varying track position is shown in FIG. 3A.
In FIG. 3B a servo signal is shown on an individual track. As can be seen the servo signal contains a preamble sync mark, and gray code information prior to the a four bursts, this case the amplitudes of the “A” and “B” signal bursts are approximately equal. The “C” burst is at a maximum while the “D” burst is at a minimum. Returning to FIG. 2 this would correspond to the RW head being located midway between track N and N−1 where the “A” and “B” amplitudes are approximately equal. The “C” amplitude signal is at a maximum while the “D” amplitude signal is at a minimum. The data portion of the servo signal follows the four bursts.
This four burst pattern does not allow all the disk space to be effectively used. This servo pattern requires unused media leaves less user data space on the media for storage. To realize additional storage availability, require higher data density is required which may result in a poor quality and production yield.
Further limitations and disadvantages of conventional and traditional RW head positioning processes and related functionality will become apparent to one of ordinary skill in the art through comparison with the present invention described herein.