Dynamic magnetic information storage or retrieval – General processing of a digital signal – Address coding
Reexamination Certificate
1999-06-23
2001-12-04
Hindi, Nabil (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Address coding
C360S048000, C360S077080
Reexamination Certificate
active
06327105
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic storage media and, more particularly, to apparatus and methods for low overhead, highly reliable determination of the position of such a storage system.
BACKGROUND OF THE INVENTION
Media for recording and reading information are ubiquitous in electronic equipment such as computers, digital cameras, and the like. One type of such media is a flexible data storage disk having a magnetic recording layer disposed over a non-magnetic substrate layer. Examples of these flexible disks include the type commonly referred to as a “floppy disk,” a ZIP disk (manufactured by the assignee of the present invention), and the like.
Magnetic disks typically have an “embedded servo,” wherein data regions having data and control signal regions having servo information for controlling the position of the magnetic head, are recorded alternately to constitute a recording track. During a process commonly known as “servo-writing,” servo information is embedded into the magnetic layer of the magnetic disk. The servo information typically defines substantially concentric, circular tracks. Often, servo information is embedded in a sequence of quadrature servo patterns. Each pattern typically comprises four servo pulses, or bursts, each of which is offset from the neighboring servo burst. Such an embedded servo type disk has an advantage with respect to data recording density, as compared with magnetic disk apparatus in which the track on which the data are recorded and the tracks on which the servo signals are recorded are formed separately on the magnetic disk.
In a conventional embedded servo type magnetic disk apparatus, a read/write control signal, namely the index sector pulse (ISP) signal, is produced in response to the servo information from the control signal of the track, and the read data are transferred to an external unit (e.g. a host computer) in response to the generation of the ISP signal (concerning the “data transfer” operation).
In the conventional magnetic disk apparatus employing embedded servo, one index sector pulse signal functioning as the base point for the read/write control is outputted in response to the servo information which has been read out from the servo (control signal) region of the recorded disk plane. That is to say, in response to signal edges of the servo information S
n
,S
(n+1)
and S
(n+2)
, the index sector pulse signals ISP
n
, ISP
(n+1)
, and ISP
(n+2)
are formed. In response to these ISP signals, the read/write controls for the corresponding data ID
n
, ID
(n+1)
,ID
(n+2)
are performed. In other words, a single read/write operation is carried out with respect to a single servo region. This process is described in greater detail in U.S. Pat. No. 5,313,340.
To determine head location relative to a track centerline, a head or transducer measures the signal from each burst. A position error signal (“PES”) is determined by comparing the amplitude of the signals read from neighboring bursts. The PES is proportional to the difference between the signal amplitudes of the neighboring bursts, divided by the sum of their signal amplitudes. Thus, the PES represents the offset distance between the head and track centerline as defined by the servo information embedded in the disk. The PES is then used as part of a closed loop servo system to correct the position of the head with respect to the track.
There are known methods for determining the position of a magnetic medium but these methods typically require a relatively significant amount of overhead to be reliable. That is, these methods typically require a relatively high number of bits on the medium dedicated to positional determination. Thus, there is a need in the art for a highly reliable, low overhead method for determining the position of a magnetic storage medium.
SUMMARY OF THE INVENTION
A highly reliable, low overhead method for determining a position of a magnetic storage medium that is divided into a plurality of servo sections includes defining a predetermined bit pattern that corresponds to a known position of the magnetic storage medium. A positional index bit is associated with each servo section such that a known bit of the predetermined bit pattern is associated with the known position of the magnetic storage medium. A current positional index bit is read from the magnetic storage medium and a positional bit sequence comprising the current positional index bit is formed. A shift register is used to form the positional bit sequence by storing a preexisting bit sequence, eliminating the most significant bit of the preexisting bit sequence to form a temporary bit sequence, and appending the current positional index bit to the temporary bit sequence. The positional bit sequence is compared with the predetermined bit pattern and, based on the comparison, whether the position of the magnetic medium is the known position can be determined.
To determine whether the magnetic medium is at one of several known positions, a method according to the present invention includes defining a set of predetermined bit patterns wherein each predetermined bit pattern corresponds to one of the several known positions. The positional index bits are associated with the servo regions such that a known bit of each predetermined bit pattern is associated with the corresponding position of the magnetic storage medium. The positional bit sequence is compared with each predetermined bit pattern within the set and, based on the comparison, whether the position of the magnetic medium is one of the known positions can be determined.
The length of the bit patterns, as well as the patterns themselves are defined based on an allowable number of bit errors. To determine the bit patterns, a distance between bit patterns is calculated based on the allowable number of bit errors. The distance is twice the number of allowable bit errors. The set of predetermined patterns is then determined such that every predetermined bit pattern in the set differs from every other bit pattern in the set by at least the calculated distance. A set of four, nine-bit patterns (001110101, 010110011, 101001101, 101111011) is provided for an application wherein the number of allowable bit errors is two. Note that every bit pattern in the set provided above differs from every other pattern in the set by at least four bits.
A data storage medium according to the present invention has a servo pattern comprising a plurality of servo sections. Each said servo section represents a portion of the magnetic storage medium. A single positional index bit is associated with each said servo section. The servo pattern is written onto the storage medium such that the positional index bits of adjacent servo sections form a predetermined bit pattern that is associated with a known position of the magnetic storage medium.
The data storage medium can then be used in a method as described above for determining whether the magnetic storage medium is at one of a plurality of known positions. First, a current positional index bit is read from the storage medium. A positional bit sequence comprising the current positional index bit is formed from the positional index bits of the adjacent consecutive servo sections. The positional bit sequence is compared with the predetermined bit pattern and, based on the comparison, whether the data storage medium is at a known position can be determined.
REFERENCES:
patent: 5285327 (1994-02-01), Hetzler
patent: 5311376 (1994-05-01), Joan et al.
patent: 5313340 (1994-05-01), Takayama et al.
patent: 5796543 (1998-08-01), Ton-That
patent: 5852523 (1998-12-01), Jung
Hindi Nabil
Iomega Corporation
Neal Regina Y.
Woodcock & Washburn LLP
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