Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-06-05
2004-04-27
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S077030, C360S075000, C360S060000, C360S053000
Reexamination Certificate
active
06728050
ABSTRACT:
FIELD OF THE INVENTION
This application relates generally to the field of information storage and more particularly to a method and apparatus for verifying that data written on a storage disc can be reliably recovered during subsequent read operations.
BRACKGROUND OF THE INVENTION
The need for larger capacity data storage devices has become critical with the staggering pace of advances in computer technology. The most common data storage device used within computers today is the disc drive. The amount of data that can be stored on a disc drive has increased dramatically in recent years. Coupled with the need for larger storage capacity is a desire to increase the information throughput of the drive (i.e., increase the rate at which information is stored to and retrieved from the disc drive).
Most disc drives are composed of one or more magnetic media discs attached to a spindle. A spindle motor rotates the spindle and discs at a constant high speed. An actuator assembly adjacent to the disc(s) has actuator arms extending over the discs, each with one or more flexures extending from each actuator arm. A read/write head is mounted at the distal end of each of the flexures. The read/write head includes an air bearing slider enabling the head to “fly” in close proximity above the corresponding surface of the associated disc. The distance between the read/write head and the surface of the associated disc during disc drive operation is called the “fly height.” Information is stored on and retrieved from a disc via the read/write head.
Information is stored on the disc surface as a bit. A bit is represented by a “1” or “0,” which corresponds to a change or lack of change, respectively, in the orientation of adjacent magnetic domains on the disc surface. A domain's magnetic orientation is changed using the disc drive's write element. A write element is essentially an inductive coil. A magnetic field is generated around the write element by passing a current through the coil. The magnetic flux of the generated field, if strong enough, orients the magnetization direction of a magnetic domain located on the disc surface. The direction of the current in the write element dictates the direction of the magnetic flux of the generated field, and subsequently, the orientation direction of the magnetic domain.
As mentioned above, the strength of the magnetic field present at the disc surface must be strong enough to orient the magnetic domain. The strength of the magnetic field relative to the disc surface decreases as fly height increases. The magnetic field relative to the disc surface may not be strong enough to change the magnetic domain's orientation if the fly height becomes too great. One solution is to increase the strength of the magnetic field. The strength of the magnetic field, however, must be limited to prevent changing the orientation of adjacent domains located on the disc surface. The fly height of the read/write head, therefore, is critical to insure that the generated magnetic field is sufficient to change the orientation of the desired magnetic domain without changing the orientation of adjacent magnetic domains.
Information is retrieved from the disc surface using the read element. The read element senses orientation changes of the magnetic domains on the disc surface. The changes in the magnetic domain orientations create an electrical signal in the read element. The read element must be very sensitive to detect the orientation changes of the small magnetic domains. The disc drive's preamplifier is used to amplify the resulting signal before the signal is sent to the disc drive controller. Again, the fly height of the read/write head is critical to insure that the read element is close enough to the disc surface to detect the orientation changes in the magnetic domains such that an electrical signal is produced within the read element.
Each disc is radially divided into a finite number of concentric tracks to facilitate organization of the stored bits. Each track is a certain width and is separated from the adjacent tracks by a “blank space.” This blank space prevents information stored in one track from overlapping the information stored in an adjacent track. The number of tracks located on each disc surface is known as the “track density.” Each track is linearly subdivided into sections, called segments. Bits are written to and read from these segments by the read/write head. The linear density of bits stored within each segment is called the “bit density.”
The product of track density and bit density is known as “areal density.” The recent trend being followed by disc drive manufacturers is to increase the recording media's areal density so that the amount of data stored can be increased without increasing the physical size or the number of discs used in a drive. For example, the areal density of early disc drives was less than 1 gigabits per square inch (Gbits/sq. inch), whereas today, disc drives with areal densities greater than 40 Gbits/sq. inch are being tested. Manufacturers increase areal density by increasing both track density and bit density. Track density is increased by narrowing the track width and/or narrowing the width of the blank spaces between tracks. Bit density is usually increased by increasing the recording speed in order to record higher frequency bits. A higher frequency bit is smaller, and therefore, takes up less space on the disc surface.
An increase in areal density has a direct effect on the fly height of the read/write head. The write element must fly closer to the disc surface when writing information at higher areal density because the “blank space” and track width become smaller. A decrease in fly height is necessary to insure that the magnetic field present at the disc surface is strong enough to change the desired domain's orientation without overwriting information stored in an adjacent track. Likewise, the read element must fly closer to the disc surface when retrieving information from a disc with higher areal density because the smaller bits generate a smaller magnitude signal within the read element. The fly height, in summary, must become smaller in order for the read and write operations to be completed effectively as areal density increases.
The fly height in current disc drives has decreased to less than 1 microinch (&mgr;-in). A small contaminate particle, vibration, external shock, or a disc surface defect, among others, can affect disc drive performance at such low flying heights. For example, a dust particle that hits the read/write head can cause the read/write head to “bounce” away from the surface of the disc. If this bounce occurs while information is being written to the disc, the magnetic field generated by the write element may not be strong enough, relative to the disc surface, to change the desired domain's orientation and accurately record the information on the disc. This problem is known in the art as a “skip write” or “skip write error.”
Most disc drives are manufactured in a clean room environment in order to prevent the presence of contaminate particles in an assembled disc drive. Most clean rooms are Class
100
clean rooms. Class
100
means that 100 contaminate particles per-liter-of-air are present in the room. Class
100
clean rooms were adequate for older disc drives with higher fly heights, but current disc drives require Class
10
clean rooms. Class
10
means that only 10 contaminate particles per-liter-of-air are present in the room. The amount of filtering needed to reach and maintain Class
10
status dramatically increases the cost of the disc drive manufacturing process.
Disc drive manufacturers place filters within the disc drive to trap the contaminate particles introduced during the manufacturing process. The filters also trap contaminate particles emitted from the drive's components during normal operation. The filters require between 100 and 200 hours of normal drive operation to effectively capture the contaminate particles. A brand new drive, ho
Faber Alan T.
Merchant & Gould P.C.
LandOfFree
Capacitance skip write detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Capacitance skip write detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Capacitance skip write detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3275866