Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
1998-11-13
2002-02-26
Neal, Regina Y. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S046000
Reexamination Certificate
active
06351340
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to a method of and an apparatus for erasing a magnetic disk. More particularly, the present invention relates to a method of and a device for erasing a recording track formed on the magnetic disk.
BACKGROUND OF THE INVENTION
Signals representing data are generally recorded on magnetic recording media such as magnetic disks, magnetic tapes, or the like by residual magnetism. The data on disks is written by a read/write head located in a disk drive that writes the data in concentric circles on the disk called tracks. Disk drives with removable media preferably have the capability to read and write disks from earlier generation drives (i.e., older disks). These older disks typically have a lower capacity, and therefore have wider data tracks than the newer disks. For example, a 1.44 megabyte 3.5″ floppy disk drive preferably has the capability to read and write older 750 kilobyte disks, which have substantially wider data tracks. In the older disk drives, wider read/write heads are used to read and write data to the tracks. As technology has improved and the density of data on disks has increased, read/write heads have become narrower. To be able to produce newer generation disk drives economically, the same read/write head is used to read and write both current (narrow track) and older generation (wide track) disks. Because the head's recording width matches the narrower track width of newer drives, special techniques must be used to correctly write a track on the wider tracks found in older generation disks.
FIG. 1
is a top view diagram of a wider track (from an older generation disk) that has been overwritten with a narrow head (in a later generation disk drive having a narrow head). Old data
110
along the edges of the track
101
remain after the new data
105
has been written. The narrow head writes new data on a track width WN. The wider head reads and writes data on a track width WW. The old data remaining after the narrow head writes on a track has a width of WO1 and WO2, where WW=WN+WO1+WO2. Typically, WO1 is substantially equal to WO2. The old data
110
will likely interfere with the desired signal (which comprises only the new data
105
and not the old data
110
) if the disk is read in an older drive that is equipped with a wider read/write head. When the track
101
written by a narrow head is read back by a wide head (e.g., in an older drive), both the old data
110
remaining along the track edges and the new data
105
are read back.
One method of overcoming this problem is to utilize a second erase head in the newer drive. This head is not designed to record data, but instead is designed to simply erase the track edges of the older disk's track. In other words, the recorded signals or data can be erased by removing the residual magnetism under a magnetic field generated by an erasing head positioned closely to the magnetic recording medium. One conventional way for erasing the recorded magnetic signals is known as a DC (direct current) erase process which utilizes either an erasing head with a direct current flowing through its coil or an erasing head having a permanent magnet. Such an erasing head produces a magnetic field in a prescribed direction to magnetize the magnetic recording medium uniformly until it is magnetically saturated. The DC erasing head is however disadvantageous in that it leaves noises of high level on the magnetic recording tape when erasing the recorded signals therefrom, thus increasing the distortion rate of signal waveforms which will be recorded and reproduced.
Another method that does not use a separate erase head is to first erase the entire wide track of the older generation disk before writing the data. This technique, called “three-pass write” is performed in accordance with the top view diagrams shown in
FIGS. 2A-2C
. Here, the track
101
is first erased by doing two erase passes on the wide track with the narrower read/write head
120
. On the first pass, as shown in
FIG. 2A
, old data
110
on one track edge
125
is erased by passing a DC erase current through the read/write head
120
while the head passes along track edge. On the second pass, as shown in
FIG. 2B
, the remaining edge
130
is erased. Finally, as shown in
FIG. 2C
, the new data signal
135
is written down the center of the wider track
101
by the narrower head
120
. Thus, the new data
135
is not corrupted by the old data
110
when the track is read by a wider read/write head, for example, in an older generation disk drive.
One drawback of the above described downward compatibility techniques is that the actual signal written is narrower than what the earlier generation head writes. This causes the readback signal read by the wider head to be lower. Additionally, because DC erased media still generates some noise in a readback head, the erased track edges still contribute noise to the readback signal. The result is poor signal-to-noise ratio when an older generation drive reads a disk written by a newer generation drive.
Additionally, it has been found that the DC-magnetized edges of a wide track that has been DC erased and then written with a narrow head adversely affects the edges of the written flux changes by coupling flux to the edges of the written signal that have opposite polarity to the DC field. When read by a wide head, this coupling causes an undesirable effect known as pulse-pairing, where readback pulses of one polarity are shifted early in time, and those of the opposite polarity are shifted late. Thus, leaving DC erase fields on track edges when the track is written by a narrow head degrades both signal linearity and signal-to-noise ratio.
In both audio magnetic recording and in data recording, it is known that erasing the recording medium with a high-frequency AC (alternating current) signal instead of a DC erase field results in lower readback noise. This is because DC erased media is still strongly magnetized in one direction, and any flaws in the media's distribution of magnetic particles (caused by media defects, random magnetic particle fluctuations, particle clumping, and surface roughness) will result in an external magnetic field that is picked up by the system readback head as unwanted noise.
In a prior art AC erase technique, an erasing head having a coil is supplied with an alternating current for magnetizing the magnetic recording medium as it passes the erasing head. The magnetic recording media is magnetized until it is saturated. As the magnetic recording medium travels away from the AC erasing head, the recording medium is less subject to the alternating magnetic field produced by the AC erasing head, and hence the residual magnetism on the recording medium is progressively reduced, and any residual that remains on the disk is at a frequency above the recording bandwidth, which can be removed by appropriate low-pass filtering.
Thus, the DC magnetized media causes external fields in any anomalous regions including bit edges. By erasing with an AC signal whose frequency is substantially higher than any recorded data frequency, the media magnetization switches polarity over short readback spacings, and the perturbations mentioned above cause lower external fields. Because polarity shifts frequently with AC erase, externally generated fields are smaller. This results in lower unwanted readback noise. However, conventional AC erase systems are single pass.
Although the art of reading and writing data to disks is well developed, there remain some problems inherent in this technology, particularly the integrity of data written to and read from different generations of disks and disk drives having different size read/write heads. Therefore, a need exists for a system and method for erasing unwanted data that overcomes the drawbacks of the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a system for erasing a signal in a recording track formed on a magnetic disk comprising a magnetic head for at
Iomega Corporation
Neal Regina Y.
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