Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-05-15
2003-02-18
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S275300, C369S044260
Reexamination Certificate
active
06522604
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to dynamic information storage and retrieval units, and more particularly to precise and efficient storage of timing and control information in the media structure of such units. The invention may be used on storage units employing rotating disks of magnetic, optical, or other media types. The inventor anticipates that the primary initial application of the present invention will be in the creation of clock information for use in writing servo tracks on magnetic media during assembly of rotating rigid disk storage units such as computer hard drives.
BACKGROUND ART
Dynamic data storage and retrieval has become of very great importance in our increasingly information based society. In both our work and enjoyment we typically use computers or computerized systems which read and write data on various storage media contained in removable or installed (“fixed”) storage units. Users of such storage systems typically want to handle a lot of data both efficiently and safely, and at low cost. Today a ubiquitous example off a storage unit generally meeting these criteria is the hard disk drive (hereinafter “hard drive”). Worldwide some 200,000 hard drives are manufactured every day.
Hard drives consist of one or more spindle mounted disks which have magnetic media on one or, more typically, both major sides. The terms “disk pack” and “disk platter” (or even simply “platters”) are widely used terms for an assembly of such disks. A motor is provided to rotate the disk assembly and arms bearing read/write heads (“R/W head”) are positioned pivotally or linearly above the media to magnetically write or read data into and from the media (an: assembly of such arms and R/W heads is commonly termed a “head stack”). To efficiently and reliably later access user data a scheme of concentric tracks and sectors within those tracks are defined during hard drive manufacturing using a process called “servo track writing.” This process places servo data in a proprietary coding in the disk media called a “servo pattern.” Data storage density in hard drives thus very much depends upon how densely such tracks and sectors can be defined and reliably used. Hard drives coming available today have track densities as high as 10,000 tracks per inch (TPI), and manufactures hope to obtain 20,000 TPI in the next 3-5 years.
Accurately manufacturing hard drives economically and in large quantity is not easy. For example, due to the limitations of mechanical tolerances inherent to manufacturing, the actual speed of rotation of disk platters is not exactly the same in every unit produced. If a hard drive is designed to optimally store n sectors of data in each track, platter revolution speeds that cause n−2 or n+3/4 sectors to be written can cause unexpected and even disastrous results (often at some later point outside of the closely controlled manufacturing environment). Such variation can be termed “sector-inconsistency error.” Of course, the hard drive can be designed with tolerances to accommodate an expected degree of sector-inconsistency error, but that seriously undercuts the goal of achieving a high data-per-track storage density.
Further, similarly due to manufacturing limitations, the disk platter rotation is never perfectly circular. If this imperfection is severe enough it can even cause the coding to be mistakenly written to a different data zone, called an “off-track error.” One solution for this is to allow the physical width of the track to be such that the possibility of off-track error becomes negligible, but this reduces the TPI and seriously undercuts the goal of achieving a high data-per-platter storage density.
To address these problems, and to a lessor extent others as well, the industry has turned to putting clock information into hard drives prior to writing the servo information.
FIG. 1
(background art) is a simplified depiction of this (as noted above, actual hard drives are typically much more complex than this, but this simplification illustrates the necessary principles of operation). Within a workpiece hard drive
1
(shown only in pertinent detail) a media disk
2
rotates on a hub
3
. A clock arm
4
bearing a clock head
5
is then introduced and a clock pattern, i.e., a clock track
6
, is written at the outer periphery of the media disk
2
. Once the clock track
6
is written, the clock head
5
is used to read it back and the regular R/W head
7
of the hard drive
1
is used in a synchronized manner to write the desired servo pattern into the media disk
2
.
A servo pattern may also be complex. It may be embedded throughout the data storage area on the media disks or placed on a single media surface dedicated to it (a servo pattern is intentionally not shown in any of the drawings herein because of the confusion which doing so might cause; also, an older wedge servo system has been used in hard drives but is now obsolete). However, it should be noted that in a hard drive only one clock track is needed.
The process of writing the clock pattern and the servo pattern is quite complex, and requires extremely precise timing, measurement, and positioning. First the clock pattern must be written. The platter of media disks is brought up to its operating speed, which commonly will be 5,400, 7,200, or even 10,000 rpm, and an initial clock pattern is written using the clock head. However, this initial pattern usually has one clock increment which is less than or greater than the others (e.g., n−1/2 or n+3/4), and in extreme cases the number of clock increments may even be less than or greater than desired (e.g., n−1 or n+2). Therefore, to create consistent clock information, the initial clock pattern is read back as a measurement of actual hard drive conditions, calculations are performed to determine what is needed to obtain a clock pattern with the desired number of consistent increments, and based upon this a final clock pattern is written.
Next, the media disks are maintained at operating speed and the clock head, which is still introduced to the hard drive, is used to read back the clock pattern while the R/W heads are used to write the servo pattern. Feedback from the clock pattern is used to write the servo pattern in a manner such that data will later be stored in a desired and consistent number of sectors. Concurrently, this feedback from the clock pattern is also used to insure that servo track writing accurately follows the rotation of the disk and that the R/W heads are adjusted to write the servo pattern in a more perfect circle. During this process feedback techniques are used to measure and position the actual R/W heads very accurately during the actual servo pattern writing. Today, laser interferometry generally is used for this but some manufacturers also employ optical encoders.
Unfortunately, there are a number of problems, compromises and lost efficiencies associated with the above-described use of a magnetic disk based clock pattern. It should be appreciated that the clock head and clock pattern are used only in hard drive assembly. Obviously, if the area used by the clock pattern, i.e., the clock track, could otherwise be used for data storage this would increase the storage capacity of the hard drive. Further, because the clock head and the associated electronics for it are expensive and cumbersome, hard drive manufacturers understandably prefer to make these part of the external manufacturing apparatus, rather than include instances of them in every hard drive being produced. But this means that the clock head must specially be introduced into the hard drive during assembly, slowing the assembly process, and perhaps more importantly putting tooling and product in harms way (those familiar with the art of magnetic recording will readily appreciate that for the clock head to write and read the media surface it must be brought very close, typically on the order of 6 micro-inches).
However, to the inventor, based upon his own years as a provider of equipment to many of the largest
Excel Precision Corporation
Intellectual Property Law Offices
Neyzari Ali
Roberts Raymond E.
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