Method for transferring operational data between stations during a disk format process

Inserting operational data onto a magnetic disk allows information to be transferred from a servowriter station to a verifier station. This operational data allows disk specific operational data to follow the disk without separate means for attaching data to each disk. The servowriters, which cannot write information to disks at the data sector frequency, inserts the operational data into selected greycodes in the servo sectors. When the disks are verified, the operational data may be moved from the servo sectors to the data sector in the Z-tracks for more permanent storage.

FIELD OF THE INVENTION 
The invention relates to disk formatting using a servowriter. More 
particularly, this invention relates to methods of passing disk specific 
information from a servowriter to other downstream processes by recording 
the information on the disk during the servowrite process. 
BACKGROUND OF THE INVENTION 
A magnetic disk is commonly used in computer systems as a data storage 
medium. However, before the magnetic disk can be used by a disk drive, the 
disk must be formatted. The typical magnetic disk may be formatted to 
contain thousands of "tracks" of information, organized as concentric 
rings on the disk surface. These tracks must be precisely followed by the 
disk drive's read/write electronics during the operation of the disk to 
store information to and read information from the disk's surface. In a 
typical track following technique, the read/write electronics follow the 
tracks via servo sectors embedded at regular intervals around the track. 
In the case of high track density disks, the tracks are pre-recorded on the 
disk surface in a factory environment before the disk is suitable for use 
in a disk drive. Each blank disk is prepared for use by a device commonly 
referred to as a "servowriter." The servowriter is a machine dedicated to 
embedding servo signals into the disk's surface. After the servowriter has 
recorded the servo information in the servo sectors, the disk is checked 
for quality (e.g., by verifying the accuracy of the servo information). In 
some instances, for example where the disks are used in removable media 
drives, the verification process occurs at a separate time and place from 
the servowriting process at a device sometimes referred to as a verifier. 
Often, the servowriter and the verifier need the same data with regard to a 
particular disk. One particularly important example is the identification 
of the servowriter used to format a disk. This information is readily 
available at the time of the disk format. However, after the disk is 
removed from the servowriter and moved to a different location, the 
identity of the formatting servowriter may not be readily apparent. This 
identity becomes significant because, at times, a defective or poorly 
calibrated servowriter will introduce errors into the formatting process. 
Unfortunately, in the case of removable media disks, the errors may not be 
discovered until the disks are checked by the verifier. Tracking the 
servowriter is difficult because disks are prepared by numerous 
servowriters. Moreover, those servowriters may be located at a number of 
different locations. Nevertheless, to ensure maximum disk quality, it is 
important to be able to trace each disk back to the servowriter that 
formatted it. In this way, a servowriter that formats poorly can be 
discovered and corrected. If, for example, a single servowriter is 
responsible for introducing the majority of bad disks, that servowriter 
must be identified and corrected. 
Some disk manufacturers have used bar codes to trace the disks back to the 
servowriters and to provide other disk specific information. However, this 
requires some means for affixing a bar code to the disk, requiring an 
additional layer of expense and complexity. For example, attaching a bar 
code will add to the cost of producing each disk, or expensive equipment 
may be needed to properly track the disks. Moreover, an additional bar 
code scanning step may be required at the verifier. 
An additional example of data needed by both the verifier and the 
servowriter is media type. A variety of vendors may supply media readable 
by the same disk drive. Significantly, each of those media may have 
different characteristics that the verifier, and eventually a user's 
drive, should recognize. This media type information is also needed by the 
servowriter during the format process. Applicants have recognized that 
entering the data once, at the servowriter, and passing the data to the 
verifier would lead to fewer errors and higher quality. 
For the foregoing reasons, applicants have recognized that a method of 
efficiently passing data between a servowriter and a verifier would 
translate into substantial cost savings when aggregated over the large 
volume of disks produced and cut down on errors caused by redundant data 
entry. Consequently, there is a long-felt need for a method of efficiently 
transferring disk specific information from a servowriter to a verifier or 
other devices, such as disk drives. 
SUMMARY OF THE INVENTION 
The present invention meets the needs above by providing a method of 
recording the disk specific data (hereinafter "operational data") on each 
disk during the servowriter process and retrieving that information during 
verification. According to a presently preferred method of accomplishing 
that recordation and retrieval, a blank magnetic disk is formatted at a 
first station, e.g., a servowriter. While at the first station, an 
electromagnetic signal indicative of the operational data to be passed is 
embedded into the magnetic surface of the disks. The disk is then 
transported to a second station, e.g., a verifier. While the disk remains 
at the second station, the electromagnetic signal indicative of the 
operational data to be passed is retrieved off of the disk surface. 
In a presently preferred embodiment, the operational data is embedded in a 
guard band track. Preferably, the operational data is inserted into a grey 
code field in the guardband track. 
In a further aspect of the present invention, it is necessary to record the 
operational data in a more accessible location on the disk. Accordingly, 
in some instances, after the disk is transported to the second station, 
the operational data is moved to a second location on the disk, for 
example, the Z-track. 
According to another aspect of the present invention, the operational data 
comprises a station identifier indicative of the formatting servowriter. 
Thus, a blank disk is initially formatted on a servowriter, wherein a 
servowriter station identifier is recorded on the disk. Thereafter, the 
disk is verified on a verifier. The verifier reads the servowriter station 
identifier and uses that identifier to trace the performance of each 
servowriter. As such, for each disk that passes verification for a 
particular servowriter, a servowriter quality value, maintained for each 
servowriter, is increased. On the other hand, for each disk that fails 
verification, the corresponding servowriter quality value is decreased. 
These servowriter quality values can be used to track the servowriter 
quality over time and to flag a servowriter that consistently produces a 
high failure rate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
According to a presently preferred embodiment, a method for recording 
information on disks during the servowriting process and recovering that 
information during the verification process will now be described with 
reference to the FIGURES. It will be appreciated by those of ordinary 
skill in the art that the description given herein with respect to those 
FIGURES is for exemplary purposes only and is not intended in any way to 
limit the scope of the invention. For example, during the description of 
the preferred embodiment of the track layout, the number of tracks per 
disk, sectors per track and the like are used to illustrate the invention. 
However, such examples are merely for the purpose of clearly describing 
the method of the present invention and are not intended to limit the 
invention. Moreover, example applications are used throughout the 
description wherein the present invention is employed in conjunction with 
a particular disk drive system. That disk drive system application is not 
intended to limit the invention, as the invention is equally applicable to 
other systems. 
Referring to the FIGURES, FIG. 1 depicts a magnetic disk 10 for use in a 
disk drive system (not shown) wherein the present invention may be 
employed. The magnetic disk 10 shown may be one of several different 
types. For example, the present invention may be employed with a magnetic 
disk 10 for a ZIP drive or JAZ drive cartridge, both of which are 
manufactured by IOMEGA corporation, the assignee of the present invention. 
In order for the disk drive system to be able to access the magnetic disk 
10 and read from and write to the disk 10, the disk 10 must be formatted. 
In particular, a number of concentric tracks 11 must be defined over the 
surface of the disk 10. These tracks 11 are defined by the use of servo 
sectors 16. Each track 11 has a fixed number of servo sectors 16. A JAZ 
disk, for example, has servo sectors 16 sixty times per track 11 or every 
six degrees. Thereafter, when the disk 10 is used by a disk drive, the 
disk drive read/write electronics can read the servo sectors 16 and use 
that information to precisely follow the tracks 11 via a servo-loop. 
Other information must also be written to the disk 10 before it can be used 
in a disk drive. For example, the disk 10 must be subdivided into good 
sectors and tracks and bad sectors and tracks, i.e., those sectors and 
tracks that cannot be reliably used during operation, must be located and 
flagged. In the case of ZIP and JAZ disk cartridges, this information is 
placed onto a special track called the Z-track. Additionally, the disk 10 
includes guard band tracks 12 at the innermost 12b and outermost tracks 
12a. In general, these guard band tracks 12 are the same as all of the 
other tracks 11 on the disk. However, the disk drive electronics can 
determine whether a particular track 11 is part of the guard band 12 by 
the greycode number assigned to the track 11. In this manner, these guard 
band tracks 12 protect the disk drive read/write subsystem from traveling 
too far in or too far out during operation. 
In the case of ZIP and JAZ drive disks, as with many types of removable 
media disk cartridges, the format process is performed in two major steps. 
As shown in FIG. 1A, the first step in the format process is performed by 
a servowriter 50. The servowriter 50 is a finely calibrated formatting 
device that places servo sectors 16 at precise intervals on the surface of 
the disk 10. The major components of a servowriter 50 comprise a spindle 
51 for holding a disk 10 and spinning it up to operational speed; a 
read/write head 52 for writing and reading servo information to and from 
the disk 10; an arm 54 for moving the head 52 across the disk surface; an 
actuator 55 for controlling movement of the arm 54; a controller 58 for 
executing and controlling the servowriting process; and read/write 
electronics 56 for translating the electromagnetic signals of the disk 
surface to and from a digital format that is understood by the controller 
58. Additionally, the servowriter 50 comprises an input device, such as a 
keyboard, so that a servowriter operator can input information to control 
the servowriter process. Skilled artisans will appreciate that the 
servowriter 50 used to practice the present invention can be one of many 
commercially available units, such as Phase Metric/Helios MS 5000, 
appropriately modified to accept a particular variety of disk 10. 
After the disks are formatted with the servowriter 50, they are transported 
to a verifier 60 as indicated by dashed line 70 to undergo a verification 
step. The verifier 60 checks each disk 10 by writing data to the disk 10 
and reading the data back. In the presently preferred embodiment, the 
verifier 60 is simply a removable media disk drive, e.g., a ZIP or JAZ 
drive. The drives are modified to have special software designed to 
exercise the disk 10 by writing test data to it and reading the test data 
back from it. The major components of the verifier 60 are presented in 
block diagram form in FIG. 1A. Essentially, the verifier 60 comprises a 
controller 68 that controls the verification process that is executed on 
the verifier 68; read/write electronics 66 for translating data to and 
from the magnetic signals embedded in the disk surface; a read/write head 
62 for reading and writing magnetic signals to or from the disk surface; 
an arm 64 for suspending and moving the read/write head 62 on the disk 
surface; an actuator 65 for moving the arm 64 in response to commands from 
the read write electronics 66; and a spindle 61 for rotating the disk 10 
at operational speed. During the verification process, the format process 
performed by the servowriter 50 is checked and any sectors or tracks that 
cannot be read from or written to are flagged. 
Significantly, as indicated by the dashed line 70 in FIG. 1A, the 
servowriter process and the verifier process occur at different stations 
50, 60. Moreover, those stations may be at geographically separate 
locations. As a result, information available at the time of the 
servowriting process, such as media type, servowriter station and the 
like, will have to follow the disks 10 between stations. Furthermore, any 
errors that occur at the verifier 60 must be traced back to the 
servowriter 50 so that servowriter 50 induced errors can be corrected. 
Consequently, each disk 10 must be tagged with a variety of information so 
that the disks 10 can be identified throughout the format process and, 
perhaps, throughout its useful life. 
According to an aspect of the present invention, operational data for each 
disk 10 is inserted onto the disks 10 during the servowriter process by 
the servowriter 50. Thereafter, the verifier 60 recovers the operational 
data written onto the disk by the servowriter 50. According to a presently 
preferred embodiment of the present invention and as will be described 
more fully below, the servowriter 50 embeds the operational data in the 
servo sectors 16 of the guard band tracks 12. Thereafter, when the 
operational data is recovered by the verifier 60, the information may be 
moved to a data sector 17 for more permanent storage, as different 
applications of the present invention may require. 
Referring now to FIG. 2, an exploded view of a portion of the tracks 11 of 
the inner guard band 12b is shown. The tracks 11 of the guard band, just 
as normal tracks 11, have servo sectors 16 distributed around the tracks 
11 at predefined intervals. As shown in detail in the exploded servo 
sector view 16b each servo sector 16 is comprised of an automatic gain 
control (AGC) 22, overhead pad 24, greycode 26 and norm/quad fields 28. 
Because conventional servowriter read/write electronics operate at a much 
lower speed than the read/writer electronics of verifiers (i.e., the 
servowriters write low frequency information), servowriters 50 may not be 
capable of writing data in the conventional data sectors 17 of the disk 
10. However, the servowriter 50 is capable of writing lower frequency 
information in the servo sectors 16. Importantly, that information is 
readable by the verifier 60. Thus, according to a presently preferred 
embodiment of the present invention, the servowriter 50 writes data to be 
recovered by the verifier 60 into the servo sectors 16 of the disk 10. As 
will be described in detail below, in one example application, the 
information replaces several of the greycodes 26 in the tracks of the 
guard band of the disk 10. 
Note, however, that the present invention relates to the broad concept of a 
servowriter 50 writing operational data in the low frequency servo sectors 
16 of a disk 10 and recovering that operational data at the verifier 60. 
In this way, information readily available at the servowriter 50 does not 
have to separately follow each disk 10; rather, the information is 
embedded directly onto the disk 10, and as such automatically follows the 
disk 10 to the verifier 60. Those skilled in the art will recognize that 
many variations are possible to this fundamental concept. For example, the 
information could be written to the greycodes 26 as well as other servo 
sector 16 fields. Alternatively, a data area on the disk 10 could be used 
and the drive could be modified to read the appropriate frequency. 
Moreover, numerous applications for the transferred operational data are 
possible. As an example application, servowriter station identifiers could 
be written to each disk 10 and used to monitor the quality of each 
servowriter 50. 
Referring now to FIG. 3, the process of recording operational data to disks 
10 at the servowriter 50 is depicted. The process begins by mounting a 
disk 10 on the servowriter 50, spinning the disk 10 up to operational RPMs 
and loading the heads 52 onto the disk surface (step 102). After the heads 
52 are loaded onto the disk surface, they begin to move across the surface 
writing tracks 11 via servo sectors 16 and embedding greycodes 26 as track 
identifiers within each servo sector 16 of each track 11. The heads 52 
continue this process moving across the entire disk surface until all the 
tracks 11 are written. Since the greycode 26 is the track identifier, it 
is incremented for each successive track 11. 
Each servo sector 16 contains a grey code field 26. Conventionally, this 
greycode field 26 contains the track number. As such, during the operation 
of the disk drive, the grey code is used to locate a track 11 when data 
from a particular track 11 is requested and is used to insure that the 
read/write heads remain on the proper track 11. However, within the guard 
band 12 the tracks 11 are not used during the normal operation of the disk 
drive. Thus, this guard band 12 greycode information can be modified with 
no potential impact on the operation of the drive. Accordingly, during the 
servowriter process, the operational data is inserted into a selected 
group of the greycode fields 26 within the guard band 12. 
According to a preferred embodiment of the invention, when the tracks 11 of 
the guard band 12 are reached, some of the greycodes are written with the 
operational data in place of the normal greycode. Hence as depicted in 
FIG. 3, the servowriter process determines if the current track 11 is one 
of the tracks 11 to receive a special greycode (i.e. the operational data) 
(step 104). If not, the servowriter process continues normally, inserting 
servo sectors 16 with greycodes representative of the track number (step 
106). On the other hand, if this is a special greycode track, e.g., within 
the guard band 12, then the operational data is inserted in the servo 
sector 16 in place of a normal greycode (step 108). The next one-third of 
the track (i.e., 120 degrees) is written with the normal greycode inserted 
into the greycode field 26 (step 110). This process continues until the 
track 11 is completed (step 112). Consequently, when each special greycode 
track is completed, it will have three servo sectors 16, spaced apart 120 
degrees around the track, each of which servo sector 16 contains 
operational data rather than the greycode. By contrast, the remaining 
servo sectors 16 for the same track 11 will contain normal greycodes. This 
servowriting process continues until all tracks 11 have been formatted 
(step 114). When the process is completed the heads are unloaded, the 
spindle stops and the disk 10 is released (step 116). The formatted disks 
10 are then transported to a verifier 60 where they are quality tested. 
After the disks 10 arrive at the verifier 60, the operational data is 
extracted from the special greycode fields 26. In some instances, the 
operational data will also be saved as data on a different location on the 
disk (i.e. the tracks known as the Z-tracks). To begin the verification 
process the disks 10 are inserted into the verifier 60. 
Referring to FIG. 4, a flow chart of the operational data extraction 
portion of the verification process is presented. The process begins when 
a disk is inserted into a verifier 60. Thereafter, the verifier 60 is 
commanded to seek to the inner guard band tracks 12b (step 1002), and a 
count is initialized to zero (step 1004). Starting with the first track 11 
of the inner guard band 12b, all greycodes are extracted (step 1006). In a 
presently preferred embodiment, the operational data to be recovered is 
repeated in three greycode fields 26 within the same track 11. As a 
result, those three greycode fields 26 will not match the current guard 
band track number. Thus, to locate the special greycodes, each greycode is 
checked against the current track number (step 1008). If the greycode does 
not match the current track number, then the greycode is saved as a 
special greycode (i.e., it is possibly operational data) (step 1010), and 
the count is incremented (step 1012). If this is the last expected special 
greycode, e.g., the third one, then the check is finished (step 1014-1016) 
and the operational data has been recovered. Otherwise, this is not the 
last special greycode, and the checking of greycodes continues (step 
1014-1018). After the three special greycodes are found, they are compared 
against one another as an error check. That is, the greycodes found that 
do not match the current track number should match each other. If there is 
a mismatch between the special greycodes, then an error has occurred, and 
the operational data cannot be recovered from this track 11 (steps 
1020-1022). 
If the greycode has not been recovered from the preceding track 11 and the 
track number is still within the range of the guard band 12b, an attempt 
is made to retrieve operational data from the next available guard band 
track 11 (steps 1024-1026), and the steps above are repeated. If the next 
track 11 is beyond the range of the guard band 12b, a failure condition 
occurs (steps 1024-1028). In such a failure case, the operational data 
cannot be recovered. 
This process describes how a single piece of operational data is inserted 
at the servowriter 50 and recovered at the verifier 60. Obviously, this 
process could be slightly modified to insert and recover multiple pieces 
of operational data. 
In a particular application of the present invention, the operational data 
is used to track and control the quality of the servowriter 50. In such a 
case, the verifier 60 must know the identify of the servowriter 50 that 
formatted each disk 10. In a typical disk format production arrangement, 
multiple servowriters 50 simultaneously format batches of disks 10. Those 
disks are then transported to multiple verifiers 60. In such a production 
environment, it is vital to track the quality of the servowriters 50 and 
to identify those servowriters 50 that are performing inadequately. As 
such, each disk 10 is tagged during the servowriting process with an 
identification of the servowriter that formatted that disk. As previously 
indicated, this servowriter identifier (i.e., the operational data) will 
be recorded in place of the greycode field 26 within several servo sectors 
16. Thereafter, the servowriter identifier mark can be recovered at the 
verifier 60 during the verification process. 
When the servowriter 50 has been identified it is written to the disk 10 as 
data on the Z-tracks. Moreover, the servowriter identifier can be save in 
a database file so that servowriter confidence and yields can be tracked. 
Faulty servowriters are then determined based on a confidence value. In 
particular, if a particular servowriter confidence value falls below a 
threshold, the servowriter 50 is shut down. The servowriter confidence 
value is determined by the number of consecutive passes and fails for a 
particular servowriter. 
In the presently preferred embodiment, the confidence value is reduced by 
10% for each fail and increased by 5% for each pass. Thus, a few failures 
rapidly reduced the confidence value. By setting this value accordingly, a 
servowriter's 50 quality can be controlled. 
A second application of the present invention transfers media type between 
the servowriter and the verifier. The blank magnetic disks may be produced 
by a variety of manufacturers. As a result, disk characteristics may vary. 
In order for the verifier, and eventually the user's drive, to optimize 
performance, the media type is determined and the verifier, and the user's 
drive, is adjusted. The media type is determined during the servowriter 
stage, when the media first arrives from the media vendors. Accordingly, 
when the servowriter formats a disk, media type is inserted onto the disk 
as the operational data (i.e., via the greycode). Thereafter, when the 
disk is verified, the media type is extracted, used by the verifier and 
then copied to the Z-track for use by a user's drive. 
Those skilled in the art will readily appreciate that many modifications to 
the invention are possible within the scope of the invention. For example, 
the operational data could merely contain a unique disk identifier. By 
then connecting the servowriters and verifiers together over a network, 
data for each disk can be stored in a database and retrieved by the 
servowriters 50 and verifiers 60. Moreover, the techniques described 
herein are not limited to tracing servowriters during the disk format 
process. Other uses for the methods disclosed are possible. For example, 
the disks could be traced during their useful life and high in-use failure 
rates identified. Accordingly, the scope of the invention is not intended 
to be limited by the preferred embodiment described above but only by the 
appended claims.