Abstract:
Approaches for a testing device for selecting a discrete track media (DTM) format for use with a particular head of a hard-disk drive (HDD). The testing device comprises a continuous magnetic-recording disk, rotatably mounted on a spindle, which stores data using a continuous media format. The testing device also comprises a testing module configured to simulate reading data, stored using a discrete track media (DTM) format, from the continuous magnetic-recording medium. Advantageously, testing time and cost is reduced as both discrete track media (DTM) disks and expensive discrete track media (DTM) recording testing hardware are not required to select the optimal a discrete track media (DTM) format for use with a particular head of a hard-disk drive (HDD). In addition, embodiments may be used to optimize features of the tracks of the DTM disk, such as the land to groove ratio.

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention generally relate to the selection of a discrete track media (DTM) format for use with a particular head of a hard-disk drive (HDD). 
     BACKGROUND OF THE INVENTION 
     A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator. 
     A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension&#39;s force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface. 
     The performance capabilities of a read/write head can vary significantly from head to head. This is so because several hundred or more processes may be involved in the manufacturing process of a head, which results in manufactured heads having a wide distribution of physical and performance characteristics. As performance of a head increases, the width of the track to which the head can write decreases. Thus, better performing heads can be used with narrower tracks. 
     Two common types of digital storage media are discrete track media (DTM) and continuous media. In discrete track media (DTM), tracks are pre-patterned with magnetic tracks (lands) separated by non-magnetic grooves. On the other hand, in continuous media, tracks are not pre-patterned and the surface of the disk does not contain any non-magnetic grooves. 
     When continuous media is used, the track format may be adapted during operation to reflect the particular performance characteristics (such as the signal to noise ratio) of the particular head used in the HDD. However, in discrete track media, tracks are pre-patterned on the magnetic-recording disk and the area between each track is constructed to be non-magnetic. Consequently, in discrete track media (DTM), the ability to customize the track format during operation is lost. 
     To accommodate the wide distribution of performance characteristics across read/write heads, multiple templates may be designed for a DTM magnetic-recording disk. Each template specifies a different design for physically laying out tracks on the disk. For example, different templates may specify different track pitches. When manufacturing a particular HDD employing a DTM disk, the performance capabilities of the actual head to be used in the HDD are evaluated. Once the performance capabilities of the head are known, the template having a track format that is best suited for the particular head being used in the HDD may be selected. After selecting the template that is best suited for the actual head to be used, the magnetic-recording disk may be pre-patterned with tracks according to the selected template. 
     SUMMARY OF THE INVENTION 
     One approach for selecting the track format for a given head is to test the head on multiple DTM magnetic-recording disks, each of which having a different track format, to identify on which track format the head performs best. Unfortunately, this approach increases testing time and complexity. Also, this approach is undesirable because it increases the turn-around time in product development, e.g., if there is any change in a DTM track format, one has to wait for the DTM disk having the new format to be fabricated before a heads can be matched to DTM track formats. 
     Embodiments of the invention provide for an improved approach for determining which discrete track media (DTM) track format is best suited for a particular head by simulating discrete track media (DTM) recording conditions using continuous media. In an embodiment, a testing device for selecting a discrete track media (DTM) format for use with a particular head of a hard-disk drive (HDD) comprises not a disk conforming to a DTM format, but instead, comprises a continuous magnetic-recording disk rotatably mounted on a spindle. The continuous magnetic-recording disk stores data using a continuous media format. The testing device of an embodiment comprises a testing module that is configured to simulate reading data, stored using a particular discrete track media (DTM) format, from the continuous magnetic-recording medium. Multiple DTM track densities/formats may be simulated by the testing device using a single continuous media disk. 
     Advantageously, using embodiments of the invention, testing time and cost is reduced as discrete track media (DTM) disks and expensive discrete track media (DTM) recording testing hardware are not required. In addition, embodiments may be used to optimize features of the tracks of the DTM disk, such as the land to groove ratio. 
     Embodiments discussed in the Summary of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a block diagram of a testing device employing a continuous media disk according to an embodiment of the invention; 
         FIG. 2  is a plan view of an HDD according to an embodiment of the invention; 
         FIG. 3  is a plan view of a head-arm-assembly (HAA) according to an embodiment of the invention; 
         FIG. 4  is a flowchart illustrating the functional steps of determining which discrete track media (DTM) track format is best suited for a particular head by simulating discrete track media (DTM) recording conditions using a continuous media according to an embodiment of the invention; 
         FIG. 5  is an illustration of writing to lands and grooves using square waves of certain frequencies according to an embodiment of the invention; 
         FIG. 6  is a graph of track averaged amplitude (TAA) profile data according to an embodiment of the invention; 
         FIG. 7  is a graph depicting a calculated SNR profile according to an embodiment of the invention; and 
         FIG. 8  is an illustration of evaluating which track pitch is best suited for a given head according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Approaches for selecting of a particular discrete track media (DTM) format for use with a particular head of a hard-disk drive (HDD) are described. Embodiments of the invention employ a testing device that simulates a disk pre-patterned in one or more discrete track media (DTM) formats using a magnetic-recording disk having tracks in the continuous media format. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
     Physical Description of Illustrative Embodiments of the Invention 
     Embodiments of the invention may be embodied in a standard testing device for assessing the capabilities of a read/write head. Advantageously, testing devices according to embodiments use continuous media disks instead of discrete track media (DTM) disks. 
       FIG. 1  is a block diagram of testing device  100  employing continuous media disk  110  according to an embodiment of the invention. Testing device  100  may be used to select a particular template  122  from plurality of templates  120  for use with a particular head  102 . Each template in plurality of templates  122  identifies a track format for use on a discrete track media (DTM). Testing device  100  may be implemented using a standard testing device for evaluating performance capabilities of heads. Testing device  100  is configured to perform the steps discussed below with reference to  FIG. 4 . In an embodiment, a standard testing device which may be modified to perform the steps of  FIG. 4  is described in U.S. Pat. No. 7,525,307, which is incorporated by reference for all purposes as if fully set forth herein. 
     Physical Description of Illustrative Hard-Disk Drives (HDDs) 
     For purposes of providing a concrete example of contexts in which read/write heads, continuous media disks, and discrete media track (DTM) disks operate, the operation of a hard-disk drive (HDD) employing a magnetic-recording disk shall now be described; however, embodiments of the invention may be used in any type of storage media employing rotating platters or disks. 
     In accordance with an embodiment of the invention, a plan view of a HDD  200  is shown in  FIG. 2 .  FIG. 2  illustrates the functional arrangement of components of the HDD including a slider  210   b  that includes a magnetic-recording head  210   a . The HDD  200  includes at least one head gimbal assembly (HGA)  210  including the head  210   a , a lead suspension  210   c  attached to the head  210   a , and a load beam  210   d  attached to the slider  210   b , which includes the head  210   a  at a distal end of the slider  210   b ; the slider  210   b  is attached at the distal end of the load beam  210   d  to a gimbal portion of the load beam  210   d . The HDD  200  also includes at least one magnetic-recording disk  220  rotatably mounted on a spindle  224  and a drive motor (not shown) attached to the spindle  224  for rotating the disk  220 . The head  210   a  includes a write element and a read element for respectively writing and reading information stored on the disk  220  of the HDD  200 . The disk  220  or a plurality (not shown) of disks may be affixed to the spindle  224  with a disk clamp  228 . The HDD  200  further includes an arm  232  attached to the HGA  210 , a carriage  234 , a voice-coil motor (VCM) that includes an armature  236  including a voice coil  240  attached to the carriage  234 ; and a stator  244  including a voice-coil magnet (not shown); the armature  236  of the VCM is attached to the carriage  234  and is configured to move the arm  232  and the HGA  210  to access portions of the disk  220  being mounted on a pivot-shaft  248  with an interposed pivot-bearing assembly  252 . 
     With further reference to  FIG. 2 , in accordance with an embodiment of the present invention, electrical signals, for example, current to the voice coil  240  of the VCM, write signal to and read signal from the PMR head  210   a , are provided by a flexible cable  256 . Interconnection between the flexible cable  256  and the head  210   a  may be provided by an arm-electronics (AE) module  260 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The flexible cable  256  is coupled to an electrical-connector block  264 , which provides electrical communication through electrical feedthroughs (not shown) provided by an HDD housing  268 . The HDD housing  268 , also referred to as a casting, depending upon whether the HDD housing is cast, in conjunction with an HDD cover (not shown) provides a sealed, protective enclosure for the information storage components of the HDD  200 . 
     With further reference to  FIG. 2 , in accordance with an embodiment of the present invention, other electronic components (not shown), including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  240  of the VCM and the head  210   a  of the HGA  210 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  224  which is in turn transmitted to the disk  220  that is affixed to the spindle  224  by the disk clamp  228 ; as a result, the disk  220  spins in a direction  272 . The spinning disk  220  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  210   b  rides so that the slider  210   b  flies above the surface of the disk  220  without making contact with a thin magnetic-recording medium of the disk  220  in which information is recorded. The electrical signal provided to the voice coil  240  of the VCM enables the head  210   a  of the HGA  210  to access a track  276  on which information is recorded. Thus, the armature  236  of the VCM swings through an arc  280  which enables the HGA  210  attached to the armature  236  by the arm  232  to access various tracks on the disk  220 . Information is stored on the disk  220  in a plurality of concentric tracks (not shown) arranged in sectors on the disk  220 , for example, sector  284 . Correspondingly, each track is composed of a plurality of sectored track portions, for example, sectored track portion  288 . Each sectored track portion  288  is composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, information that identifies the track  276 , and error correction code information. In accessing the track  276 , the read element of the head  210   a  of the HGA  210  reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  240  of the VCM, enabling the head  210   a  to follow the track  276 . Upon finding the track  276  and identifying a particular sectored track portion  288 , the head  210   a  either reads data from the track  276  or writes data to the track  276  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
     Embodiments of the invention also encompass HDD  200  that includes the HGA  210 , the disk  220  rotatably mounted on the spindle  224 , the arm  232  attached to the HGA  210  including the slider  210   b  including the head  210   a.    
     With reference now to  FIG. 3 , in accordance with an embodiment of the present invention, a plan view of a head-arm-assembly (HAA) including the HGA  210  is shown.  FIG. 2  illustrates the functional arrangement of the HAA with respect to the HGA  210 . The HAA includes the arm  232  and HGA  210  including the slider  210   b  including the head  210   a . The HAA is attached at the arm  232  to the carriage  234 . In the case of an HDD having multiple disks, or platters as disks are sometimes referred to in the art, the carriage  234  is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. As shown in  FIG. 4 , the armature  236  of the VCM is attached to the carriage  234  and the voice coil  240  is attached to the armature  236 . The AE  260  may be attached to the carriage  234  as shown. The carriage  234  is mounted on the pivot-shaft  248  with the interposed pivot-bearing assembly  252 . 
     Selecting a DTM Template Using an Embodiment 
     Embodiments of the invention perform analysis on a head to identify a track width that should be used with the head by considering the signal to noise ratio as a function of read back location. Initially, one frequency is used to write to a portion of a continuous media that simulates a data track of a discrete track media, and a different frequency is used to write to another portion of the continuous media that simulates the grooves of the discrete track media. A filter is then used to read back the signal written to the simulated data track. The best place to read a signal from a track is from the center of the track because as the read head moves from the center of the track, more noise from adjacent tracks is introduced into the readback signal. By measuring the off-track capability (OTC) of the head (explained and illustrated in more detail below), the amount that the track can be “squeezed,” or narrowed, can be calculated. The higher the OTC of a head, the better the performance of the head and the narrower the track that can be supported. 
       FIG. 4  is a flowchart illustrating the functional steps of determining which discrete track media (DTM) track format is best suited for a particular head by simulating discrete track media (DTM) recording conditions using a continuous media according to an embodiment of the invention. In an embodiment, each step of  FIG. 4  may be performed by testing device  100  of  FIG. 1 . 
     In step  410 , testing device  100  writes tracks to continuous media disk  110  in a manner that simulates how data is written on a discrete track media (DTM) disk. On a discrete track media (DTM) disk, data is stored on areas of the disk having an exposed layer of magnetic material (referred to as lands) separated by areas lacking an exposed layer of magnetic material (referred to as grooves). A land corresponds to a track on which data is written, and a groove corresponds to the area between tracks. By convention, the particular land that is currently being written to is referred to as the “data land,” while the lands which are immediately adjacent to the data land are referred to as the adjacent lands. An adjacent land which is closer to the inner diameter of the disk may be identified as the “adjacent land (ID)” and the adjacent land which is closer to the outer diameter of the disk may be identified as the “adjacent land (OD).” 
     One approach for performing step  410  is shown in  FIG. 5 . In the embodiment illustrated in  FIG. 5 , each land and groove is written to using a square wave of a certain frequency. Specifically, data land  502  is written to using square wave frequency f 1 , adjacent lands  504  and  506  are written to using square wave frequency f 2 , and grooves  508  and  510  are written to using square wave f 3 . Writing to lands using a different frequency than to grooves is advantageous because only signals written to lands are intended to be read back; signals written to grooves can be filtered out to simulate the effect of the non-magnetic grooves of a DTM disk. Only signals written to data land  502  and adjacent lands  504  and  506  are intended to be read back by embodiments. Signals written to grooves  508  and  510  are not intended to be read back to simulate the effect of non-magnetic grooves in a DTM format. 
     Note that the width of a land L, such as data land  502 , adjacent land  504 , or adjacent land  506 , may be varied by trimming, a technique well known to those in the art. Also, the width of the grooves G can be varied by adjusting the distance between the data land and the adjacent lands. 
     After data is written to continuous disk  110  in a manner that simulates how data is stored on a DTM disk, in step  420 , testing device  100  reads amplitude profiles for tracks on continuous media disk  110 . Testing device  100  may read the amplitude profiles for the data land and adjacent lands (at ID and OD) written on disk  110  using narrow band or overwrite filters at various off-track positions. In this way, only the signal written to data land  502  and adjacent lands  504  and  506  are read back; signals written to grooves  508  and  510  are not read back. 
       FIG. 6  is a graph of track averaged amplitude (TAA) profile data obtained in step  420  according to an embodiment of the invention. A TAA profile is data that describes the amplitude of a signal read from locations on a track. As shown in  FIG. 6 , the amplitude of the signal written to the data land is the highest in the center of the data land, as would be expected. The amplitude of the signal written to the data land decreases with distance from the center of the data land. 
     In step  430 , testing device  100  calculates a signal to noise profile (hereinafter a “SNR profile”) and an off-track capability (OTC) for the SNR profile. In an embodiment, the SNR profile may be determined using an equation, such as: 
               S   ⁢           ⁢   N   ⁢           ⁢   R     =     10   ⁢           ⁢     log   10     ⁢       T   ⁢           ⁢   A   ⁢           ⁢     A   Data   2           α   ⁢           ⁢   T   ⁢           ⁢   A   ⁢           ⁢     A   Data   2       +     T   ⁢           ⁢   A   ⁢           ⁢     A   OD   2       +     T   ⁢           ⁢   A   ⁢           ⁢     A   ID   2                   
In the above equation, the parameter a may be determined by measuring the integrated media signal-to-noise ratio (SNRm), and the parameter a may be calculated using the relation SNRm=−10 log 10 α. TAA Data , TAA ID , and TAA OD  are read-back amplitudes from the data land  502 , adjacent land  506 , and adjacent land  504 , respectively.
 
       FIG. 7  is a graph depicting the SNR profile calculated in step  430  according to an embodiment of the invention. Once the SNR profile is obtained, testing device  100  may calculate the off-track capability (OTC) for the determined SNR profile. In an embodiment, the off-track capability (OTC) corresponds to the full width of the SNR profile at the given SNR level, as shown in  FIG. 7 . The wider the off-track capability (OTC), the narrower the track that is supported by the head. 
     In step  440 , testing device  100  determines if the off-track capability (OTC) for a particular head is sufficient to support a given DTM track format. According to one approach, testing device  100  may performing this step using by deriving a signal-to-noise ratio based 747 curve to determine if the OTC for the particular head is sufficient for a given track. A 747 curve in this context is a measure of OTC versus squeeze track pitch. This is different than how a 747 curve is typically used, as typically a 747 curve is based on a Bit Error Rate (BER). 
     In an embodiment, to determine if a given head can support a particular DTM track format, testing device  100  determines the squeeze track pitch at which the OTC is 15% of the squeeze track pitch. Then, testing device  100  determines whether the DTM track pitch lengths L+G (as illustrated in  FIG. 5 ) are equal to or greater than 110% of the squeeze track pitch previously obtained. If testing device  100  determines that the DTM track pitch lengths L+G (as illustrated in  FIG. 5 ) are equal to or greater than 110% of the squeeze track pitch previously obtained, then testing device  100  determines that the head can support the particular DTM track format; otherwise, testing device  100  determines the head cannot support the particular DTM track format. Note that the percentages in this embodiment may differ than those used in other embodiments, as other thresholds may be used by other embodiments as these particular percentages are merely illustrative of one embedment. 
     Non-Limiting Example of an Embodiment 
     In an embodiment, testing device  100  is used to test head  102  with various DTM track formats on a continuous media disk  110 . In the test, the DTM track pitches range from 3 to 10 μinch and the land width and groove width are equal. The magnetic core width of head  102  is 5 μinch. 
       FIG. 8  is an illustration of evaluating which track pitch is best suited for head  102  according to an embodiment of the invention.  FIG. 8  depicts 747 curves of simulated DTM media with various track pitches (L+G) for head  102 . As shown in  FIG. 8 , head  102  can support a DTM track pitch as small as 4 μinch. When comparing with recording using continuous media, the same head can achieve a track pitch of 4 μinch in DTM and 5.5 μinch track pitch in continuous media, which is a 37.5% increase in track density. 
     In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.