Abstract:
Embodiments of the present invention provide a magnetic disk drive system in which the write element leads the read element in the tangential direction of rotation of the magnetic disk. In addition, the servo sector information is preferably arranged such that information that is not needed for write operation is placed at the end of the servo sector. In this way, the servo read operation can be terminated sooner and the write operation can initiate sooner after going over the servo sector. The write element in a write operation writes data to the data sector of a track until an end of the data sector before reaching a front end of a servo sector following the end of the data sector. The read element reads information in the servo sector needed for the write operation. The write element starts writing data in a next data sector following the servo sector after the write element reaches the next data sector and after the read element has read all information in the servo sector needed for the write operation.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     NOT APPLICABLE 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to magnetic disk drive systems and, more particularly, to a magnetic disk drive system in which the write element leads the read element in the tangential direction of rotation of the magnetic disk. 
     A typical read/write head in a hard disk drive consists of a read element that leads a write element in the tangential direction of rotation of the magnetic disk. The read head goes over a particular part of the rotating disk before the write head. During customer write operation, the write process must terminate before the read head reaches the servo wedge leaving a gap equals to the length of the read to write head distance. The read element and the write element cannot both be operated at the same time due to magnetic and electrical noise and interaction. Moreover, an additional gap must be added to allow time for the disturbance to decay due to switching from write mode to read mode, known as write to read recovery. As seen in the read/write head  10  of  FIG. 1 , a read head  12  leads the write head  14  in the tangential direction  16  over the magnetic disk. In  FIG. 1A , the write head  14  has just gone over the previous servo wedge or servo identification (SID) region. As the head  10  moves across the data sector, the write head  14  must terminate at location  20  to allow time for the disturbance due to switching to decay (W/R recovery) and to leave a gap equal to the length of the read to write head distance (R/W separation), as seen in  FIG. 1B . See, e.g., U.S. Pat. Nos. 5,760,983 and 6,219,194, and U.S. Patent Publication No. 2005/0057837. The total gap represents a loss of area for write operation, and can typically be as much as 30-50% of the total servo overhead. The overall sequential data rate is reduced by the same amount due to this gap. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a magnetic disk drive system in which the write element leads the read element in the tangential direction of rotation of the magnetic disk. In addition, the servo wedge information is preferably arranged such that information that is not needed for write operation is placed at the end of the servo wedge. In this way, the servo read operation can be terminated sooner and the write operation can initiate sooner after going over the servo wedge. 
     In accordance with an aspect of the present invention, a disk drive comprises a disk including a plurality of tracks each having a plurality of data sectors spaced by servo sectors, the disk configured to rotate in a circumferential direction of the tracks; a magnetic head having a write element to write data to the tracks and a read element to read data from the tracks, the write element being disposed in front of the read element against the circumferential direction of rotation of the disk so that the write element goes over a location on a track before the read element; and a processor configured to control the write element of the magnetic head in a write operation to write data to the data sector of a track until an end of the data sector before reaching a front end of a servo sector following the end of the data sector, to control the read element of the magnetic head to read information in the servo sector needed for the write operation, and to control the write element to start writing data in a next data sector following the servo sector after the write element reaches the next data sector and after the read element has read all information in the servo sector needed for the write operation. 
     In some embodiments, the write element is separated from the read element by a read/write separation gap; a write to read recovery is needed for disturbance to decay due to switching from write mode to read mode before the read element starts reading information in the servo sector after the write element stops writing in the data sector; and the write to read recovery is equal to or smaller than the read/write separation gap to allow time for disturbance to decay due to switching from write mode to read mode so as to provide write to read recovery. The magnetic head is disposed at a skew angle with respect to a tangent of the track so that the read/write separation gap is disposed at the skew angle with the tangent of the track, and wherein the processor is configured to employ an adaptive formatting technique to account for effect of the skew angle in ensuring that the write to read recovery is equal to or smaller than the read/write separation gap. 
     In some embodiments, the write element is separated from the read element by a read/write separation gap; a write to read recovery is needed for disturbance to decay due to switching from write mode to read mode before the read element starts reading information in the servo sector after the write element stops writing in the data sector; the write to read recovery is larger than the read/write separation gap by a recovery difference; and the processor is configured to control the write element to stop writing before reaching the end of the data sector by a space from the end of the data sector which is equal to or larger than the recovery difference so as to allow time for disturbance to decay due to switching from write mode to read mode. The magnetic head is disposed at a skew angle with respect to a tangent of the track so that the read/write separation gap is disposed at the skew angle with respect to the tangent of the track, and wherein the processor is configured to employ an adaptive formatting technique to account for effect of the skew angle in comparing the read/write separation gap with the write to read recovery in controlling the write element to stop writing in the data sector to allow time for disturbance to decay due to switching from write mode to read mode. 
     In specific embodiments, servo information in the servo sector is arranged such that information that is not needed for write operation is placed at a back end region of the servo sector. The information that is not needed for write operation includes one or more of cylinder address bit(s), read repeatable runout field, and part of a fine position tracking signal not necessary for write operation. If the size of the back end region is equal to or larger than the read/write separation gap, and wherein the processor is configured to control the write element to start writing in the next data sector substantially immediately after going over the back end of the servo sector so as to eliminate delay due to the read/write separation gap. If the size of the back end region is smaller than the read/write separation gap, and wherein the processor is configured to control the write element to start writing in the next data sector substantially immediately after the read element enters the back end region so as to reduce delay due to the read/write separation gap by an amount equal to the size of the back end region. The magnetic head is disposed at a skew angle with respect to a tangent of the track so that the read/write separation gap is disposed at the skew angle with respect to the back end region of the servo sector, and wherein the processor is configured to employ an adaptive formatting technique to account for effect of the skew angle in comparing the read/write separation gap with the size of the back end region for controlling the write element to start writing in the next data sector. 
     Another aspect of the invention is directed to a method of performing a write operation for a disk drive which includes a disk including a plurality of tracks each having a plurality of data sectors spaced by servo sectors, the disk configured to rotate in a circumferential direction of the tracks; and a magnetic head having a write element to write data to the tracks and a read element to read data from the tracks, the write element being disposed in front of the read element against the circumferential direction of rotation of the disk so that the write element goes over a location on a track before the read element. The method comprises controlling the write element of the magnetic head in a write operation to write data to the data sector of a track until an end of the data sector before reaching a front end of a servo sector following the end of the data sector; controlling the read element of the magnetic head to read information in the servo sector needed for the write operation; and controlling the write element to start writing data in a next data sector following the servo sector after the write element reaches the next data sector and after the read element has read all information in the servo sector needed for the write operation. 
     Another aspect of the invention is directed to a computer readable storage medium including a computer code for operating a disk drive which includes a disk including a plurality of tracks each having a plurality of data sectors spaced by servo sectors, the disk configured to rotate in a circumferential direction of the tracks; and a magnetic head having a write element to write data to the tracks and a read element to read data from the tracks, the write element being disposed in front of the read element against the circumferential direction of rotation of the disk so that the write element goes over a location on a track before the read element. The computer code comprises code for controlling the write element of the magnetic head in a write operation to write data to the data sector of a track until an end of the data sector before reaching a front end of a servo sector following the end of the data sector; code for controlling the read element of the magnetic head to read information in the servo sector needed for the write operation; and code for controlling the write element to start writing data in a next data sector following the servo sector after the write element reaches the next data sector and after the read element has read all information in the servo sector needed for the write operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are simplified diagrams showing movement of a conventional read/write head in which the read element leads the write element to illustrate a gap that determines when to terminate the write process before the read head reaches the servo wedge. 
         FIG. 2A  is an exemplary simplified perspective view of a hard disk drive (HDD) that can be used as a data storage device within computing device according to an embodiment of the present invention. 
         FIG. 2B  is an exemplary simplified functional block diagram of the HDD according to an embodiment of the present invention. 
         FIG. 3  is a simplified diagram showing movement of a read/write head in which the write element leads the read element to illustrate the elimination or reduction of the gap required in the prior art according to an embodiment of the present invention. 
         FIGS. 4A-4C  are simplified diagrams showing one example of rearranging the servo sector information such that information that is not needed for write operation is placed at a back end region of the servo sector. 
         FIG. 5  is a simplified diagram showing the skew angle for a conventional magnetic head with the read element disposed before the write element. 
         FIG. 6  is a schematic diagram showing the physical arrangement of a rotary actuator of a hard disk drive in relationship to a hard disk. 
         FIG. 7  is a diagram of the physical arrangement of  FIG. 6  with the rotary actuator removed. 
         FIG. 8  is a schematic diagram showing the physical arrangement used for determining the angle of a read/write head with respect to a circumferential data track at a given radius. 
         FIG. 9  is a schematic diagram showing that the spacing loss decreases at the outer and inner diameters of a hard disk. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2A  shows is an exemplary simplified perspective view of a hard disk drive (HDD)  100  that may incorporate the read/write head of the present invention according to an embodiment of the present invention.  FIG. 2B  is an exemplary simplified functional block diagram of the HDD according to an embodiment of the present invention. As shown in  FIG. 2A , the HDD  100  includes a disk enclosure  200  having a top cover  103  installed to seal the open top of a box-shaped base  102 , which may be made, for instance, of an aluminum alloy. The top cover  103  is made, for instance, of stainless steel, and is fastened by fasteners to the base  102  with a sealing member (not shown), which is shaped like a rectangular frame. The disk enclosure  200  contains a spindle motor (not shown), which comprises, for instance, a hub-in, three-phase DC servo motor. The spindle motor imparts rotary drive to a magnetic disk  105 , which is a storage medium. One or more units of the magnetic disk  105  are installed in compliance with the storage capacity requirements for the HDD  100 . A card  300  is attached to the lower surface of base  102 . The card  300  carries a signal processing circuit, a drive circuit for spindle motor, and other components described later. 
     An actuator arm  106  is mounted within the disk enclosure  200 . The middle section of the actuator arm  106  is supported above the base  102  so that it can pivot on a pivot axis  107 . A composite magnetic head  108  is mounted on one end of the actuator arm  106 . A VCM (voice coil motor) coil  109  is mounted on the remaining end of the actuator arm  106 . The VCM coil  109  and a stator  110 , which is made of a permanent magnet and fastened to the disk enclosure  200 , constitute a VCM  111 . When a VCM current flows to the VCM coil  109 , the actuator arm  106  can move to a specified position over the magnetic disk  105 . This movement causes the composite magnetic head  108  to perform a seek operation. The magnetic disk  105  is driven to rotate around a spindle axis of the spindle motor. When HDD  100  does not operate, the magnetic disk  105  comes to a standstill. 
     As seen in  FIG. 2A , the composite magnetic head unit  108  may be a combination of an ILS (integrated lead suspension) (not shown), a read head  155 , which comprises a GMR (giant magnetoresistive) sensor, and a write head  154 , which comprises an induction-type converter. The read head  155  reads servo information when the head unit  108  reads data, writes data, or performs a seek operation. For a data read operation, the read head  155  also reads data between items of servo information. For a data write or data read, the actuator arm  106  pivots over the surface of the magnetic disk  105  during its rotation so that the composite magnetic head unit  108  performs a seek operation to scan for an arbitrary track on the magnetic disk  105 . In this instance, the ABS (air bearing surface) of composite magnetic head unit  108 , which faces the magnetic disk  105 , receives a lift force due to an air current generated between the ABS and the magnetic disk  105 . As a result, the composite magnetic head unit  108  constantly hovers a predetermined distance above the surface of the magnetic disk  105 . 
     The read head  155  and write head  154 , which constitute the composite magnetic head unit  108 , are electrically connected to the head IC  152 . The head IC  152  is mounted on a lateral surface of the pivot axis  107  of the actuator arm  106 . One end of a flex cable  113  is connected to the head IC  152  to permit data exchange with the card  300 . A connector  114  is attached to the remaining end of the flex cable  113  for connecting to the card  300 . A temperature sensor  115  may be mounted on the upper surface of the connector  114  to measure the temperature inside the disk enclosure  200  (the ambient temperature for the magnetic disk  105 ). 
     The card  300  includes electronic circuits shown in  FIG. 2B , which control the operation of the actuator arm  106  and perform data read/write operations in relation to the magnetic disk  105 . The card  300  controls the rotation of the magnetic disk  105  through a spindle/VCM driver  159  and drives the VCM coil  109  to control the seek operation of the actuator arm  106 . 
     The HDD controller  150  transfers data between an external host (not shown) and the magnetic disk  105 , generates a position error signal (PES) from servo data, and transmits the positional information about the composite magnetic head  108  to a read/write controller  151  and a microprocessor  158 . In accordance with the control information from the microprocessor  158 , the spindle/VCM driver  159  drives the VCM coil  109  to position the composite magnetic head  108  on the specified track. The positioning of the magnetic head unit  108  is determined by an IC position converter  156  in response to a signal from the magnetic head unit  108 . The microprocessor  158  further interprets a command that is transmitted from an external host (not shown) through the HDD controller  150 , and instructs the HDD controller  150  to perform a data read/write operation in relation to an address specified by the command. In accordance with the positional information about the composite magnetic head  108 , which is generated by the HDD controller  150 , the microprocessor  158  also transmits control information to the spindle/VCM driver  159  for the purpose of performing a seek operation to position composite magnetic head  108  on a specified track. 
       FIG. 3  shows a read/write head  30  in which the write element  32  leads the read element  34 . In the data region or data sector leading up to the next servo sector or servo wedge or ID (SD) region, the R/W separation gap in the data sector immediately preceding the servo wedge is eliminated because there is no need to terminate the write operation before the read head reaches the servo wedge (front end of the servo wedge). Because the write operation in the data sector terminates as the write element reaches the servo sector, there is extra time due to the R/W separation gap before the read element passes over the servo sector. The R/W separation gap is typically large enough to allow time for disturbance to decay due to switching from write mode to read mode or write to read (W/R) recovery. As a result, the W/R recovery time can be hidden. After going over the servo wedge, the write operation by the write element  32  in the data sector immediately following the servo wedge (back end of the servo wedge) does not start until the read element  34  completes reading in the servo wedge, so that the R/W separation gap of delay in the write operation remains. In this configuration, the additional delay due to W/R recovery is eliminated provided that the it is shorter than or equal to the R/W separation gap. If the W/R recovery is longer than the R/W separation gap, the W/R recovery is not eliminated but is still reduced by an amount equal to the size of the R/W separation gap. This reduces the loss of area for write operation. 
     To further eliminate or reduce delay in the write operation due to the R/W separation gap, the servo wedge information is arranged such that information that is not needed for write operation is placed at a back end region  40  of the servo wedge, as seen in  FIG. 3 . If the size of the back end region  40  is equal to or larger than the R/W separation gap, write operation by the write element  32  can start immediately after going over the back end of the servo wedge so as to eliminate the delay due to the R/W separation gap. If the size of the back end region  40  is smaller than the R/W separation gap, write operation by the write element  32  can start as soon as the read element  34  enters the back end region  40  so as to reduce the delay due to the R/W separation gap by an amount equal to the size of the back end region  40 . 
     Examples of information in the servo wedge not needed for write operation include cylinder ID, read repeatable runout (RRO) field, part of fine tracking signal not necessary for write operation, and the like. As described in U.S. Patent Publication No. 2005/0057837A1, a burst area is information to indicate the relative position of the current location of the head to the track center, while a recording area to write eccentricity correction data in the servo frame is referred to as a post code area. The RRO data is after the PES burst. See also U.S. Pat. No. 6,097,565 at FIG. 5 (57) and FIG. 5A (62). The read RRO is not used during write operation, but only during read operation. The magnetic head can stop the read operation of the read RRO field located after the servo burst early and get ready for the write operation to the data area earlier. 
       FIG. 4  shows an example of rearranging the servo wedge information such that information that is not needed for write operation is placed at a back end region of the servo wedge.  FIG. 4A  shows the original arrangement of the servo wedge information involving a quad burst. In  FIG. 4B , the servo address mark (SAM) is reduced in the number of bits (to 9 bits in the example), and the cylinder address is replaced by a partial cylinder address to further reduce the size of the servo sector. In  FIG. 4C , the partial cylinder address is moved to the back end of the servo sector. In this example, the partial cylinder address and quad bursts C and D are not needed for the write operation. The partial cylinder address is used for read and seek, but not for track following. The quad bursts C and D are part of the fine position tracking signal not necessary for the write operation. Thus, the end of servo for write is located between quad burst B and quad burst C, while the end of servo for read and seek is located at the back end of the servo sector. 
     According to the present technique employing a write element before the read element and arranging the servo information in the servo sector, the loss of area for write operation (extra overhead) in the prior art (R/W separation and W/R recovery) can be reduced or eliminated. In a typical example, the W/R recovery field is about 20% of the servo overhead, and R/W offset is about 40% of the servo overhead. If the servo sectors occupy 10% of the disk surface, this approach of reducing or eliminating the extra overhead can potentially save about 6% of the total area or “real estate” for write operation. Additional saving can be achieved by having better format efficiency due to smaller servo overhead. 
     The gap between the read element and the write element is a fixed geometric quantity, but the offset which is actually required is a function of the applied skew angle, and hence the radial position, of the magnetic head. The skew angle is illustrated in  FIG. 5  for a conventional magnetic head with the read element disposed before the write element. The positions of the read element and the write element are reversed in the present invention. Referring back to  FIG. 3 , the additional delay due to W/R recovery is eliminated provided that the it is shorter than or equal to the R/W separation gap; whereas if the W/R recovery is longer than the R/W separation gap, the W/R recovery is not eliminated but is still reduced by an amount equal to the size of the R/W separation gap. This does not take into account the skew angle of the magnetic head with respect to the tracks on the disk. This does not present an issue if the W/R recovery is sufficiently smaller than the R/W separation gap. Otherwise, the adaptive formatting technique can be used to account for the effect of the skew angle. Similarly, referring back to  FIG. 3  above, if the back end region  40  is equal to or larger than the R/W separation gap, write operation by the write element  32  can start immediately after going over the back end of the servo wedge so as to eliminate the delay due to the R/W separation gap; whereas if the back end region  40  is smaller than the R/W separation gap, write operation by the write element  32  can start as soon as the read element  34  enters the back end region  40  so as to reduce the delay due to the R/W separation gap by an amount equal to the size of the back end region  40 . This does not take into account the skew angle of the magnetic head with respect to the tracks on the disk. This does not present an issue if the back end region  40  is sufficiently larger than the R/W separation gap. Otherwise, the adaptive formatting technique can be used to account for the effect of the skew angle. 
     The adaptive formatting technique is described, for instance, in U.S. Pat. No. 6,781,786 and U.S. Patent Publication No. 2005/017671A1, the entire disclosures of which are incorporated herein by reference. 
     For example, U.S. Patent Publication No. 2005/017671A1 discloses writing a data track having a length that is based on an arc of the rotary actuator, the radial position of the read/write head with respect to the hard disk, and the offset between the read element and the write element.  FIG. 6  depicts a detailed physical arrangement of a rotary actuator  601  of a hard disk drive in relationship to a hard disk  602 . In  FIG. 6 , the rotary actuator  601  includes an actuator end  603  that is integral with a voice coil motor, an actuator arm  604 , and an offset read/write head  605  that is located distal from the actuator end  603 . The hard disk  602  rotates counter-clockwise in  FIG. 6 . As the rotary actuator  601  is driven by the voice coil motor, the rotary actuator  601  pivots around a pivot point  606 . The rotary actuator  601  is depicted in  FIG. 6  with the read/write head  605  in a first position at a radius A from the center of the hard disk  602  and with the read/write head  605  in a second position at a radius A′ from the center of the hard disk  602 . A distance B is the distance between the pivot  606  and the center  607  of the hard disk  602 . A distance C is the distance between the pivot  606  and the read head sensor  605 . 
       FIG. 7  depicts the physical arrangement of the rotary actuator  601  and the hard disk  602 , shown in  FIG. 6 , with the rotary actuator  601  removed. As the rotary actuator  601  pivots around the pivot  606 , the radius A changes while the distances B and C remain constant. The cosine of an angle D is given by: 
     
       
         
           
             
               cos 
               ⁢ 
               
                   
               
               ⁢ 
               D 
             
             = 
             
               
                 
                   
                     A 
                     2 
                   
                   + 
                   
                     C 
                     2 
                   
                   - 
                   
                     B 
                     2 
                   
                 
                 
                   2 
                   ⁢ 
                   A 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   C 
                 
               
               . 
             
           
         
       
     
       FIG. 8  depicts the physical arrangement used for determining an angle E of a read/write head  801  with respect to a circumferential data track  803  at a given radius A. The read/write head  801  includes a read element  801  and a write element  802 . To adapt this technique to the present invention, the positions of the read element and the write element will be reversed. The angle E is given by
   E= 90 °−D.    
     The effective read/write separation gap along the circumferential track decreases at the outer and inner diameters of a hard disk due to effect of the skew angle, as illustrated in  FIG. 9 . A read/write head  900  having a read element  901  and a write element  902  is depicted near the inner diameter  910 , at zero skew  920  (i.e., E=0°) and near the outer diameter  930  of a hard disk with respect to a servo sample (servo sector)  903  and customer data (data sector)  904 . Near the inner diameter  910  and near the outer diameter  930 , the respective separations  911  and  931  between the read element  901  and the write element  902  are reduced in comparison to separation  921  when the read/write head  900  is at zero skew  920 . It is noted that  FIG. 9  shows the read element leading the write element, and that the positions of the read element and the write element will be reversed in the present invention. 
     Due to the skew angles at the inner and outer diameters, the effective read/write separation gaps along the circumferential track are smaller as compared to the write to read recovery. As a result, the adaptive formatting technique can be used to account for the effect of the skew angle to ensure that either the write to read recovery is equal to or smaller than the effective read/write separation gap, or the write operation ends sufficiently early before reading begins in the servo sector to allow time for the write to read recovery. 
     Similarly, owing to the skew angles at the inner and outer diameters, the effective read/write separation gaps along the circumferential track are smaller as compared to the back end portion of the servo sector. If the read/write separation gap at zero skew angle is equal to or smaller than the size of the back end portion, the effective read/write separation gaps at other skew angles would be smaller than the size of the back end portion, so that writing operation can start at the beginning of the next data sector. Even if the read/write separation gap at zero skew angle is larger than the size of the back end portion, the effective read/write separation gaps at other skew angles may become equal to or smaller than the size of the back end portion, so that writing operation can start sooner, for instance, at the inner and outer diameters. Therefore, the adaptive formatting technique can be used to account for the effect of the skew angle so as to start the write operation sooner at the inner and outer diameters as compared to the zero skew angle. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.