GB2339056A

GB2339056A - Optimizing skew in a hard disk drive

Info

Publication number: GB2339056A
Application number: GB9922730A
Authority: GB
Inventors: Byung-Joon Lee; Jae-Sung Lee
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1995-08-25
Filing date: 1996-08-23
Publication date: 2000-01-12
Anticipated expiration: 2016-08-23
Also published as: GB2339056B; GB2339057A; GB9922730D0; GB2339057B; GB9922734D0

Description

2339056 METHOD FOR OPTIMIZING SKEW OF HARD DISK DRIVE The present

invention relates to a hard disk drive, and, more particularly, to a method for optimizing skew of the hard disk drive in which a skew value suitable for each drive is set so as to improve performance of the drive.

A hard disk drive functions to reproduce data re.corded on a disk using a magnetic head or to record new data thereon.

As the capacity, density and miniaturization of hard disks increase, the BPI (bits per inch) and TPI (tracks per inch) are both increased. Accordingly, a more precise and rapid head position control method and a more accurate mechanical mechanism are required.

FIG. I shows the structure of a disk adopted in a general hard disk drive. Referring to FIG. 1, a disk 11 is comprised of a plurality of sectors 12 which are units for storing and reading data, a track 13 which is a circular path made by the sectors 12, and a cylinder 14 which is a cylindric form made of the tracks 13.

When a read/write command is issued by the microprocessor of a host computer, a hard disk drive having the disk 11 installed therein converts logical addresses of the cylinder, head and sector according to the read/write command into physical addresses of the cylinder, head and sector in the drive and read/writes the sectors of the required numbers by moving the head to a corresponding position on the disk.

I Assembly errors may occur, however, due to the tolerance for each part in manufacturing a hard disk drive. Thus, it is difficult for the hard disk drive to maintain the same product features. This fact is further intensified as the trend for high-density and miniaturization proceeds. For instance, as shown in FIGS. 2A and 2B, the arrangement of heads HD1 and HD2, i.e., a degree of change in the arrangement of the heads HD1 and HD2 aligned in a row on a co-axial cylinder, affects reliability or function of the whole drive. When such change happens, the setting time for stable head positioning of a target head is prolonged since a phase error signal (PES) increases after head switching.

Generally, in the.head switching action of the hard disk drive, the head is switched according to servo information while the head is positioned on a disk surface, and it is then determined whether the position difference of the head is stable. Reading and writing is performed after verification of a corresponding sector ID. At this time, the head position is changed to the first sector portion from a physical index position to perform reading and writing shortly after the stable head setting: this is referred to as track skew. The time from head switching to reading and writing from or to a corresponding sector is referred to as track skew time. For instance, assuming that there are two heads in the hard disk drive, the time from reading and writing with respect to the last sector (Sn) of a head 0 (HDO) as in FIG. 3 to continuous reading and writing with respect to the first sector (Si) of a head 1 (HD1) is referred to as track skew time t4 which 2 includes head switching time ti, head settling time t2 and controller ready time t3 for reading and writing.

Also, in FIG. 4, the switching of reading and writing from the last sector (Sn) and the last head (HDN) of the N-th track to the first sector (SI) and the first head (HDO) of the (N+I)th track is referred to as cylinder skew, and the necessary time for the above switching is cylinder skew time t9. At this stage, like the track skew time t4, the cylinder skew time t9 includes head switching time t5, head settling time t6 and controller ready time t7 for reading and writing as well as 1- track seek time t8.

The above skew parameters have values which differ from each other in accordance with a zone structured for constant density recording (CDR). However, for a conventional hard disk drive, an equal skew value is applied to all the drives by generally calculating the head switching time, the head settling time, the controller ready time and the 1-track seek time without considering the characteristic of each hard disk drive. That is, though the skew value can be changed without limit in accordance with elements determining the characteristic of each hard disk drive such as a head, a spindle motor, a voice coil motor, a servo, a circuit device, etc., not the optimal value for each drive, but a uniform value having a predetermined tolerance, is set as the skew value. Thus, the setting time of the head is prolonged when the arrangement of the head has changed due to the deformation of a drive, and the skew time becomes longer. That is, since the first sector position is determined by the calculated skew 3 time, direct reading and writing of the first sector is not available, but only after one rotation of a disk, reading and writing is made possible. Accordingly, a time delay occurs which is equal to one rotation of the disk, resulting in lower performance. Consequently, considering an individual drive, the performance of each drive is reduced due to the equally setting of the skew value. Further, it is burdensome to repeat a complicated process of checking the drive characteristic and again setting the optimal skew value suitable for it in the design change of the drive.

To solve the above problems, it is an object of the present invention to provide a skew optimizing method in a hard disk drive by which an optimal skew value for each drive can be provided without setting the drive skew value to an equal size.

To achieve the above object, there is provided a skew optimizing method for a hard disk drive comprising the steps of:

(a) initializing a zone number and head number by formatting without the track skew of the hard disk drive; (b) searching for a sector ID while switching heads at the current zone and head; (c) calculating the distance between two sector ID's during the head switching; (d) calculating and storing track skew based on the data searched for in said step (b), and increasing the head number; (e) determining whether the track skew of the final head is still to be calculated; 4 (f) if it is determined that the track skew of the final head was not calculated in said step (e), returning the program to said step (b); (g) if it is determined that the track skew of the final head was calculated in said step (e), sequentially searching for a sector ID from a particular track N of the current zone to the next track N+1; (h) calculating the distance between two sector ID's during the sequential searching in said step (g); - (i) calculating and storing a cylinder skew based on the data searched for in said step (g); (j) increasing the zone number based on the calculated cylinder skew value and determining whether the cylinder skew of the final zone has been calculated; (k) if it is determined that the cylinder skew of the last zone was not calculated in said step (j), initializing the head number and returning the program to said step (b) and (1) if it is determined that the cylinder skew of the last zone was calculated in said step (j), storing the skew value for each track and zone in a cylinder used for information storage and formatting with the track skew.

Specific embodiments of the present invention are described in detail below, by way of example, with reference to the attached drawings, in which:

FIG. 1 is a perspective view illustrating the structure of a disk adopted in a general hard disk drive; FIGS. 2A and 2B are schematic views illustrating the characteristic of the head arrangement adopted in the general hard disk drive; FIG. 3 is a timing diagram for explaining track skew in the general hard disk drive; FIG. 4 is a timing diagram for explaining cylinder skew in the general hard disk drive; FIG. 5 is a block diagram illustrating the system configuration of a hard disk drive where an embodiment of the method of the present invention is adopted; FIG. 6 is a flow chart for explaining a skew optimizing method for a hard disk drive; FIGS. 7A and 7B are flow charts for explaining a skew optimizing method for a hard disk drive according to the present invention; and FIG. 8 is a flow chart for explaining another skew optimizing method.

The system configuration of a hard disk drive to which an embodiment of the method of the present invention is adopted will be described, referring to FIG. 5.

In FIG. 5, in the hard disk drive, there are provided a pair of magnetic disks 500, and four magnetic heads 501 are provided, corresponding to the upper and lower surfaces of each magnetic disk 500. The magnetic heads 501 are each installed at the end portion of one of the arm members 502 associated with an E-block assembly 503.

A preamplifier 504 amplifies a predetermined signal read out from the disk 500 using the magnetic head 501 and transmits the amplified signal to a reading and writing 6 channel circuit 505. In the meantime, the preamplifier 504 applies encoded writing data transmitted from the reading and writing channel circuit 505 to a predetermined head among the magnetic heads 501 to be recorded on the disk 500. At this time, 'the preamplifier 504 selects one of the magnetic heads 501 according to a control signal of a disk data controller DDC 508 which is controlled by a microcontroller 509.

The reading and writing channel circuit 505 detects and decodes data pulses from an input signal to generate read-out data RDATA, and decodes writing data WDATA transmitted from the DDC 508 to transmit the decoded WDATA to the preamplifier 504. The reading and writing channel circuit 505 generates a phase error signal (PES) by decoding head position information, i.e., a part of the servo information, which is recorded on the disk. The PES is transmitted to the microcontroller 509 via an analogto -digital converter (ADC) 506. At this stage, the ADC 506 converts the PES into a digital step value corresponding to a predetermined level and transmits the converted PES.

A track information detector 507 detects from the RDATA, a track number for the current position of the magnetic head 501 and provides the detected data to the microcontroller 509.

The DDC 508 controlled by the microcontroller 509 records the data received from the host computer via the reading and writing channel circuit 505 and the preamplifier 504 or transmits the data read out from the disk 500 to the host computer.

The microcontroller 509 controls the DDC 508 according to 7 a predetermined command received from the host computer to search a track and position the head. In doing so, the microcontroller 509 uses the track number and the PES input from the track information detector 507 and the ADC 506, respectively.

A digital -to-analog converter (DAC) 510 converts the digital signal output from the microcontroller 509 into an analog signal for controlling the position of the magnetic heads 501. A servo driving unit 511 generates driving current for driving an actuator 512 according to the analog signal input from the DAC 510. The actuator 512 drives the magnetic heads 501 to move on the disk in a direction and corresponding to the level of the driving current input from the servo driving unit 511.

The motor controller 513 controls a spindle motor driving unit 514 according to a predetermined disk rotation control command which is output from the microcontroller 509. The spindle motor driving unit 514 drives a spindle motor 515 in accordance with the control of the motor controller 513 thereby to rotate the disk 500.

The skew optimizing method for a hard disk drive according to an embodiment of the present invention will now be described referring to FIGS. 6, 7 and 8.

Referring to FIG. 6, a predetermined measurement position on the disk, such as a zone number or a head number, is initialized to obtain a skew value in step 601. A skew table is then initialized in step 602. The head is moved to the corresponding measurement position in step 603, and the 8 optimal values of the track skew and the cylinder skew are obtained in step 604. In step 605, it is determined whether the position of the head is at the final measurement position or not. If it is determined in step 605, that the current head position is not the final measurement position, the next measurement position is selected, and the process of obtaining the optimal skew value is repeated until the final measurement position is checked, in step 606. If it is determined in step 605 that the current head position is the final measurement position, the optimal skew value obtained is stored in a predetermined area of the drive or a memory device in step 607. The skew optimizing process is then completed.

Referring to FIGS. 7A and 7B, the microcontroller 509 formats a track without track skew using an index as a standard in step 701, so that a zone number and a head number are initialized to zero, respectively, in step 702. A sector ID is then searched for while the head is switched at the current zone and head in step 703. That is, the head number is assigned such that the index search action is performed to include the last sector of the zone positioned at head number 0 and the first sector positioned at head number 1 starting from the track skew position of the first zone (an arbitrary position in the first, the middle and the last positions of the zone). A sector number for the first index search of the head number 1 is then obtained. In step 7Q4, the distance. between two sector ID's is calculated during the head switching. This action is repeated until reliable data can be obtained and stored in the memory device and a predetermined area of the drive. Next, the minimum, mean and maximum values 9 of the stored data are obtained and the last track skew value is calculated and stored by adding a value, related to temperature and moisture, to the minimum, mean and maximum values in step 705. Such a process increases the head number from 0 to 3 (HN=HN+I) in the case of a drive having f our heads in step 706.

In step 707, it is determined whether the track skew with respect to the final head is calculated. When it is determined that the track skew of the final head was not calculated in step 707, the program returns to step 703 so that the track skew value for all the heads can be obtained. When it is determined that the track skew of the final head has been calculated, the sector ID is sequentially sought from a particular track N of the current zone to the next track N+1 is in step 708. The distance between two sector ID's in the sequential seek is calculated, in step 709 and the cylinder skew is calculated and stored in step 710. At this time, the number of the zone increases by one (ZN=ZN+1), in step 711. When it is determined that the cylinder skew with respect to the final zone has not been calculated in step 712, the head number is initialized in step 715, and the program returns to step 703 to obtain the track skew and the cylinder skew values for each zone. When it is determined that the cylinder skew of the final zone has been calculated in step 712, the skew values for each zone and track are stored in a cylinder used for information storage in step 713, and the format is performed with the track skew in step 714. Thus, the skew optimizing process is completed.

FIG. 8 is a flow chart for explaining a self-test process, for example in a burn-in process during the manufacturing of a hard disk drive. Referring to FIG. 8, it is determined in step 8a by the DDC 508 in the hard disk drive whether all the zones and heads of the drive have been subject to a test. If the test for all the zones and heads of the drive is found not to be completed in step 801, the initial skew value in the corresponding zone and head are set in step 802. At this time, the initial skew value is of the order of a few of milliseconds or microseconds, and is set to the largest value of a predetermined range for the test. That is, to obtain the optimal skew value, various skew values for each zone and head are used in the test. Accordingly, the initial skew value for the test is set to the largest value. When the initial skew value is set in the above way, a format is performed in the corresponding zone and head according to the set skew value in step 803. That is, the DDC 508 selects a particular track from the zone and positions a head on the disk to be subjected to the test in accordance with the set initial skew value, and records the sector number on a part of the disk at a position corresponding to the set initial skew value from the start position of the sector. When the format is completed, a required time for reading and writing is measured by performing a reading and writing test while in the above state in step 804. In step 805, it is determined whether the measured value is less than the value set to the initial skew value. When the measured value is not less than the set value, the program goes to step 807, which is for determining whether the test with respect to all the skews to be tested in the corresponding zone and head, has been 11 completed. When the measured value is less than the set value, the current skew value is recorded on a predetermined part of the disk as the optimal skew value of the corresponding zone and head in step 806. In step 807, it is determined whether the test for all the skews of the corresponding zone and head is finished. If the test for all the skews is found not to be finished in step 807, the program returns to step 803 after the current skew value being tested is changed to the next skew value in step 808. When the test for all the skews is completed, the program returns to step 801 after the zone and head are set to the position of the next test, in step 809. When the test of all the zones and heads of the drive is completed by repeating the process from step 801 to step 809, the.skew value requiring the minimum necessary time in each of the zones and heads is set as the optimal skew value and stored in an appropriate area of the disk, in step 810. Accordingly, the head skew optimizing process is finally completed.

As described above, in the skew optimizing method for a hard disk drive according to embodiments of the present invention, the skew value of the drive is not set uniformly, in contrast to the conventional technology: it is set instead with the optimal skew value for each drive. Time for reading and writing information from and to the disk can be sharply reduced so that the performance of the drive can be markedly improved.

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Claims

CLAIMS:

1. A skew optimizing method for a hard disk drive comprising the steps of:

(a) initializing a zone number and head number by formatting without the track skew of the hard disk drive; (b) searching for a sector ID while switching heads at the current zone and head; (c) calculating the distance between two sector ID's during the head switching; (d) calculating and storing track skew based on the data searched for in said step (b), and increasing the head number; (e) determining whether the track skew of the final head is still to be calculated; (f) if it is determined that the track skew of the final head was not calculated in said step (e), returning the program to said step (b); (g) if it is determined that the track skew of the final head was calculated in said step (e), sequentially searching for a sector ID from a particular track N of the current zone to the next track N+1; (h) calculating the distance between two sector ID's during the sequential searching in said step (g); (i) calculating and storing a cylinder skew based on the data searched for in said step (g); (j) increasing the zone number based on the calculated cylinder skew value and determining whether the cylinder skew of the final zone has been calculated; (k) if it is determined that the cylinder skew of the last zone was not calculated in said step (j), initializing 13 the head number and returning the program to said step (b); and (1) if it is determined that the cylinder skew of the last zone was calculated in said step (j), storing the skew value for each track and zone in a cylinder used for information storage and formatting with the track skew.

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