Disk drive device and access sequence therefor

Details Disk drive device and access sequence therefor Disk drive device and access sequence therefor

2000-09-13

2004-02-10

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

Reexamination Certificate

active

06690538

ABSTRACT:

This invention concerns the control of the head position of a disk drive device. More precisely, it concerns the conversion of the logical address (which is contained in an access command that has been issued by an upper level device) to the physical address on the disk.
BACKGROUND OF THE INVENTION
As the capability of processors and the popularity of multimedia have both increased, there has been a greater demand for faster processing speeds and for larger capacities for disk drive devices (which are the external storage devices for computers). In order to increase the storage capacity of disk drives, a plurality of disks are normally provided in each drive. Each disk drive also includes a plurality of heads for recording or regenerating signals, where one head is provided for each disk recording surface.
In order to identify the position on a disk where data will be recorded, the disk is assigned physical addresses that indicate physical locations on the disk. The locations where data are stored upon the disk are identified by: (1) a sector address that identifies the circumferential location on a track; (2) a cylinder address that identifies the radial location on a disk; and (3) a head address that identifies which recording surface on which of the many disks will be used. In response to a disk access request from an upper level device, a logical address, which is controlled by the upper level device, must be correlated to the physical address on the disk. The disk drive device includes memory reserved for a conversion table that converts the logical addresses into the physical addresses.
FIG. 1
shows a cross-section of a disk. In a disk drive device that has a plurality of disks (x number of disks), the physical addresses may be assigned as indicated in FIG.
1
. That is, disks
1
-
1
to
1
-x are stacked on the same axis. The head addresses are assigned in sequence starting from the very top disk, from 0, 1, 2, 3, 4, . . . to 2x−2, 2x−1, as shown in FIG.
1
. The cylinder addresses are assigned in sequence beginning from the outer periphery of a disk (from 0, 1, 2, . . . to y−1). In addition, although not illustrated, sector addresses are assigned in the circumferential direction for each track on all recording surfaces. When recording data, if the data is too large to sequentially fit on a single track, another head or another cylinder track is assigned to accept the remainder of the data.
FIG. 2
shows the access sequence for a disk disclosed in the public release of Japanese Laid-Open Patent Number Hei 1-62886. In this example, there are four disks, which means that there are eight recording surfaces (two per disk).
As shown in
FIG. 2
, within each cylinder, the top surfaces and the bottom surfaces of each disk are alternately accessed in ascending order according to the head address. Thus, for cylinder
0
, the heads are accessed in the following order 0, 1, 2, . . . 6, 7. After the final head (head
7
) is reached, the top surface (head
0
) of the adjacent cylinder will be accessed. As a result, if one sequential string of data does not fit on a single track, the head changes to the next head in the same cylinder, which performs the accessing upon the recording surface that is immediately below the previous recording surface. If the entire string of data cannot fit within that cylinder, the head and the cylinder will change, and accessing begins with the top surface of the adjacent cylinder.
FIG. 3
shows the accessing sequence based on the accessing method disclosed in the public release of Japanese Laid-Open Patent Number Hei 9-63199. In this example there are also four disks, which means that there are eight recording surfaces.
In the example shown in
FIG. 3
, the accessing sequence is substantially the same as that shown in
FIG. 2
(whereby in each cylinder, the top surface and then the bottom surface of each disk are accessed alternately, and after the final head is reached, the adjacent cylinder is accessed). However, in the
FIG. 3
example, when the cylinder changes, the head does not change as it does in the
FIG. 2
example. Instead, in the
FIG. 3
example, the adjacent cylinder on the same recording surface is accessed after the final head on a given cylinder has been accessed. The result is that in even-numbered cylinders, the heads are accessed in ascending order (
0
,
1
,
2
, etc.), while in odd-numbered cylinders, the head are accessed in descending order (
7
,
6
,
5
, etc.).
FIG. 4
shows the accessing sequence for the disk disclosed in the public release of Japanese Laid-Open Patent Number Hei 9-63202. In this case as well, there are four disks, which means that there are eight recording surfaces.
In the
FIG. 4
example, the recording regions are accessed sequentially by cylinder address. Thus, head
0
accesses cylinders
0
,
1
,
2
, etc. in ascending order until finally reaching the final cylinder (cylinder y). At that point, the head changes to head
1
, and the recording surface immediately below is accessed, while remaining in cylinder y. Next, the cylinders are accessed by head
1
in descending order, until reaching cylinder
0
, at which point the head changes to head
2
, where the sequence continues as indicated in the figure. Thus, in general, in the
FIG. 4
example, if sequential data does not entirely fit onto one track, the cylinder changes and the adjacent cylinder on the same recording surface is accessed. Further, if the data does not fit within that recording surface, the head changes and the track of the recording surface immediately below, but still within that same cylinder, is accessed.
The Problems that the Present Invention Attempts to Solve
In order to reduce the rotation wait time that accompanies the head movements when a cylinder changes, the sector numbers between tracks are offset and assigned. These offset sector numbers are referred to as the cylinder skew. In addition, in order to also reduce the rotation wait time that accompanies an access that covers different recording surfaces, the sector numbers between tracks are also offset and assigned. These offset sector numbers are referred to as the head skew.
When the access sequence shown in
FIG. 2
is utilized, the head changes when moving within a single cylinder, as well as when changing from one cylinder to the adjacent cylinder. The amount of movement that accompanies a head change when changing from one cylinder to an adjacent cylinder can be determined by adding together the track pitch and the relative off-track amount between the head at the very top and the head at the very bottom. The relative off-track amount between different heads will depend on things such as the particular specifications of the disk drive device, the direction in which the disk drive device is installed, the temperature of the environment, and the core offset between the write head and the read head. With the narrow track disks that are recently being used, the relative off-track amount sometimes exceeds the track pitch. For this reason, when using the access sequence shown in
FIG. 2
, the cylinder skew is established by considering the worst case value of the relative off-track amount for the track pitch plus head
0
and the final head (head
7
). As a consequence, if there is a large amount of variation in the relative off-track amounts, the amount of head movement that accompanies a cylinder change will be very large. In addition, a large cylinder skew must be established, which becomes a hindrance to increasing the transfer rate of the disk drive device.
In systems using the access sequence shown in
FIG. 3
, no head change accompanies a cylinder change because the cylinder change takes place without a change in the recording surface. As a result, the amount of head movement when the cylinder changes is fixed, when the servo data is recorded, to be within the range of the track pitch accuracy, and this is shorter than the access sequence shown in FIG.
2
. However, since the head changes for each track change within the cylinder in
FIG. 3
(as i

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