Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2000-01-20
2003-04-22
Yoo, Do Hyun (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S112000, C710S052000
Reexamination Certificate
active
06553454
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a storage device used as an external storage device for a computer or the like. More particularly, this invention relates to a storage device which can shorten a time required for a rearrangement process of commands and can shorten a time required for access to a magnetic disk.
BACKGROUND OF THE INVENTION
As an external storage device for a computer or the like, a storage device using a large-capacity magnetic disk as a recording medium is popularly used. The density of storage devices of this type is increasing year by year with the improvement in the characteristic of the magnetic disks, the magnetic heads, and the like. With such an increase in the density, it is required that access time and processing is shortened. An effective solution for this is aspired after.
FIG. 9
is a block diagram showing the configuration of a conventional storage device
10
. As shown in
FIG. 9
, the storage device
10
is connected to a host
30
such as a computer through SCSI (small computer system interface). The storage device
10
performs a write operation, a read operation, and the like on the basis of a command (for example, write command or read command) from the host
30
. The write operation here means an operation for writing data on a magnetic disk
17
(to be described later), and the write command is a command for executing this write operation. On the other hand the read operation means an operation for reading data from the magnetic disk
17
, and the read command is a command for executing the read operation.
The command is described in a form widely known as CDB (command descriptor block), and includes a command code representing the type of the command and information such as an address on the magnetic disk
17
in execution of the command. A control section
11
performs analysis of a command received from the host
30
through an I/F section
12
, transmission of a status to the host
30
, queuing of the commands, rearrangement of commands, and the like. Queuing of the commands is an operation of adding commands sequentially issued from the host
30
to a command queue Q
1
shown in FIG.
10
. The command queue Q
1
is stored in a buffer memory
13
, and the commands are sequentially executed from the start command of the command queue Q
1
.
In an example shown in
FIG. 10
, the command queue Q
1
consists of four commands, that is, Commands C
1
to C
4
. The rearrangement of commands is a process of selecting a command to be executed next to a command under execution from the command queue Q
1
and moving the selected command to the header of the command queue Q
1
. In this case, the command to be selected is a command with the shortest seek time explained later.
Returning back to
FIG. 9
, the buffer memory
13
temporarily stores the command queue Q
1
, data read from the magnetic disk
17
, and data to be written on the magnetic disk
17
. A command execution section
14
sequentially executes the command from the start in command queue Q
1
command to perform control for reading data from the magnetic disk
17
or writing data on the magnetic disk
17
. A read/write section
15
comprises a modulation circuit (not shown) for modulating data to be written on the magnetic disk
17
, a parallel/serial conversion circuit for converting parallel data into serial data, a demodulation circuit (not shown) for demodulating data read from the magnetic disk
17
, and the like.
A head
16
is arranged to be close to the magnetic disk
17
, which writes data on and reads data from the magnetic disk
17
. More specifically, the head
16
writes data on the magnetic disk
17
using a magnetic field generated by a recording current supplied to a coil (not shown) in the write operation, and magnetically detects, as a reproduced voltage, the data recorded on the magnetic disk
17
. The head
16
is moved along the recording surface of the magnetic disk
17
by a voice coil motor (“VCM”)
18
.
The magnetic disk
17
is a disk-like recording medium on which data is magnetically recorded, and is rotationally driven at a high speed by an spindle motor (“SPM”)
19
. A servo section
20
controls drive currents supplied to the VCM
18
and the SPM
19
to perform positioning control of the head
16
with respect to the magnetic disk
17
.
An operation of the conventional storage device
10
will be explained below with reference to
FIGS. 10
,
11
, and
12
. The rearrangement process of commands will be explained first. When commands are sequentially transmitted from the host
30
shown in
FIG. 9
, these commands are sequentially input to the control section
11
through the I/F section
12
. The control section
11
then analyses the commands and queues the commands into a command queue in the buffer memory
13
in the input order. The command execution section
14
executes the start command of the command queue.
In this case, a command C
0
shown in
FIG. 12
is executed by the command execution section
14
, and the command queue Q
1
shown in
FIG. 10
is stored in the buffer memory
13
. More specifically, as shown in
FIG. 12
, it is assumed that the head
16
is on a track TR
1
of the magnetic disk
17
and that data is read from a sector of, for example, the track TR
1
depending on the command C
0
. The command queue Q
1
shown in
FIG. 10
consists of the command C
1
to C
4
.
As described above, in execution of the command C
0
, the control section
11
shown in
FIG. 9
executes the rearrangement process of commands according to the flowchart shown in FIG.
11
. More specifically, in step SA
1
shown in
FIG. 11
, the control section
11
initializes the command C, at the start of the command queue Q
1
(see
FIG. 10
) as an optimum solution command and initializes the next command C
2
as a compared command. The control section
11
then proceeds to step SA
2
. In this case, the optimum solution command is a command executed next to the command C
0
under execution. The optimum solution command is a command in which a seek time of the head
16
after the execution of the command C
0
is the shortest in the command queue Q
1
.
The command to be initialized as the optimum solution command is a command which can be rearranged in the command queue Q
1
, for example, read command, or write command. When the start command of the command queue Q
1
is a command which cannot be rearranged, a command which is queued below the start command and closest to the start command is initialized as the optimum solution command.
In step SA
2
, the control section
11
determines whether or not a compared command (=command C
2
) is a command that can be rearranged (a read command, a write command, or the like) If the result of determination in step SA
2
is “Yes”, then the control section
11
proceeds to step SA
3
. If the result of determination in step SA
2
is “No”, then the control section
11
proceeds to step SA
7
.
In step SA
3
, the control section
11
calculates the physical address of an optimum solution command (=command C
1
) and the physical address of a compared command (=command C
2
), and then proceeds to step SA
4
. The physical address of the optimum solution command is a position of the head
16
on the magnetic disk
17
shown in
FIG. 12
when execution of the optimum solution command is started. Similarly, the compared command is a position of the head
16
on the magnetic disk
17
when execution of the compared command is started.
The control section
11
calculates a first seek time T
1
of the optimum solution command and a second seek time T
2
of the compared command in step SA
4
, and then proceeds to step SA
5
. The first seek time T
1
is a time from when execution of a command under execution (in this case, the command C
0
) is finished to the time when execution of the optimum solution command (in this case, the command C
1
) is started. In other words, the first seek time T
1
is a time required for movement of the head
16
from a point a at which the head
16
is located when th
Fujitsu Limited
Greer Burns & Crain Ltd.
Moazzami Nasser
Yoo Do Hyun
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