Dynamic magnetic information storage or retrieval – Head – Core
Patent
1996-02-13
1998-09-08
Lee, Thomas C.
Dynamic magnetic information storage or retrieval
Head
Core
395427, 395438, 360 48, G06F 300
Patent
active
058059326
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for and a method of transmitting data, compressed by a loss-less data compression process, between memories, communication devices (including computer terminals), processors, or a host computer and an external memory.
The present invention further relates to an apparatus for and a method of recording data, transferred from an external source and compressed by a loss-less data compression process, on a recording medium, and more particularly to an apparatus for and a method of recording data in an external memory that can be connected to a host computer through an interface bus, e.g., a magnetic disk device such as a hard disk drive, a flexible disk drive, or the like for recording data on and reproducing data from a magnetic disk, or an optical disk drive for recording data on and reproducing data from a recordable optical disk such as a magnetooptical disk, a phase-change disk, or the like.
BACKGROUND ART
Generally, computers have a CPU (central processing unit) for reading program instructions stored in a main memory through a memory control unit and executing the program instructions to process various data and control various devices.
Program instructions are steps of a program (algorithms) for processing data or the like, and a program is normally composed of program instructions as a number of steps.
Some computers effect only simple processing according to a registered small-scale program which is composed of a relatively small number of program instructions. In such computers, a program is already registered in a ROM in the computer. However, a modern computer which carries out a number of data processing operations and control operations is required to have a separate memory means for storing a number of programs and data having a large data length.
It has been customary to employ an auxiliary memory device such as a hard disk drive, an optical disk drive employing a recordable optical disk such as a magnetooptical disk, or a bulk-type semiconductor memory, and connect such an auxiliary memory device to a computer through an interface bus for storing programs and data of large capacity in the auxiliary memory device. According to selective startup or a reading request from an OS (operating system) or an application program, a program or data stored in the auxiliary memory device is read into a main memory device for effecting data processing and controlling operations.
Present trends toward larger-capacity external memory devices have resulted in various techniques proposed to increase the recording capacity of magnetic disks and optical disks.
With the advent of multimedia information processing in recent years, the amount of information required by software applications, e.g., the capacity of programs and the capacity of data handled by programs, has increased at a rate greater than the rate at which the storage capacity of the external memory device increases. Therefore, the data compression technology tends to be more and more important.
One of the data compression techniques which is of the loss-less type (entropy coding or loss-less cording) that causes no data loss is drawing attention because it can increase an apparent capacity when data is recorded in an external memory device and also can effectively use communication lines when data is transmitted.
According to a data compression process based on the loss-less data compression technique, data is compressed by reducing redundant data contained in the data. When the compressed data is expanded, the uncompressed data prior to compression is fully restored without any loss of information.
However, the loss-less data compression technique is of such a nature that a compression ratio at which to compress data, i.e., the ratio of the data length of uncompressed data to the data length of compressed data, remains unknown until all the data is compressed because the compression data varies depending on the content of the data to be compressed.
According to the loss-less data comp
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patent: 4937681 (1990-06-01), Fujinawa et al.
patent: 5467087 (1995-11-01), Chu
patent: 5561824 (1996-10-01), Carreiro et al.
Inokuchi Tatsuya
Kawashima Tetsuji
Chen Anderson I.
Frommer William S.
Lee Thomas C.
Sony Corporation
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