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Control Method for Random Access Storage Device with an Embedded Compression Function

IP.com Disclosure Number: IPCOM000115695D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 78K

Publishing Venue

IBM

Related People

Niijima, H: AUTHOR [+2]

Abstract

Disclosed is a control method for a random access storage device with an embedded compression function. The compression unit of the Lempel-Ziv algorithm usually needs 2KB-8KB to get a high compression ratio, while the size of a sector in a disk drive only is 512 Bytes. This method allows sector read/write operations that have large internal compression unit.

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Control Method for Random Access Storage Device with an Embedded
Compression Function

      Disclosed is a control method for a random access storage
device with an embedded compression function.  The compression unit
of the Lempel-Ziv algorithm usually needs 2KB-8KB to get a high
compression ratio, while the size of a sector in a disk drive only is
512 Bytes.  This method allows sector read/write operations that have
large internal compression unit.

      Figs. 1 and 2 illustrate concepts of two different methods with
examples.  In these examples, a compressed unit, called a cluster
consists of 16 sectors.  A cluster in method 1 is a set of
consecutive 16 logical sectors, and in method 2, it is any
combination of 16 sectors written in order on the disk drive.  The
method provides a logical-cluster-to-physical-cluster allocation map.
In method 1, the allocation map points to the location of each
cluster, but in method 2, it also points to the location of each
sector.  The read operations in both methods are the same.  The
compressed cluster that includes the requested sector is selected by
the allocation map and decompressed into a read buffer, and the
sector is then output.  If the next requested sector is found in the
buffer, no decompress operation is necessary; thus, the buffer works
as a disk cache.  In the sector write operation of method 1, the
cluster that includes the write target sector is decompressed into
the write buffer and the sector is repl...