Patent
1996-09-11
1998-05-05
Amsbury, Wayne
395615, 39520077, G06F 1730, G06F 1516
Patent
active
057489556
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to compression of data in computer information systems, and more particularly to a memory structure and also to methods which provide a means of storing information in and retrieving information from that structure.
One of the most common uses of computers is that of storing information. In business, this is typically done by a user entering data into a display screen via a keyboard, which is then stored in computer memory, either volatile or permanent, such as RAM or rotating disk memory. Also, today, data such as images of documents and photographs is commonly entered into computers via a scanner. Many other types of data, such as sounds, video images and the output of scientific instruments may be stored in computers.
Before storing information, a computer, via the appropriate peripheral device, and in some cases with the help of the operating system, first breaks down the information into discrete units of data, which will be called "data units". For example, sound may be broken down into separate audio samples, images into discrete pixels, and keyboard characters are transmitted from the keyboard in the form of a series of discrete codes. The discrete units are then recorded as digital data in computer memory.
In order to retrieve information from a computer, the stored discrete data units are played back, via a suitable device, which re-creates the original type of data (an image, sounds, characters etc.) with the appropriate values in the right order, and in so doing, creates a new instance of the original information.
Perhaps the clearest example is that of character data. In the case of this data type, data from the keyboard is typically stored in computer memory as a digital form of the characters which are typed. Most computer operating systems and database management systems record typed information in a 1:1 ratio. For example, the typed word "hello" is typically stored as five letters. This is, five data units exist outside computer storage and five data units are stored inside.
Some languages such as Chinese require multi-byte character sets. Even though more than one byte of storage may be required to store a single character, these characters are still stored in a 1:1 ratio because each character outside computer memory is separately recorded as a single character inside computer memory.
Recording information in a 1:1 ratio can result in inefficient use of storage space. This is particularly so in respect of large amounts of information which contain contiguously repeated data of the same values; that is, information such as images, sounds and large text documents. For examples: text typically includes repeated blanks: images of documents, significant area of white; and pictures, various areas of the same colour and intensity.
Some computer operating systems use data compression methods to reduce the amount of space required to store information. For example, rather than store 30 typed spaces, such an operating system might store one space and the number 30 along with a flag to indicate that this information is compressed. A variety of compression algorithms are nowadays commonly employed in operating systems to reduce the space required to store contiguous repetitions of the same data values. Such algorithms cannot compress non-contiguous repetitions of data values. Other algorithms may compress non-contiguous data, but rely on pre-existing dictionaries of code words which are generally fixed before the algorithms are used.
Compression algorithms, traditionally part of major operating systems such as VMS and VS, may be a separate product in respect of smaller operating systems, such as earlier releases of MS-DOS, which do not have compression. Whether an integral part of an operating system or added later, compression algorithms perform an operating system role, that is, they are part of the low-level interface between applications and hardware.
Compression algorithms often function in a client-sever relationship with other parts of an op
REFERENCES:
patent: 4491934 (1985-01-01), Heinz
"Algorithm to Identify Common Phrases in Source Text," IBM Technical Disclosure Bullentin, vol. 33, No. 12, May 1991, pp. 150-152.
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