COMPUTER SYSTEMS NETWORK

Computer Systems Network

Computer Systems Network

Introduction

Goal of data compression is to reduce redundancy in stored or communicated data, thereby increasing effective data density. Data compression has important application in areas of file storage and distributed systems. Concepts of information theory, which refers to objectives and evaluation of data compression methods, are discussed briefly. THE framework for evaluating and comparing methods are constructed and applied to algorithms presented. Comparisons of both theoretical and empirical natures are presented and future research possibilities are suggested.

Task I

This section surveys the variety of data compression methods spanning almost forty years of research, work of Shannon, Fano and Huffman in late 40 for the technique developed in 1986.

Data compression is often referred to as encryption, where encryption is the very general term covering any special data representation that satisfies the particular need. Information theory is defined as study of efficient coding and its consequences in form of transmission rate and probability of error. Data compression can be considered the branch of information theory in which main objective is to minimize amount of data to be transmitted. Purpose of this paper is to present and analyze the variety of data compression algorithms.

THE simple characterization of data compression is that it is to transform the string into the representation (e.g., ASCII) into the new string (of bits, for example) that contains same information but whose length is most small as possible. Data compression has important application in areas of data transmission and data storage. Many data processing applications require storage of large volumes of data, and number of applications is increasing as use of computers extends to new disciplines. At same time, proliferation of computer communication networks resulting in massive transfer of data over communication links. compression of data to be stored or transmitted reduces storage and / or communication costs. When amount of data transmitted is reduced, effect is to increase capacity of communication channel. Similarly, compression of the file to half its original size is equivalent to doubling capacity of storage media. You can then become feasible to store data at the higher level, therefore faster, storage hierarchy and reduce load on input / output channel computer system.

Many of methods discussed in this paper are applied in production systems. UNIX utilities compact and compress based on methods to be discussed. Popular file systems such as ARC and PKARC files used techniques. Savings achieved by data compression can be dramatic; reducing to 80% is not uncommon. Typical values provides compact compression are: Text (38%) Pascal source (43%), C source (36%) and binary (19%). Compresses usually achieves the better compression (50-60% in text and source code and English), and takes less time to calculate. Arithmetic coding has been reported to reduce the file to anywhere from 12.1 to 73.5% of original size [Witten et al. 1987]. Cormack program reports data compression based on Huffman coding reduced size of the large database of students record of 42.1% when only part of information is ...