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SQ (program)
SQ (''squeeze'') is a computer program, devised by Richard (Dick) Greenlaw circa 1981, which was used in the early 1980s on both DOS and CP/M computer systems to compress files so they use less space. Files compressed by SQ are identified by changing the middle initial of the extension to "Q", so that text files ended with the extension , executable files ended with the extension or , documents with , etc. SQ used static Huffman coding as the compression algorithm. Groups of files were often combined into an archive using the LU program, which created .LBR files containing all the files needed for a particular group, such as all the files needed to install an application. Typically such files were either individually compressed (because LU did not compress files) or the LBR archive was itself compressed with SQ (similarly to the use of tar and gzip together). With the development of the ARC program (which combined both compression and archiving into one program) and its ARC ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CP/M
CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initially confined to single-tasking on 8-bit processors and no more than 64 kilobytes of memory, later versions of CP/M added multi-user variations and were migrated to 16-bit processors. The combination of CP/M and S-100 bus computers became an early standard in the microcomputer industry. This computer platform was widely used in business through the late 1970s and into the mid-1980s. CP/M increased the market size for both hardware and software by greatly reducing the amount of programming required to install an application on a new manufacturer's computer. An important driver of software innovation was the advent of (comparatively) low-cost microcomputers running CP/M, as independent programmers and hackers bought them and shared their crea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Huffman Coding
In computer science and information theory, a Huffman code is a particular type of optimal prefix code that is commonly used for lossless data compression. The process of finding or using such a code proceeds by means of Huffman coding, an algorithm developed by David A. Huffman while he was a Sc.D. student at MIT, and published in the 1952 paper "A Method for the Construction of Minimum-Redundancy Codes". The output from Huffman's algorithm can be viewed as a variable-length code table for encoding a source symbol (such as a character in a file). The algorithm derives this table from the estimated probability or frequency of occurrence (''weight'') for each possible value of the source symbol. As in other entropy encoding methods, more common symbols are generally represented using fewer bits than less common symbols. Huffman's method can be efficiently implemented, finding a code in time linear to the number of input weights if these weights are sorted. However, although opt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LBR (file Format)
The .LBR file format was an archive file format invented by Gary P. Novosielski used on CP/M and DOS operating systems during the early 1980s. Packages in .LBR format were created by the LU program. It can act in interactive and parameter-driven mode, and can add, extract, delete files from the LBR package.LU v210 User Manual from SimTel archiv A companion program, still developed by Novosielski, is LRUN.COM : a small program which allows running a .COM (executable code) directly from any library, without having to extract it to a separate disk file. Later compatible programs like NULU arrived for .LBR creation, and many tools such as LT and QL were capable of extracting from .LBR archives. .LBR is an abbreviation of "Library", and, resembling the .tar In computing, tar is a computer software utility for collecting many files into one archive file, often referred to as a tarball, for distribution or backup purposes. The name is derived from "tape archive", as it was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tar (file Format)
In computing, tar is a computer software utility for collecting many files into one archive file, often referred to as a tarball, for distribution or backup purposes. The name is derived from "tape archive", as it was originally developed to write data to sequential I/O devices with no file system of their own. The archive data sets created by tar contain various file system parameters, such as name, timestamps, ownership, file-access permissions, and directory organization. POSIX abandoned ''tar'' in favor of ''pax'', yet ''tar'' sees continued widespread use. History The command-line utility was first introduced in the Version 7 Unix in January 1979, replacing the tp program (which in turn replaced "tap"). The file structure to store this information was standardized in POSIX.1-1988 and later POSIX.1-2001, and became a format supported by most modern file archiving systems. The tar command was abandoned in POSIX.1-2001 in favor of pax command, which was to support ustar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gzip
gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and intended for use by GNU (from where the "g" of gzip is derived). Version 0.1 was first publicly released on 31 October 1992, and version 1.0 followed in February 1993. The decompression of the ''gzip'' format can be implemented as a streaming algorithm, an important feature for Web protocols, data interchange and ETL (in standard pipes) applications. File format gzip is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algorithms which, at the time, limited the usability of compress and other popular archivers. "gzip" is often also used to refer to the gzip file format, which is: * a 10-byte header, contai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ARC (file Format)
ARC is a lossless data compression and archival format by System Enhancement Associates (SEA). The file format and the program were both called ARC. The format is known as the subject of controversy in the 1980s, part of important debates over what would later be known as open formats. ARC was extremely popular during the early days of the dial-up BBS. ARC was convenient as it combined the functions of the SQ program to compress files and the LU program to create .LBR archives of multiple files. The format was later replaced by the ZIP format, which offered better compression ratios and the ability to retain directory structures through the compression/decompression process. The .arc filename extension is often used for several unrelated file archive-like file types. For example, the Internet Archive used its own ARC format to store multiple web resources into a single file. The FreeArc archiver also uses .arc extension, but uses a completely different file format. Nintendo u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porting
In software engineering, porting is the process of adapting software for the purpose of achieving some form of execution in a computing environment that is different from the one that a given program (meant for such execution) was originally designed for (e.g., different CPU, operating system, or third party library). The term is also used when software/hardware is changed to make them usable in different environments. Software is ''portable'' when the cost of porting it to a new platform is significantly less than the cost of writing it from scratch. The lower the cost of porting software relative to its implementation cost, the more portable it is said to be. Etymology The term "port" is derived from the Latin '' portāre'', meaning "to carry". When code is not compatible with a particular operating system or architecture, the code must be "carried" to the new system. The term is not generally applied to the process of adapting software to run with less memory on the sam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Archive Formats
In computing, an archive file is a computer file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compress files to use less storage space. Archive files often store directory structures, error detection and correction information, arbitrary comments, and sometimes use built-in encryption. Applications Portability Archive files are particularly useful in that they store file system data and metadata within the contents of a particular file, and thus can be stored on systems or sent over channels that do not support the file system in question, only file contents – examples include sending a directory structure over email, files with names unsupported on the target file system due to length or characters, and retaining files' date and time information. Additionally, it facilitates transferring high numbers of small files such as resource ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Compression Software
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. A datum is an individual value in a collection of data. Data is usually organized into structures such as tables that provide additional context and meaning, and which may themselves be used as data in larger structures. Data may be used as variables in a computational process. Data may represent abstract ideas or concrete measurements. Data is commonly used in scientific research, economics, and in virtually every other form of human organizational activity. Examples of data sets include price indices (such as consumer price index), unemployment rates, literacy rates, and census data. In this context, data represents the raw facts and figures which can be used in such a manner in order to capture the useful information out of it. Dat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
