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Memory Paging
In computer operating systems, memory paging is a memory management scheme that allows the physical memory used by a program to be non-contiguous. This also helps avoid the problem of memory fragmentation and requiring compaction to reduce fragmentation. Paging is often combined with the related technique of allocating and freeing ''page frames'' and storing pages on and retrieving them from secondary storage in order to allow the aggregate size of the address spaces to exceed the physical memory of the system. For historical reasons, this technique is sometimes referred to as ''swapping''. When combined with virtual memory, it is known as ''paged virtual memory''. In this scheme, the operating system retrieves data from secondary storage in blocks of the same size (pages). Paging is an important part of virtual memory implementations in modern operating systems, using secondary storage to let programs exceed the size of available physical memory. Hardware support is nec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer
A computer is a machine that can be Computer programming, programmed to automatically Execution (computing), carry out sequences of arithmetic or logical operations (''computation''). Modern digital electronic computers can perform generic sets of operations known as Computer program, ''programs'', which enable computers to perform a wide range of tasks. The term computer system may refer to a nominally complete computer that includes the Computer hardware, hardware, operating system, software, and peripheral equipment needed and used for full operation; or to a group of computers that are linked and function together, such as a computer network or computer cluster. A broad range of Programmable logic controller, industrial and Consumer electronics, consumer products use computers as control systems, including simple special-purpose devices like microwave ovens and remote controls, and factory devices like industrial robots. Computers are at the core of general-purpose devices ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instruction Set Architecture
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ''implementation'' of that ISA. In general, an ISA defines the supported instructions, data types, registers, the hardware support for managing main memory, fundamental features (such as the memory consistency, addressing modes, virtual memory), and the input/output model of implementations of the ISA. An ISA specifies the behavior of machine code running on implementations of that ISA in a fashion that does not depend on the characteristics of that implementation, providing binary compatibility between implementations. This enables multiple implementations of an ISA that differ in characteristics such as performance, physical size, and monetary cost (among other things), but t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Berkeley Timesharing System
The Berkeley Timesharing System was a pioneering time-sharing operating system implemented between 1964 and 1967 at the University of California, Berkeley. It was designed as part of Project Genie and marketed by Scientific Data Systems for the SDS 940 computer system. It was the first commercial time-sharing which allowed general-purpose user programming, including machine language. History In the mid-1960s, most computers used batch processing: one user at a time with no interactivity. A few pioneering systems such as the Atlas Supervisor at the University of Manchester, Compatible Time-Sharing System at MIT, and the Dartmouth Time-Sharing System at Dartmouth College required large expensive machines. Implementation started in 1964 with the arrival of the SDS 930 which was modified slightly, and an operating system was written from scratch. Students who worked on the Berkeley Timesharing System included undergraduates Chuck Thacker and L. Peter Deutsch and doctoral student B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SDS 940
The SDS 940 was Scientific Data Systems' (SDS) first machine designed to directly support time-sharing. The 940 was based on the SDS 930's 24-bit CPU, with additional circuitry to provide protected memory and virtual memory. It was announced in February 1966 and shipped in April, becoming a major part of Tymshare's expansion during the 1960s. The influential Stanford Research Institute "oN-Line System" (NLS) was demonstrated on the system. This machine was later used to run Community Memory, the first bulletin board system. After SDS was acquired by Xerox in 1969 and became Xerox Data Systems, the SDS 940 was renamed as the XDS 940. History The design was originally created by the University of California, Berkeley as part of their Project Genie that ran between 1964 and 1969. Genie added memory management and controller logic to an existing SDS 930 computer to give it page-mapped virtual memory, which would be heavily copied by other designs. The 940 was simply a commerci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM M44/44X
The IBM M44/44X was an experimental computer system from the mid-1960s, designed and operated at IBM's Thomas J. Watson Research Center at Yorktown Heights, New York. It was based on a modified IBM 7044 (the 'M44'), and simulated multiple 7044 virtual machines (the '44X'), using both hardware and software. Key team members were Dave Sayre and Rob Nelson. This was a groundbreaking machine, used to explore paging, the virtual machine concept, and computer performance measurement. It was purely a research system, and was cited in 1981 by Peter Denning as an outstanding example of experimental computer science. The term ''virtual machine'' probably originated with the M44/44X project, from which it was later appropriated by the CP-40 team to replace their earlier term ''pseudo machine''. Unlike CP-40 and later CP/CMS control programs, M44/44X did ''not'' implement a complete simulation of the underlying hardware (i.e. full virtualization). CP-40 project leader Robert Creasy o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University Of Manchester
The University of Manchester is a public university, public research university in Manchester, England. The main campus is south of Manchester city centre, Manchester City Centre on Wilmslow Road, Oxford Road. The University of Manchester is considered a red brick university, a product of the civic university movement of the late 19th century. The current University of Manchester was formed in 2004 following the merger of the University of Manchester Institute of Science and Technology (UMIST) and the Victoria University of Manchester. This followed a century of the two institutions working closely with one another. Additionally, the university owns and operates major cultural assets such as the Manchester Museum, The Whitworth art gallery, the John Rylands Library, the Tabley House, Tabley House Collection and the Jodrell Bank Observatory – a UNESCO World Heritage Site. The University of Manchester Institute of Science and Technology had its origins in the Manchester Mechan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atlas Supervisor
The Atlas Supervisor was the program which managed the allocation of processing resources of Manchester University's Atlas Computer so that the machine was able to act on many tasks and user programs concurrently. Its various functions included running the Atlas computer's virtual memory (Atlas Supervisor paper, section 3, Store Organisation) and is ‘considered by many to be the first recognisable modern operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...’. Brinch Hansen described it as "the most significant breakthrough in the history of operating systems." References ;Notes ;Works cited * * External linksThe Atlas Supervisor paper (T Kilburn, R B Payne, D J Howarth, 1962) 1962 software Discontinued operating systems {{operating-system-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atlas (computer)
The Atlas was one of the world's first supercomputers, in use from 1962 (when it was claimed to be the most powerful computer in the world) to 1972. Atlas's capacity promoted the saying that when it went offline, half of the United Kingdom's computer capacity was lost. It is notable for being the first machine with virtual memory (at that time referred to as "one-level store") using paging techniques; this approach quickly spread, and is now ubiquitous. Atlas was a second-generation computer, using discrete germanium transistors. Atlas was created in a joint development effort among the University of Manchester, Ferranti and Plessey. Two other Atlas machines were built: one for BP and the University of London, and one for the Atlas Computer Laboratory at Chilton near Oxford. A derivative system was built by Ferranti for the University of Cambridge. Called the Titan, or Atlas 2, it had a different memory organisation and ran a time-sharing operating system developed by Camb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferranti
Ferranti International PLC or simply Ferranti was a UK-based electrical engineering and equipment firm that operated for over a century, from 1885 until its bankruptcy in 1993. At its peak, Ferranti was a significant player in power grid systems, defense electronics, and computing, and was once a constituent of the FTSE 100 Index. The company had an extensive presence in the defense sector, manufacturing advanced cockpit displays, radar transmitters, inertial navigation systems, and avionics for military aircraft, including the Tornado fighter jet. It was a pioneer in computer technology, launching the Ferranti Mark 1 in 1951, one of the world's first commercially available computers. Ferranti's global footprint extended beyond the UK, with factories and branch plants in Australia, Canada, Singapore, Germany, and the United States. The company had a strong presence in Edinburgh, with numerous branch-plants as well as an aviation facility. Despite its eventual collapse, some ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fragmentation (computer)
In computer storage, fragmentation is a phenomenon in the computer system which involves the distribution of data in to smaller pieces which storage space, such as computer memory or a hard drive, is used inefficiently, reducing capacity or performance and often both. The exact consequences of fragmentation depend on the specific system of storage allocation in use and the particular form of fragmentation. In many cases, fragmentation leads to storage space being "wasted", and programs will tend to run inefficiently due to the shortage of memory. Basic principle In main memory fragmentation, when a computer program requests blocks of memory from the computer system, the blocks are allocated in chunks. When the computer program is finished with a chunk, it can free it back to the system, making it available to later be allocated again to another or the same program. The size and the amount of time a chunk is held by a program varies. During its lifespan, a computer program can requ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Segmentation
Memory segmentation is an operating system memory management technique of dividing a computer's primary memory into segments or sections. In a computer system using segmentation, a reference to a memory location includes a value that identifies a segment and an offset (memory location) within that segment. Segments or sections are also used in object files of compiled programs when they are linked together into a program image and when the image is loaded into memory. Segments usually correspond to natural divisions of a program such as individual routines or data tables so segmentation is generally more visible to the programmer than paging alone. Segments may be created for program modules, or for classes of memory usage such as code segments and data segments. Certain segments may be shared between programs. Segmentation was originally invented as a method by which system software could isolate software processes ( tasks) and data they are using. It was intended to in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
