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Page Replacement Algorithms
In a computer operating system that uses paging for virtual memory management, page replacement algorithms decide which memory pages to page out, sometimes called swap out, or write to disk, when a page of memory needs to be allocated. Page replacement happens when a requested page is not in memory (page fault) and a free page cannot be used to satisfy the allocation, either because there are none, or because the number of free pages is lower than some threshold. When the page that was selected for replacement and paged out is referenced again it has to be paged in (read in from disk), and this involves waiting for I/O completion. This determines the ''quality'' of the page replacement algorithm: the less time waiting for page-ins, the better the algorithm. A page replacement algorithm looks at the limited information about accesses to the pages provided by hardware, and tries to guess which pages should be replaced to minimize the total number of page misses, while balancing thi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer
A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as Computer program, programs. These programs enable computers to perform a wide range of tasks. A computer system is a nominally complete computer that includes the Computer hardware, hardware, operating system (main software), and peripheral equipment needed and used for full operation. This term may also refer 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. Simple special-purpose devices like microwave ovens and remote controls are included, as are factory devices like industrial robots and computer-aided design, as well as general-purpose devi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kernel (computer Science)
The kernel is a computer program at the core of a computer's operating system and generally has complete control over everything in the system. It is the portion of the operating system code that is always resident in memory and facilitates interactions between hardware and software components. A full kernel controls all hardware resources (e.g. I/O, memory, cryptography) via device drivers, arbitrates conflicts between processes concerning such resources, and optimizes the utilization of common resources e.g. CPU & cache usage, file systems, and network sockets. On most systems, the kernel is one of the first programs loaded on startup (after the bootloader). It handles the rest of startup as well as memory, peripherals, and input/output (I/O) requests from software, translating them into data-processing instructions for the central processing unit. The critical code of the kernel is usually loaded into a separate area of memory, which is protected from access by applicati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amortized Analysis
In computer science, amortized analysis is a method for analyzing a given algorithm's complexity, or how much of a resource, especially time or memory, it takes to execute. The motivation for amortized analysis is that looking at the worst-case run time can be too pessimistic. Instead, amortized analysis averages the running times of operations in a sequence over that sequence. As a conclusion: "Amortized analysis is a useful tool that complements other techniques such as worst-case and average-case analysis." For a given operation of an algorithm, certain situations (e.g., input parametrizations or data structure contents) may imply a significant cost in resources, whereas other situations may not be as costly. The amortized analysis considers both the costly and less costly operations together over the whole sequence of operations. This may include accounting for different types of input, length of the input, and other factors that affect its performance. History Amortized ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Online Algorithm
In computer science, an online algorithm is one that can process its input piece-by-piece in a serial fashion, i.e., in the order that the input is fed to the algorithm, without having the entire input available from the start. In contrast, an offline algorithm is given the whole problem data from the beginning and is required to output an answer which solves the problem at hand. In operations research, the area in which online algorithms are developed is called online optimization. As an example, consider the sorting algorithms selection sort and insertion sort: selection sort repeatedly selects the minimum element from the unsorted remainder and places it at the front, which requires access to the entire input; it is thus an offline algorithm. On the other hand, insertion sort considers one input element per iteration and produces a partial solution without considering future elements. Thus insertion sort is an online algorithm. Note that the final result of an insertion sort ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
László Bélády
László "Les" Bélády (born April 29, 1928, in Budapest; died November 6, 2021) was a Hungarian computer scientist notable for devising the Bélády's Min theoretical memory caching algorithm in 1966 while working at IBM Research. He also demonstrated the existence of a Bélády's anomaly. During the 1980s, he was the editor-in-chief of the IEEE Transactions on Software Engineering. Education Bélády earned B.S. in Mechanical Engineering, then an M.S. in Aeronautical Engineering at the Technical University of Budapest in 1950. Life and career He left Hungary after the Hungarian Revolution of 1956. Then he worked as a draftsman at Ford Motor Company in Cologne and as an aerodynamics engineer at Dassault in Paris. In 1961, he immigrated to the United States. In the 1960s and 1970s, he primarily lived in New York City with stints in California and England, where he joined International Business Machines and did early work in operating systems, virtual machine architectures, pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clairvoyance
Clairvoyance (; ) is the magical ability to gain information about an object, person, location, or physical event through extrasensory perception. Any person who is claimed to have such ability is said to be a clairvoyant () ("one who sees clearly"). Claims for the existence of paranormal and psychic abilities such as clairvoyance have not been supported by scientific evidence. Carroll, Robert Todd. (2003)"Clairvoyance" Retrieved 2014-04-30. Parapsychology explores this possibility, but the existence of the paranormal is not accepted by the scientific community. The scientific community widely considers parapsychology, including the study of clairvoyance, a pseudoscience. Usage Pertaining to the ability of clear-sightedness, clairvoyance refers to the paranormal ability to see persons and events that are distant in time or space. It can be divided into roughly three classes: precognition, the ability to perceive or predict future events, retrocognition, the ability to see pa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prefetch Input Queue
Fetching the instruction opcodes from program memory well in advance is known as prefetching and it is served by using prefetch input queue (PIQ).The pre-fetched instructions are stored in data structure - namely a queue. The fetching of opcodes well in advance, prior to their need for execution increases the overall efficiency of the processor boosting its speed. The processor no longer has to wait for the memory access operations for the subsequent instruction opcode to complete. This architecture was prominently used in the Intel 8086 microprocessor. Introduction Pipelining was brought to the forefront of computing architecture design during the 1960s due to the need for faster and more efficient computing. Pipelining is the broader concept and most modern processors load their instructions some clock cycles before they execute them. This is achieved by pre-loading machine code from memory into a ''prefetch input queue''. This behavior only applies to von Neumann computer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Demand Paging
In computer operating systems, demand paging (as opposed to anticipatory paging) is a method of virtual memory management. In a system that uses demand paging, the operating system copies a disk page into physical memory only if an attempt is made to access it and that page is not already in memory (''i.e.'', if a page fault occurs). It follows that a process begins execution with none of its pages in physical memory, and many page faults will occur until most of a process's working set of pages are located in physical memory. This is an example of a lazy loading technique. Basic concept Demand paging follows that pages should only be brought into memory if the executing process demands them. This is often referred to as lazy evaluation as only those pages demanded by the process are swapped from secondary storage to main memory. Contrast this to pure swapping, where all memory for a process is swapped from secondary storage to main memory during the process startup. Commonly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Full Duplex
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Page Table
A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. Virtual addresses are used by the program executed by the accessing process, while physical addresses are used by the hardware, or more specifically, by the random-access memory (RAM) subsystem. The page table is a key component of virtual address translation that is necessary to access data in memory. Role of the page table In operating systems that use virtual memory, every process is given the impression that it is working with large, contiguous sections of memory. Physically, the memory of each process may be dispersed across different areas of physical memory, or may have been moved ( paged out) to secondary storage, typically to a hard disk drive (HDD) or solid-state drive (SSD). When a process requests access to data in its memory, it is the responsibility of the operating system to map the virtual addres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Management (operating Systems)
In operating systems, memory management is the function responsible for managing the computer's primary memory. The memory management function keeps track of the status of each memory location, either ''allocated'' or ''free''. It determines how memory is allocated among competing processes, deciding which gets memory, when they receive it, and how much they are allowed. When memory is allocated it determines which memory locations will be assigned. It tracks when memory is freed or ''unallocated'' and updates the status. This is distinct from application memory management, which is how a process manages the memory assigned to it by the operating system. Memory management techniques Single contiguous allocation ''Single allocation'' is the simplest memory management technique. All the computer's memory, usually with the exception of a small portion reserved for the operating system, is available to a single application. MS-DOS is an example of a system that allocates memory i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solaris (operating System)
Solaris is a proprietary Unix operating system originally developed by Sun Microsystems. After the Sun acquisition by Oracle in 2010, it was renamed Oracle Solaris. Solaris superseded the company's earlier SunOS in 1993, and became known for its scalability, especially on SPARC systems, and for originating many innovative features such as DTrace, ZFS and Time Slider. Solaris supports SPARC and x86-64 workstations and servers from Oracle and other vendors. Solaris was registered as compliant with the Single UNIX Specification until 29 April 2019. Historically, Solaris was developed as proprietary software. In June 2005, Sun Microsystems released most of the codebase under the CDDL license, and founded the OpenSolaris open-source project. With OpenSolaris, Sun wanted to build a developer and user community around the software. After the acquisition of Sun Microsystems in January 2010, Oracle decided to discontinue the OpenSolaris distribution and the development model. In Aug ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
