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Overlay (programming)
In a general computing sense, overlaying means "the process of transferring a Block (data storage), block of program code or other data into main memory, replacing what is already stored". Overlaying is a computer programming, programming method that allows programs to be larger than the computer's main memory. An embedded system would normally use overlays because of the limitation of physical memory, which is internal memory for a system-on-chip, and the lack of virtual memory facilities. Usage Constructing an overlay program involves manually dividing a program into self-contained object code blocks called overlays or links, generally laid out in a tree structure. ''Sibling'' segments, those at the same depth level, share the same memory, called ''overlay region'' or ''destination region''. An overlay manager, either part of the operating system or part of the overlay program, loads the required overlay from Auxiliary memory, external memory into its destination region when i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Overlay Programming
Overlay may refer to: Computers *Overlay network, a computer network which is built on top of another network *Video overlay, techniques to display video on computer display *Hardware overlay, one type of video overlay that uses memory dedicated to the application *Another term for exec (system call), exec, replacing one process by another *Overlay (programming), a technique to reduce the amount of memory used by a program *Overlay keyboard, a specialized keyboard with no pre-set keys *Keyboard overlay, a sheet of printed text sitting between the keys, depicting an alternate keyboard layout *Vector overlay, an analysis procedure in a geographic information system for integrating multiple data sets Other uses *Overlay architecture, temporary elements that supplement existing buildings and infrastructure for major sporting events or festivals *Overlay complex, a method of introducing new area codes in telephony *Overlay control, in semiconductor manufacturing, for monitoring layer-to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Working Set
Working set is a concept in computer science which defines the amount of memory that a process (computing), process requires in a given time interval. Definition Peter_J._Denning, Peter Denning (1968) defines "the working set of information W(t, \tau) of a process (computing), process at time t to be the collection of information referenced by the process during the process time interval (t - \tau, t)". Typically the units of information in question are considered to be page (computer memory), memory pages. This is suggested to be an approximation of the set of pages that the process will access in the future (say during the next \tau time units), and more specifically is suggested to be an indication of what pages ought to be kept in main memory to allow most progress to be made in the execution of that process. Rationale The effect of the choice of what pages to be kept in main memory (as distinct from being ''paged out'' to auxiliary storage) is important: if too many pages o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Job
Chain loading is a method used by computer programs to replace the currently executing program with a new program, using a common data area to pass information from the current program to the new program. It occurs in several areas of computing. Chain loading is similar to the use of overlays. Unlike overlays, however, chain loading replaces the currently executing program in its entirety. Overlays usually replace only a portion of the running program. Like the use of overlays, the use of chain loading increases the I/O load of an application. Chain loading in boot manager programs In operating system boot manager programs, chain loading is used to pass control from the boot manager to a boot sector. The target boot sector is loaded in from disk, replacing the in-memory boot sector from which the boot manager itself was bootstrapped, and executed. Chain loading in Unix In Unix (and in Unix-like operating systems), the exec() system call is used to perform chain loading ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Library (computing)
In computing, a library is a collection of System resource, resources that can be leveraged during software development to implement a computer program. Commonly, a library consists of executable code such as compiled function (computer science), functions and Class (computer programming), classes, or a library can be a collection of source code. A resource library may contain data such as images and Text string, text. A library can be used by multiple, independent consumers (programs and other libraries). This differs from resources defined in a program which can usually only be used by that program. When a consumer uses a library resource, it gains the value of the library without having to implement it itself. Libraries encourage software reuse in a Modular programming, modular fashion. Libraries can use other libraries resulting in a hierarchy of libraries in a program. When writing code that uses a library, a programmer only needs to know how to use it not its internal d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coupling (computer Science)
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. In a more general context, a coupling can also be a mechanical device that serves to connect the ends of adjacent parts or objects. Couplings do not normally allow disconnection of shafts during operation, however there are torque-limiting couplings which can slip or disconnect when some torque limit is exceeded. Selection, installation and maintenance of couplings can lead to reduced maintenance time and maintenance cost. Uses Shaft couplings are used in machinery for several purposes. A primary function is to transfer power from one end to another end (ex: motor transfer power to pump through coupling). Other common uses: * To alter the vibration characteristics of rotating units * To connect the driving and the driven ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Codec
A codec is a computer hardware or software component that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or data stream, and hence is a type of codec. ''Endec'' is a portmanteau of encoder/decoder. A coder or encoder encodes a data stream or a signal for transmission or storage, possibly in encrypted form, and the decoder function reverses the encoding for playback or editing. Codecs are used in videoconferencing, streaming media, and video editing applications. History Originally, in the mid-20th century, a codec was a hardware device that coded analog signals into digital form using pulse-code modulation (PCM). Later, the term was also applied to software for converting between digital signal formats, including companding functions. Examples An audio codec converts analog audio signals into digital signals for transmissi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software Componentry
Component-based software engineering (CBSE), also called component-based development (CBD), is a style of software engineering that aims to construct a software system from components that are loosely-coupled and reusable. This emphasizes the separation of concerns among components. To find the right level of component granularity, software architects have to continuously iterate their component designs with developers. Architects need to take into account user requirements, responsibilities and architectural characteristics. Considerations For large-scale systems developed by large teams, a disciplined culture and process is required to achieve the benefits of CBSE. Third-party components are often utilized in large systems. The system can be designed visually with the Unified Modeling Language (UML). Each component is shown as a rectangle, and an interface is shown as a lollipop to indicate a provided interface and as a socket to indicate consumption of an interface. Comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space Shuttle
The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program name was the Space Transportation System (STS), taken from the 1969 plan led by U.S. vice president Spiro Agnew for a system of reusable spacecraft where it was the only item funded for development. The first (STS-1) of four orbital test flights occurred in 1981, leading to operational flights (STS-5) beginning in 1982. Five complete Space Shuttle orbiter vehicles were built and flown on a total of 135 missions from 1981 to 2011. They launched from the Kennedy Space Center (KSC) in Florida. Operational missions launched numerous satellites, interplanetary probes, and the Hubble Space Telescope (HST), conducted science experiments in orbit, participated in the Shuttle–Mir program, Shuttle-''Mir'' program with Russia, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paging
In computer operating systems, memory paging is a memory management scheme that allows the physical Computer memory, 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 (computer memory), ''page frames'' and storing pages on and retrieving them from Computer data storage#Secondary storage, 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 Virtual memory#Paged virtual memory, ''paged virtual memory''. In this scheme, the operating system retrieves data from secondary storage in Block (data storage), blocks of the same size (pages). Paging is an important part of virtual memory implementations in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Real-time Computing
Real-time computing (RTC) is the computer science term for Computer hardware, hardware and software systems subject to a "real-time constraint", for example from Event (synchronization primitive), event to Event (computing), system response. Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines".Mordechai Ben-Ari, Ben-Ari, Mordechai; "Principles of Concurrent and Distributed Programming", ch. 16, Prentice Hall, 1990, , p. 164 The term "real-time" is also used in Computer simulation, simulation to mean that the simulation's clock runs at the same speed as a real clock. Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds. A system not specified as operating in real time cannot usually ''guarantee'' a response within any timeframe, although ''typical'' or ''expected'' response times may be given. Real-time processing ''fails'' if not completed within a specified deadline rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Management Unit
A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit that examines all references to computer memory, memory, and translates the memory addresses being referenced, known as virtual memory addresses, into physical addresses in main memory. In modern systems, programs generally have addresses that access the theoretical maximum memory of the computer architecture, 32 or 64 bits. The MMU maps the addresses from each program into separate areas in physical memory, which is generally much smaller than the theoretical maximum. This is possible because programs rarely use large amounts of memory at any one time. Most modern operating systems (OS) work in concert with an MMU to provide virtual memory (VM) support. The MMU tracks memory use in fixed-size blocks known as ''pages''. If a program refers to a location in a page that is not in physical memory, the MMU sends an interrupt to the operating system. The OS selects a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
