In computing Computing, also known as computer science, is usually defined as the activity of using and improving computer technology, computer hardware and software. It is the computer-specific part of information technology. Computer science is the study and the science of the theoretical foundations of information and computation and their implementation, a logical address is the address at which an item (memory cell, storage element, network host) appears to reside from the perspective of an executing application program Application software is computer software designed to help the user perform a particular task. Such programs are also called software applications, applications or apps. Typical examples are word processors, spreadsheets, media players and database applications.
A logical address may be different from the physical address In computing, a physical address, also real address, or binary address, is the memory address that is electronically presented on the computer address bus circuitry in order to enable the data bus to access a particular storage cell of main memory due to the operation of an address translator or mapping function. Such mapping functions may be, in the case of a computer memory architecture, a memory management unit A memory management unit , sometimes called paged memory management unit (PMMU), is a computer hardware component responsible for handling accesses to memory requested by the central processing unit (CPU). Its functions include translation of virtual addresses to physical addresses (i.e., virtual memory management), memory protection, cache (MMU) between the CPU The Central Processing Unit or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPUs have changed and the memory bus, or an address translation layer, e.g., the Data Link Layer The Data Link Layer is Layer 2 of the seven-layer OSI model of computer networking. It corresponds to or is part of the link layer of the TCP/IP reference model, between the hardware and the internetworking protocols (Internet Protocol The Internet Protocol is a protocol used for communicating data across a packet-switched internetwork using the Internet Protocol Suite, also referred to as TCP/IP) in a computer networking system.
Computer memory
The physical address of computer memory banks may be mapped to different logical addresses for various purposes.
For example, the same physical memory may appear at two different logical addresses and if accessed by the program at one address, data will pass through the processor cache In computer science, a cache is a component that improves performance by transparently storing data such that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere. If requested data is contained in the whereas if it is accessed at the other address, it will bypass the cache.
In a system supporting virtual memory Virtual memory is an integral part of a computer architecture; all implementations require hardware support, typically in the form of a memory management unit built into the CPU. Consequently, older operating systems (such as DOS of the 1980s or those for the mainframes of the 1960s) generally have no virtual memory functionality, though notable, there may actually not be any physical memory mapped to a logical address until an access is attempted. The access triggers special functions of the operating system which reprogram the MMU to map the address to some physical memory, perhaps writing the old contents of that memory to disk and reading back from disk what the memory should contain at the new logical address. In this case, the logical address may be referred to as a virtual address.
Other Uses
Logical address or virtual address is also used in IBM's International Business Machines (NYSE: IBM) is a multinational computer, technology and IT consulting corporation headquartered in Armonk, North Castle, New York, United States. IBM is the world's fourth largest technology company and the second most valuable by global brand (after Coca-Cola). IBM is one of the few information technology companies VM operating system and in Virtual Device Location.
See also
- Memory segment
- Flat memory model
- memory address In computer science, a memory address is an identifier for a memory location, at which a computer program or a hardware device can store data and later retrieve it. Generally this is a binary number from a finite monotonically ordered sequence that uniquely describes the memory itself
This article was originally based on material from the Free On-line Dictionary of Computing The Free On-line Dictionary of Computing is an online, searchable, encyclopedic dictionary of computing subjects. It was founded in 1985 by Denis Howe and is hosted by Imperial College London. Howe has served as the editor-in-chief since the dictionary's inception, with visitors to the website able to make suggestions for additions or corrections, which is licensed under the GFDL The GNU Free Documentation License is a copyleft license for free documentation, designed by the Free Software Foundation (FSF) for the GNU Project. It is similar to the GNU General Public License, giving readers the rights to copy, redistribute, and modify a work and requires all copies and derivatives to be available under the same license.
Categories: Virtual memory
