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, an address space defines a range of discrete addresses, each of which may correspond to a physical or virtual memory register In computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage available elsewhere. Typically, this specialized storage is not considered part of the normal memory range for the machine. Most, but not all, modern computers adopt the so-called load-store, a network host In communication networks, a node is a connection point, either a redistribution point or a communication endpoint (some terminal equipment). The definition of a node depends on the network and protocol layer referred to. A physical network node is an active electronic device that is attached to a network, and is capable of sending, receiving, or, peripheral device A peripheral is a device attached to a host computer but not part of it whose primary functionality is dependent upon the host, and can therefore be considered as expanding the host's capabilities, while not forming part of the system's core architecture, disk sector In the context of computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of data. The typical formatting of these media provides space for 512 bytes (for magnetic disks) or 2048 bytes (for optical discs) of user-accessible data per sector, or other logical or physical entity. The Internet Assigned Numbers Authority (IANA)[1] allocates ranges of numbers to various registries in order to enable them to each manage their particular address space.
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Overview
Address spaces are created by combining enough uniquely identified qualifiers to make an address unambiguous. For a person's physical address, the address space would be a combination of locations, such as a neighborhood, town, city, or country. Components of an address space may be the same but unless all are identical, the locations will be different. An example could be that there are multiple buildings at the same address of "32 Main Street" but in different towns. Or in the same town but different states. An example of how address spaces work in computing is Internet domains, where the same filename, say, "index.html" can be unique even though it is resident on millions of domains.
Examples
Example address spaces:
- House numbers in street addresses
- Street addresses in towns
- Main memory (physical memory)
- 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
- I/O port space
- Network A computer network, often simply referred to as a network, is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Networks may be classified according to a wide variety of characteristics. This article provides a general addresses
- IP addresses An Internet Protocol address is a numerical label that is assigned to devices participating in a computer network, that uses the Internet Protocol for communication between its nodes. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A in particular
- Domain Name System The Domain Name System is a hierarchical naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participants. Most importantly, it translates domain names meaningful to humans into the numerical (binary) identifiers
- The cylinder-head-sector Cylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true scheme for hard drives
Address translation
In general, things in one address space are physically in a different location than things in another address space. For example, "house number 101 South" on one particular southward street is completely different from any house number (not just the 101st house) on a different southward street.
However, sometimes different address spaces overlap (some physical location exists in both address spaces). When overlapping address spaces are not aligned, translation is necessary. For example, virtual-to-physical address translation is necessary to translate addresses in the virtual memory address space to addresses in physical address space — one physical address, and one or more numerically different virtual addresses, all refer to the same physical byte of RAM Random-access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). "Random" refers to the idea that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the.
Memory models
Many programmers prefer to use a flat memory model, in which there is no distinction between code Machine code or machine language is a system of instructions and data executed directly by a computer's central processing unit. Machine code may be regarded as a primitive programming language or as the lowest-level representation of a compiled and/or assembled computer program. Programs in interpreted languages are not represented by machine space, data In computer science, data is anything in a form suitable for use with a computer. Data is often distinguished from programs. A program is a set of instructions that detail a task for the computer to perform. In this sense, data is thus everything that is not program code space, and 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 — in other words, numerically identical pointers refer to exactly the same byte of RAM in all three address spaces.
However, many early computers did not support a flat memory model — in particular, Harvard architecture The Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape and data in electro-mechanical counters. These early machines had limited data storage, entirely contained machines force program storage to be completely separate from data storage. Many modern DSPs A digital signal processor is a specialized microprocessor with an optimized architecture for the fast operational needs of digital signal processing (such as the Motorola 56000 The Motorola DSP56000 is a family of digital signal processor (DSP) chips produced by Motorola Semiconductor (now known as Freescale Semiconductor) starting in the 1980s and is still being produced in more advanced models in the 2000s. The 56k series was quite popular for a time in a number of computers, including the NeXT, Atari Falcon, and SGI) have 3 separate storage areas — program storage, coefficient storage, and data storage. Some commonly-used instructions fetch from all three areas simultaneously — fewer storage areas (even if there were the same total bytes of storage) would make those instructions run slower.
Memory models in x86 architecture
Early x86 computers used addresses based on a combination of two numbers: a memory segment, and an offset In computer science, an offset within an array or other data structure object is an integer indicating the distance from the beginning of the object up until a given element or point, presumably within the same object. The concept of a distance is valid only if all elements of the object are the same size (typically given in bytes or words) within that segment. Some segments were implicitly treated as code segments, dedicated for instructions In computer science, an instruction is a single operation of a processor defined by an instruction set architecture. In a broader sense, an "instruction" may be any representation of an element of an executable program, such as a bytecode, stack In computer science, a call stack is a dynamic stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, control stack, function stack, or run-time stack, and is often shortened to just "the stack" segments, or normal data In computer science, data is anything in a form suitable for use with a computer. Data is often distinguished from programs. A program is a set of instructions that detail a task for the computer to perform. In this sense, data is thus everything that is not program code segments. Although the usages were different, the segments did not have different memory protections Memory protection is a way to control memory access rights on a computer, and is a part of most modern operating systems. The main purpose of memory protection is to prevent a process from accessing memory that has not been allocated to it. This prevents a bug within a process from affecting other processes, or the operating system itself. Memory reflecting this.
Now, many programmers prefer to use a flat memory model, in which all segments (segment registers) are generally set to zero, and only offsets are variable.
References
- ^ "IPv4 Address Space Registry" (in English). Internet Assigned Numbers Authority (IANA). March 11, 2009. http://www.iana.org/assignments/ipv4-address-space/. Retrieved 2009-03-15.
Categories: Computer memory Categories: Digital media | Computer hardware | Computer data | Computer storage | Computer architecture | Memory management This category covers software which manages the access and allocation of main memory. This includes real memory and the subcategory for virtual memory
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