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In computer science NOP or NOOP (short for No OPeration) is an assembly language instruction, sequence of programming language statements, or computer protocol command that effectively does nothing at all. NOP can stand for: the NOP assembly language mnemonic. ... Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ... An assembly language is a low-level language for programming computers. ... For other senses of this word, see protocol. ...

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NOP machine instruction

Some computer instruction sets include an instruction whose explicit purpose is not to change the state of any of the programmer accessible registers, status flags or memory, and which may require a specific number of clock cycles to execute. In other instruction sets a NOP has to be simulated by executing an instruction having operands that cause the same effect (e.g., on the SPARC processor the instruction sethi 0,%g0 is the recommended solution). An instruction set is [a list of] all the instructions, and all their variations, that a processor can execute. ... Register or registration may mean: Registration (or licensing) is required of a number of occupations and professions where maintenance of standards is required to protect public safety. ... Look up Status in Wiktionary, the free dictionary. ... Primary storage is a category of computer storage, often called main memory. ... Sun UltraSPARC II Microprocessor Sun UltraSPARC T1 (Niagara 8 Core) SPARC (Scalable Processor Architecture) is a RISC microprocessor instruction set architecture originally designed in 1985 by Sun Microsystems. ...


NOPs are most commonly used for timing purposes, to force memory alignment, to prevent hazards, to occupy a branch delay slot, or as a "place-holder" to be replaced by active instructions later on in program development (or to replace removed instructions when re-factoring would-be problematic or time-consuming code). The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... In computer architecture, a hazard is a potential problem that can happen in a pipelined processor. ... In computer architecture, a branch delay instruction is an instruction immediately following a conditional branch instruction which is executed whether or not the branch is taken. ...


The characteristics of the NOP instruction for the Intel x86 CPU family are: Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... CPU redirects here. ...

For other users of the word/name byte, see byte (disambiguation). ... Microprocessors perform operations using binary bits (on/off/1or0). ... In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ...

NOP code

NOP is sometimes used as a description for the action performed by a function or a sequence of programming language statements. If the function or code has no effect, then it is sometimes called a NOP or NOOP (it might also be called redundant code). A common compiler optimization is the detection and removal of this kind of code. Redundant code is a computer programming term for code that is executed but has no effect on the output of a program (dead code is the term applied to code that is never executed). ... Compiler optimization is the process of tuning the output of a compiler to minimize some attribute (or maximize the efficiency) of an executable program. ...


The following is an example of a single C statement that behaves like a NOP (the issue is whether the statement affects program output, not whether or not a compiler generates any code for this statement): This article is about the computing term. ...

 i+1; 

(This statement performs an addition and discards the result.)


The simplest possible statement in C that behaves like a NOP is the so called null statement; which is just a semi-colon in a context requiring a statement. (A compiler is not required to generate a NOP instruction in this case; typically no instructions whatsoever would be generated.)

 ; 

The null statement is useless by itself, but can have a syntactic use in a wider context, e.g., within the context of a loop:

 while (ReadChar() != 'n') ; 

The above code continues calling the function ReadChar until it returns a n (newline) character.


NOP protocol commands

Many computer protocols, such as telnet, include a NOP command that a client can issue to request a response from the server without requesting any other actions. Such a command can be used to ensure the connection is still alive or that the server is responsive. A NOOP command is part of the following protocols (this is a partial list): For other senses of this word, see protocol. ... For the packet switched network, see Telenet. ... Keepalive is a message sent by one device to another to check that the link between the two is operating. ...

Note that unlike the other protocols listed, the IMAP4 NOP command has a specific purpose which is to allow the client to request that the server send unsolicited information reflecting the actions of other clients. For the packet switched network, see Telenet. ... This article is about the File Transfer Protocol standardised by the IETF. For other file transfer protocols, see File transfer protocol (disambiguation). ... Simple Mail Transfer Protocol (SMTP) is the de facto standard for e-mail transmissions across the Internet. ... The X Window System logo The X Window core protocol[1][2][3] is the base protocol of the X Window System, which is a networked windowing system for bitmap displays used to build graphical user interfaces on Unix, Unix-like, and other operating systems. ... In computing, local e-mail clients use the Post Office Protocol version 3 (POP3), an application-layer Internet standard protocol, to retrieve e-mail from a remote server over a TCP/IP connection. ... The Network News Transfer Protocol or NNTP is an Internet application protocol used primarily for reading and posting Usenet articles, as well as transferring news among news servers. ... In computer networking, the Name/Finger protocol and the Finger user information protocol are simple network protocols for the exchange of human-oriented status and user information. ... The Internet Message Access Protocol (commonly known as IMAP or IMAP4, and previously called Internet Mail Access Protocol, Interactive Mail Access Protocol (RFC 1064), and Interim Mail Access Protocol[1]) is an application layer Internet protocol operating on port 143 that allows a local client to access e-mail on...


While most telnet servers respond to a NOOP command with "OK" or "+OK", some programmers have added quirky responses to noop. Some examples: For the packet switched network, see Telenet. ...

 noop : OK, but why? :) noop : Well, noop to you too! 

Cracking

NOPs are often involved when cracking software that checks for serial numbers, specific hardware or software requirements, presence or absence of hardware dongles, etc. This is accomplished by altering functions and subroutines to by-pass security checks and instead simply return the expected value being checked for. Software cracking is the modification of software to remove protection methods: copy prevention, trial/demo version, serial number, hardware key, CD check or software annoyances like nag screens and adware. ... Chained parallel port copy prevention dongles. ... In computer science, a subroutine (function, method, procedure, or subprogram) is a portion of code within a larger program, which performs a specific task and can be relatively independent of the remaining code. ...


See also

A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... In computer science and more specifically the x86 arthitecture, HLT is an assembly language instruction which halts the CPU until the next external interrupt is fired, often times this is the clock. ... An instruction set is [a list of] all the instructions, and all their variations, that a processor can execute. ... Intel Pentium 4 (Northwood version), one example out of a huge number of x86 implementations from Intel, AMD, and others. ... An identity function f is a function which doesnt have any effect: it always returns the same value that was used as its argument. ... Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. ... Adventure (also known as ADVENT or Colossal Cave) (Crowther & Woods, 1976) was the first computer adventure game. ...

References

  1. ^ Intel Architecture Software Developer's Manual, Volume 2: Instruction Set Reference Manual. Retrieved on 2007-07-13.
Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 194th day of the year (195th in leap years) in the Gregorian calendar. ...

  Results from FactBites:
 
Nop - Esolang (218 words)
A nop (sometimes spelled no-op or noop) is an operation in a programming language that does nothing.
While nops are generally useless in most "serious" programming languages (except very low-level ones like machine language, where they can affect timing), they can come in very valuable in esoteric programming languages, often to allow an arbitrary effect at an arbitrary point.
Many character-based languages, such as Brainfuck, consider unrecognized characters to be nops, which allows them to be used for comments.
NOP Design (230 words)
NOP Design is proud to be part of the Cyberitas family of companies.
NOP Design is proud to announce the release of SIML, v.4.6.
NOP Design helps contribute back to the open source and free software community with several on-going projects.
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