NOP

: For other meanings of NOP, see NOP (disambiguation)

NOP or NOOP (short for No OPeration ) is an assembly language instruction, sequence of programming language statements, or protocol (computing) command that does nothing at all.

= NOP Machine Instruction =

Most computer instruction sets include an instruction that does nothing for a specific number of clock cycles; it makes no changes to main memory or computer program status. NOPs are most commonly used for timing purposes, to force memory alignment, to prevent hazard (computer architecture)s, to occupy a branch delay slot, or as a place-holder to be replaced by active instructions later on in program development. The characteristics of the NOP instruction for the Intel x86 central processing unit family are:

Mnemonic: NOP

Clock cycles: 3

Bytes: 1

90

In the MOS Technology 6502 and MOS Technology 6510 processors, NOP has the opcode 0xEA. The Motorola 68000 processor s NOP instruction has the opcode 0x4E71.

= NOOP code =

NOOP can also be used as a description for what a function or sequence of programming language statements does. If the function or code has no net effect, then it could be called a noop. An example in the C programming language could be as follows:

i++; i--;

Today, optimizing compilers search for noop statements and code. As the function or piece of code does nothing, the compiler simply removes it. Many optimizing compilers include a directive by which a programmer can explicitly disable this optimization, thereby including code that might appear to be a noop, for cases in which removing it would cause a bug.

= NOOP Protocol Commands =

Many protocol (computing)s, such as Telnet, include a NOOP 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 ):

Telnet

File Transfer Protocol

Simple Mail Transfer Protocol

Post Office Protocol

Network News Transfer Protocol

finger

Internet Message Access Protocol

Note that unlike the other protocols listed, the IMAP4 NOOP 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.

While most Telnet servers respond to a NOOP command with OK or +OK , some programmers have added quirky responses to noop. Some examples:

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