OS-ASSEMBLER

Definition -

An assembler is a program that takes basic computer instructions and converts them into a pattern of  bits that the computer's processor can use to perform its basic operations.
It is a computer program to translate between lower-level representations of computer programs.


Typically a modern assembler creates object code by translating assembly instruction mnemonics into opcodes, and by resolving symbolic names for memory locations and other entities^.
The use of symbolic references is a key feature of assemblers, saving tedious calculations and manual address updates after program modifications. Most assemblers also include macro facilities for performing textual substitution—e.g., to generate common short sequences of instructions as inline, instead of called subroutines.
Assemblers are generally simpler to write than compilers for high-level languages, and have been available since the 1950s. Modern assemblers, especially for RISC architectures, such as SPARC or POWER, as well as x86 and x86-64, optimize Instruction scheduling to exploit the CPU pipeline efficiently.

A program written in assembly language consists of a series of mnemonic statements and meta-statements (known variously as directives, pseudo-instructions and pseudo-ops), comments and data. These are translated by an assembler to a stream of executable instructions that can be loaded into memory and executed. Assemblers can also be used to produce blocks of data, from formatted and commented source code, to be used by other code.