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Assembler ○꠹｜Definition｜1st｜20260723001742-00-⌔
Assembly language - Wikipedia#Assembler
Assembler
An assembler program creates object code by translating combinations of mnemonics and syntax for operations and addressing modes into their numerical equivalents. This representation typically includes an operation code (“opcode”) as well as other control bits and data. The assembler also calculates constant expressions and resolves symbolic names for memory locations and other entities.1 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.
Some assemblers may also be able to perform some simple types of instruction set -specific optimizations. One concrete example of this may be the ubiquitous x86 assemblers from various vendors. Called jump-sizing,1 most of them are able to perform jump-instruction replacements (long jumps replaced by short or relative jumps) in any number of passes, on request. Others may even do simple rearrangement or insertion of instructions, such as some assemblers for RISC architectures that can help optimize a sensible instruction scheduling to exploit the CPU pipeline as efficiently as possible.2
Assemblers have been available since the 1950s, as the first step above machine language and before high-level programming languages such as Fortran, Algol, COBOL and Lisp. There have also been several classes of translators and semi-automatic code generators with properties similar to both assembly and high-level languages, with Speedcode as perhaps one of the better-known examples.
There may be several assemblers with different syntax for a particular CPU or instruction set architecture. For instance, an instruction to add memory data to a register in a x86 -family processor might be
add eax,[ebx], in original Intel syntax, whereas this would be writtenaddl (%ebx),%eaxin the AT&T syntax used by the GNU Assembler. Despite different appearances, different syntactic forms generally generate the same numeric machine code. A single assembler may also have different modes in order to support variations in syntactic forms as well as their exact semantic interpretations (such as FASM -syntax, TASM -syntax, ideal mode, etc., in the special case of x86 assembly programming).Printed 2026-07-23.
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Link to original Footnotes
Salomon, David (February 1993) [1992]. Written at California State University, Northridge, California, US. Chivers, Ian D. (ed.). Assemblers and Loaders (PDF). Ellis Horwood Series In Computers And Their Applications (1 ed.). Chicester, West Sussex, UK: Ellis Horwood Limited/Simon & Schuster International Group. pp. 7, 237–238. ISBN 0-13-052564-2. Archived (PDF) from the original on 2020-03-23. Retrieved 2008-10-01. (xiv+294+4 pages) ↩ ↩2
Finlayson, Ian; Davis, Brandon; Gavin, Peter; Uh, Gang-Ryung; Whalley, David; Själander, Magnus; Tyson, Gary (2013). “Improving processor efficiency by statically pipelining instructions”. Proceedings of the 14th ACM SIGPLAN/SIGBED conference on Languages, compilers and tools for embedded systems. pp. 33–44. doi:10.1145/2465554.2465559. ISBN 9781450320856. S2CID 8015812. ↩
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