FACTOID # 17: Though Rhode Island is the smallest state in total area, it has the longest official name: The State of Rhode Island and Providence Plantations.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Assembly language

An assembly language is a low-level language for programming computers. It implements a symbolic representation of the numeric machine codes and other constants needed to program a particular CPU architecture. This representation is usually defined by the hardware manufacturer, and is based on abbreviations (called mnemonics) that help the programmer remember individual instructions, registers, etc. An assembly language is thus specific to a certain physical or virtual computer architecture (as opposed to most high-level languages, which are portable). In computer science, a low-level programming language is a language that provides little or no abstraction from a computers microprocessor. ... Machine code or machine language is a system of instructions and data directly executed by a computers central processing unit. ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... For other uses, see Mnemonic (disambiguation). ... In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. ... A high-level programming language is a programming language that is more user-friendly, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ... In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed (e. ...


Assembly languages were first developed in the 1950s, when they were referred to as second generation programming languages. They eliminated much of the error-prone and time-consuming first-generation programming needed with the earliest computers, freeing the programmer from tedium such as remembering numeric codes and calculating addresses. They were once widely used for all sorts of programming. However, by the 1980s (1990s on small computers), their use had largely been supplanted by high-level languages, in the search for improved programming productivity. Today, assembly language is used primarily for direct hardware manipulation, access to specialized processor instructions, or to address critical performance issues. Typical uses are device drivers, low-level embedded systems, and real-time systems. A second-generation programming language is a term usually used to refer to some form of assembly language. ... A first-generation programming language is a machine-level programming language. ... A high-level programming language is a programming language that is more user-friendly, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ... Programming productivity refers to a variety of software development issues and methodologies affecting the quantity and quality of code produced by an individual or team. ... A device driver, often called a driver for short, is a computer program that enables another program (typically, an operating system) to interact with a hardware device. ... What is an Embedded System? Electronic devices that incorporate a computer(usually a microprocessor) within their implementation. ... Realtime redirects here. ...


A utility program called an assembler is used to translate assembly language statements into the target computer's machine code. The assembler performs a more or less isomorphic translation (a one-to-one mapping) from mnemonic statements into machine instructions and data. (This is in contrast with high-level languages, in which a single statement generally results in many machine instructions. A compiler, analogous to an assembler, is used to translate high-level language statements into machine code; or an interpreter executes statements directly.) In computing, a utility program is a computer program that is in general support of the operations and processes of a computer. ... In mathematics, an isomorphism (in Greek isos = equal and morphe = shape) is a kind of mapping between objects, devised by Eilhard Mitscherlich, which shows a relation between two properties or operations. ... For other uses, see Mnemonic (disambiguation). ... A high-level programming language is a programming language that is more user-friendly, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ... A diagram of the operation of a typical multi-language, multi-target compiler. ... In computer science, an interpreter is a computer program that executes, or performs, instructions written in a computer programming language. ...


Many sophisticated assemblers offer additional mechanisms to facilitate program development, control the assembly process, and aid debugging. In particular, most modern assemblers include a macro facility (described below), and are called macro assemblers. Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware thus making it behave as expected. ... For other uses, see Macro (disambiguation) A macro in computer science is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure. ...

Contents

Key concepts

Assembler

Compare with: Microassembler.

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.[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 to run inline, instead of in a subroutine. A microassembler is a type of software used to design the control unit of a computer. ... In computer science, object file or object code is an intermediate representation of code generated by a compiler after it processes a source code file. ... Microprocessors perform operations using binary bits (on/off/1or0). ... Identifiers (IDs) are lexical tokens that name entities. ... For other uses, see Macro (disambiguation) A macro in computer science is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure. ... In-line expansion or inlining for short is a compiler optimization which expands a function call site into the actual implementation of the function which is called, rather than each call transferring control to a common piece of code. ... 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. ...


Assemblers are generally simpler to write than compilers for high-level languages, and have been available since the 1950s. Modern assemblers, especially for RISC based architectures, such as MIPS, Sun SPARC and HP PA-RISC, optimize instruction scheduling to exploit the CPU pipeline efficiently. A diagram of the operation of a typical multi-language, multi-target compiler. ... A high-level programming language is a programming language that is more user-friendly, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ... The 1950s decade refers to the years 1950 to 1959 inclusive. ... Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ... A MIPS R4400 microprocessor made by Toshiba. ... 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. ... PA-RISC is a microprocessor architecture developed by Hewlett-Packards Systems & VLSI Technology Operation. ... In computer science, instruction scheduling is a compiler optimization used to improve instruction-level parallelism, which improves performance on machines with instruction pipelines. ... A pipeline is a conduit made from pipes connected end-to-end, used mostly to transport fluids like water or petroleum over long distances. ...


More sophisticated high-level assemblers provide language abstractions such as: For Randall Hydes language see High Level Assembly. ...

  • Advanced control structures
  • High-level procedure/function declarations and invocations
  • High-level abstract data types, including structures/records, unions, classes, and sets
  • Sophisticated macro processing
  • Object-Oriented features such as encapsulation, polymorphism, inheritance, interfaces

See Language design below for more details.


Note that, in normal professional usage, the term assembler is often used ambiguously: It is frequently used to refer to an assembly language itself, rather than to the assembler utility. Thus: "CP/CMS was written in S/360 assembler" as opposed to "ASM-H was a widely-used S/370 assembler." The IBM System/360 (S/360) is a computer system family announced by International Business Machines on April 7, 1964. ... The System/370 is a model range of IBM mainframes introduced in the early 1970s as the successors to the System/360 family. ...


Assembly language

A program written in assembly language consists of a series of instructions mnemonics that correspond to a stream of executable instructions, when translated by an assembler, that can be loaded into memory and executed. An assembly language is a low-level language for programming computers. ...


For example, an x86/IA-32 processor can execute the following binary instruction as expressed in machine language: x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... It has been suggested that this article or section be merged with X86 assembly language. ... A system of codes directly understandable by a computers CPU is termed this CPUs native or machine language. ...

  • Binary: 10110000 01100001 (Hexadecimal: B0 61)

The equivalent assembly language representation is easier to remember (more mnemonic): For other uses, see Mnemonic (disambiguation). ...

  • mov al,61h

This instruction means:

The mnemonic "mov" represents the opcode 1011 which moves the value in the second operand into the register indicated by the first operand. The mnemonic was chosen by the instruction set designer to abbreviate "move", making it easier for the programmer to remember. A comma-separated list of arguments or parameters follows the opcode; this is a typical assembly language statement. For other uses, see Decimal (disambiguation). ... 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. ... In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. ...


In practice many programmers drop the word mnemonic and, technically incorrectly, call "mov" an opcode. When they do this they are referring to the underlying binary code which it represents. To put it another way, a mnemonic such as "mov" is not an opcode, but as it symbolizes an opcode, one might refer to "the opcode mov" for example when one intends to refer to the binary opcode it symbolizes rather than to the symbol--the mnemonic--itself. As few modern programmers have need to be mindful of actually what binary patterns are the opcodes for specific instructions, the distinction has in practice become a bit blurred among programmers but not among processor designers.


Transforming assembly into machine language is accomplished by an assembler, and the reverse by a disassembler. Unlike in high-level languages, there is usually a one-to-one correspondence between simple assembly statements and machine language instructions. However, in some cases, an assembler may provide pseudoinstructions which expand into several machine language instructions to provide commonly needed functionality. For example, for a machine that lacks a "branch if greater or equal" instruction, an assembler may provide a pseudoinstruction that expands to the machine's "set if less than" and "branch if zero (on the result of the set instruction)". Most full-featured assemblers also provide a rich macro language (discussed below) which is used by vendors and programmers to generate more complex code and data sequences. An assembly language is a low-level language for programming computers. ... A disassembler is a computer program that translates machine language into assembly language — the inverse operation to that of an assembler. ... A high-level programming language is a programming language that is more user-friendly, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ... In mathematics, a bijection, bijective function, or one-to-one correspondence is a function that is both injective (one-to-one) and surjective (onto), and therefore bijections are also called one-to-one and onto. ... For other uses, see Macro (disambiguation) A macro in computer science is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure. ...


Every computer architecture has its own machine language. On this level, each instruction is simple enough to be executed using a relatively small number of electronic circuits. Computers differ by the number and type of operations they support. For example, a new 64-bit machine would have different circuitry than a 32-bit machine. They may also have different sizes and numbers of registers, and different representations of data types in storage. While most general-purpose computers are able to carry out essentially the same functionality, the ways they do so differ; the corresponding assembly languages reflect these differences. 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). ...


Multiple sets of mnemonics or assembly-language syntax may exist for a single instruction set, typically instantiated in different assembler programs. In these cases, the most popular one is usually that supplied by the manufacturer and used in its documentation. For other uses, see Mnemonic (disambiguation). ...


Language design

Basic elements

Instructions (statements) in assembly language are generally very simple, unlike those in high-level languages. Each instruction typically consists of an operation or opcode plus zero or more operands. Most instructions refer to a single value, or a pair of values. Generally, an opcode is a symbolic name for a single executable machine language instruction. Operands can be either immediate (typically one byte values, coded in the instruction itself) or the addresses of data located elsewhere in storage. This is determined by the underlying processor architecture: the assembler merely reflects how this architecture works. A high-level programming language is a programming language that, in comparison to low-level programming languages, may be more abstract, easier to use, or more portable across platforms. ... In mathematics, an operand is one of the inputs of an operator. ...


Most assemblers also support pseudo-operations, which are directives obeyed by the assembler at assembly time instead of the CPU at run time. (For example, pseudo-ops would be used to reserve storage areas and optionally set their initial contents.) The names of pseudo-ops often start with a dot to distinguish them from machine instructions.


Some assemblers also support pseudo-instructions, which generate two or more machine instructions.


Symbolic assemblers allow programmers to associate arbitrary names (labels or symbols) with memory locations. Usually, every constant and variable is given a name so instructions can reference those locations by name, thus promoting self-documenting code. In executable code, the name of each subroutine is associated with its entry point, so any calls to a subroutine can use its name. Inside subroutines, GOTO destinations are given labels. Some assemblers support local symbols which are lexically distinct from normal symbols (e.g., the use of "10$" as a GOTO destination). GOTO is a statement found in many computer programming languages. ...


Most assemblers provide flexible symbol management, allowing programmers to manage different namespaces, automatically calculate offsets within data structures, and assign labels that refer to literal values or the result of simple computations performed by the assembler. Labels can also be used to initialize constants and variables with relocatable addresses. A namespace is a context in which a group of one or more identifiers might exist. ... A binary tree, a simple type of branching linked data structure. ...


Assembly languages, like most other computer languages, allow comments to be added to assembly source code that are ignored by the assembler. Good use of comments is even more important with assembly code than with higher-level languages, as the meaning of a sequence of instructions is harder to decipher from the code itself. Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ...


Wise use of these facilities can greatly simplify the problems of coding and maintaining low-level code. Raw assembly source code as generated by compilers or disassemblers — code without any comments, meaningful symbols, or data definitions — is quite difficult to read when changes must be made.


Macros

Many assemblers support macros, programmer-defined symbols that stand for some sequence of text lines. This sequence of text lines may include a sequence of instructions, or a sequence of data storage pseudo-ops. Once a macro has been defined using the appropriate pseudo-op, its name may be used in place of an mnemonic. When the assembler processes such a statement, it replaces the statement with the text lines associated with that macro, then processes them just as though they had appeared in the source code file all along (including, in better assemblers, expansion of any macros appearing in the replacement text).


Since macros can have short names but expand to several lines of code, they can be used to make assembly language programs much shorter. They can also be used to add higher levels of structure to assembly programs.


Many assemblers have built-in macros for system calls and other special code sequences.


Macro assemblers often allow macros to take parameters. Some assemblers include quite sophisticated macro languages, incorporating such high-level language elements as optional parameters, symbolic variables, conditionals, string manipulation, and arithmetic operations, all usable during the execution of a given macros, and allowing macros to save context or exchange information. Thus a macro might emit a large number of assembly language instructions or data definitions, based on the macro arguments. This could be used to generate record-style data structures or "unrolled" loops, for example, or could generate entire algorithms based on complex parameters. An organization using assembly language that has been heavily extended using such a macro suite can be considered to be working in a (slightly) higher-level language such programmers are not working with a computer's lowest-level conceptual elements. In computer programming, a parameter is a variable which takes on the meaning of a corresponding argument passed in a call to a subroutine. ...


Macros were used to customize large scale software systems for specific customers in the mainframe era and were also used by customer personnel to satisfy their employers' needs by making specific versions of manufacturer operating systems; this was done, for example, by systems programmers working with IBM's Conversational Monitor System/Virtual Machine (CMS/VM) and with its "real time transaction processing" add-on, Customer Information Control System, CICS.


It was also possible to use solely the macro processing capabilities of an assembler to generate code written in completely different languages, for example, to generate a version of a program in Cobol using a pure macro assembler program containing lines of Cobol code inside assembly time operators instructing the assembler to generate arbitrary code.


This was because, as was realized in the 1970s, the concept of "macro processing" is independent of the concept of "assembly", the former being in modern terms more word processing, text processing, than generating object code. The concept of macro processing in fact appeared in and appears in the C programming language, which supports "preprocessor instructions" to set variables, and make conditional tests on their values. Note that unlike certain previous macro processors inside assemblers, the C preprocessor was not Turing-complete because it lacked the ability to either loop or "go to", the latter allowing the programmer to loop. For the usage of this term in Turing reductions, see Turing complete set. ...


Despite the power of macro processing, it fell into disuse in high level languages while remaining a perennial for assemblers.


This was because many programmers were rather confused by macro parameter substitution and did not disambiguate macro processing from assembly and execution.


Macro parameter substitution is strictly by name: at macro processing time, the value of a parameter is textually substituted for its name. The most famous class of bugs resulting was the use of a parameter that itself was an expression and not a simple name when the macro writer expected a name. In the macro: foo: macro a load a*b the intention was that the caller would provide the name of a variable, and the "global" variable or constant b would be used to multiply "a". If foo is called with the parameter a-c, an unexpected macro expansion occurs.


To avoid this, users of macro processors learned to religiously parenthesize formal parameters inside macro definitions, and callers had to do the same to their "actual" parameters.


PL/I and C feature macros, but this facility was underused or dangerous when used because they can only manipulate text. On the other hand, homoiconic languages, such as Lisp and Prolog, retain the power of assembly language macros because they are able to manipulate their own code as data. “LISP” redirects here. ... Prolog is a logic programming language. ...


Support for structured programming

Some assemblers have incorporated structured programming elements to encode execution flow. The earliest example of this approach was in the Concept-14 macro set developed by Marvin Zloof at IBM's Thomas Watson Research Center, which extended the S/370 macro assembler with IF/ELSE/ENDIF and similar control flow blocks. This was a way to reduce or eliminate the use of GOTO operations in assembly code, one of the main factors causing spaghetti code in assembly language. This approach was widely accepted in the early 80s (the latter days of large-scale assembly language use). Structured programming can be seen as a subset or subdiscipline of procedural programming, one of the major programming paradigms. ... The Thomas J. Watson Research Center is the headquarters for the IBM Research Division. ... GOTO is a statement found in many computer programming languages. ... A plate of spaghetti looks twisted and tangled, which is where the name for spaghetti code comes from. ...


A curious design was A-natural, a "stream-oriented" assembler for 8080/Z80 processors from Whitesmiths Ltd. (developers of the Unix-like Idris Operating System, and what was reported to be the first commercial C compiler). The language was classified as an assembler, because it worked with raw machine elements such as opcodes, registers, and memory references; but it incorporated an expression syntax to indicate execution order. Parentheses and other special symbols, along with block-oriented structured programming constructs, controlled the sequence of the generated instructions. A-natural was built as the object language of a C compiler, rather than for hand-coding, but its logical syntax won some fans. The Zilog Z80 is an 8-bit microprocessor designed and manufactured by Zilog from 1976 onwards. ... Whitesmiths was the first commercial C programming language compiler. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... Idris is an operating system released by Whitesmiths, of Westford, Massachusetts. ... C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ... A diagram of the operation of a typical multi-language, multi-target compiler. ...


There has been little apparent demand for more sophisticated assemblers since the decline of large-scale assembly language development.[citation needed] In spite of that, they are still being developed and applied in cases where resource constraints or peculiarities in the target system's architecture prevent the effective use of higher-level languages.[2]


Use of assembly language

Historical perspective

Historically, a large number of programs have been written entirely in assembly language. Operating systems were almost exclusively written in assembly language until the widespread acceptance of C in the 1970s and early 1980s. Many commercial applications were written in assembly language as well, including a large amount of the IBM mainframe software written by large corporations. COBOL and FORTRAN eventually displaced much of this work, although a number of large organizations retained assembly-language application infrastructures well into the 90s. C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ... COBOL (pronounced //) is a Third-generation programming language, and one of the oldest programming languages still in active use. ... Fortran (previously FORTRAN[1]) is a general-purpose[2], procedural,[3] imperative programming language that is especially suited to numeric computation and scientific computing. ...


Most early microcomputers relied on hand-coded assembly language, including most operating systems and large applications. This was because these systems had severe resource constraints, imposed idiosyncratic memory and display architectures, and provided limited, buggy system services. Perhaps more important was the lack of first-class high-level language compilers suitable for microcomputer use. A psychological factor may have also played a role: the first generation of microcomputer programmers retained a hobbyist, "wires and pliers" attitude.


In a more commercial context, the biggest reasons for using assembly language were size (and hence speed), and reliability: the writers of Cardbox-Plus said simply "we use assembler because then all the bugs are ours". This held true for 8-bit versions of the program, which had no bugs at all, but ironically it turned out to be false with 16 bits: Cardbox-Plus 2.0 had to be upgraded to Cardbox-Plus 2.1 because a bug in Microsoft's macro assembler caused Cardbox-Plus to index the number "-0" differently from the number "0".


Typical examples of large assembly language programs from this time are the MS-DOS operating system, the early IBM PC spreadsheet program Lotus 1-2-3, and almost all popular games for the Atari 800 family of home computers. Even into the 1990s, most console video games were written in assembly, including most games for the Mega Drive/Genesis and the Super Nintendo Entertainment System[citation needed]. The popular arcade game NBA Jam (1993) is another example. On the Commodore 64, Amiga, Atari ST, as well as ZX Spectrum home computers, assembler has long been the primary development language. This was in large part due to the fact that BASIC dialects on these systems offered insufficient execution speed, as well as insufficient facilities to take full advantage of the available hardware on these systems. Some systems, most notably Amiga, even have IDEs with highly advanced debugging and macro facilities, such as the freeware ASM-One assembler, comparable to that of Microsoft Visual Studio facilities (ASM-One predates Microsoft Visual Studio). Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Screenshot of a spreadsheet under OpenOffice A spreadsheet is a rectangular table (or grid) of information, often financial information. ... Lotus 1-2-3 is a spreadsheet program from Lotus Software (now part of IBM). ... Atari built a series of 8-bit home computers based on the MOS Technology 6502 CPU, starting in 1979. ... The Sega Mega Drive ) is a video game console released by Sega in Japan in 1988, North America in 1989, and the PAL region in 1990. ... The Super Nintendo Entertainment System or Super NES (also called SNES and Super Nintendo) was a 16-bit video game console released by Nintendo in North America, Europe, Australasia, and Brazil between 1990 and 1993. ... NBA Jam is a basketball arcade game created by Midway in 1993. ...


The smallest symbolic assembler ever written[citation needed] was The Assembler for the unexpanded VIC-20, written by Don French and published by French Silk. It was only 1639 bytes in length but was packed with features for its size. The Assembler supported the usual symbolic addressing and the definition of character strings and hex strings, but it also allowed address expressions of any number of terms combined with +-*/, logical AND, logical OR, and exponentiation operators. VIC-20 with accessories. ...


Current usage

There have always been debates over the usefulness and performance of assembly language relative to high-level languages, though this gets less attention today. Assembly language has specific niche uses where it is important; see below. But in general, modern optimizing compilers are claimed to render high-level languages into code that can run as fast as hand-written assembly, despite some counter-examples that can be created. The complexity of modern processors makes effective hand-optimization increasingly difficult. Moreover, and to the dismay of efficiency lovers, increasing processor performance has meant that most CPUs sit idle most of the time, with delays caused by predictable bottlenecks such as I/O operations and paging. This has made raw code execution speed a non-issue for most programmers. This article is about computer virtual memory. ...


There are really only a handful of situations where today's expert practitioners would choose assembly language:

  • When a stand-alone binary executable is required, i.e. one that must execute without recourse to the run-time components or libraries associated with a high-level language; this is perhaps the most common situation. These are embedded programs that store only a small amount of memory and the device is intended to do single purpose tasks. Such examples consist of telephones, automobile fuel and ignition systems, air-conditioning control systems, security systems, and sensors.
  • When interacting directly with the hardware
  • When using processor-specific instructions not exploited by or available to the compiler. A common example is the bitwise rotation instruction at the core of many encryption algorithms.
  • When extreme optimization is required, e.g., in an inner loop in a processor-intensive algorithm. Some game programmers are experts at writing code that takes advantage of the capabilities of hardware features in systems enabling the games to run faster.
  • When a system with severe resource constraints (e.g., an embedded system) must be hand-coded to maximize the use of limited resources; but this is becoming less common as processor price/performance improves
  • When no high-level language exists, e.g., on a new or specialized processor
  • Real-time programs that need precise timing and responses, such as simulations, flight navigation systems, and medical equipment. (For example, in a fly-by-wire system, telemetry must be interpreted and acted upon within strict time constraints. Such systems must eliminate sources of unpredictable delays – such as may be created by interpreted languages, automatic garbage collection, paging operations, or preemptive multitasking. Some higher-level languages incorporate run-time components and operating system interfaces that can introduce such delays. Choosing assembly or lower-level languages for such systems gives the programmer greater visibility and control over processing details.)
  • When complete control over the environment is required (for example in extremely high security situations, where nothing can be taken for granted).
  • When writing computer viruses, bootloaders, certain device drivers, or other items very close to the hardware or low-level operating system.
  • When reverse-engineering existing binaries, which may or may not have originally been written in a high-level language.
  • Reverse engineering and modification of video games (known as ROM Hacking), commonly done to games for Nintendo hardware such as the SNES and NES, is possible with a range of techniques, of which the most widely employed is altering the program code at the assembly language level.
  • Assembly language is still used for writing games and other software for graphics calculators. For example, see http://tifreakware.net/tutorials/89/a/calc/fargoii.htm
  • Finally, compiler writers usually write software that generates assembly code, and should therefore be expert assembly language programmers themselves

Nevertheless, assembly language is still taught in most Computer Science and Electronic Engineering programs. Although few programmers today regularly work with assembly language as a tool, the underlying concepts remain very important. Such fundamental topics as binary arithmetic, memory allocation, stack processing, character set encoding, interrupt processing, and compiler design would be hard to study in detail without a grasp of how a computer operates at the hardware level. Since a computer's behavior is fundamentally defined by its instruction set, the logical way to learn such concepts is to study an assembly language. Most modern computers have similar instruction sets. Therefore, studying a single assembly language is sufficient to learn: i) The basic concepts; ii) To recognize situations where the use of assembly language might be appropriate; and iii) To see how efficient executable code can be created from high-level languages.[3] In combinatorial mathematics, a circular shift is a permutation of the entries in a tuple where the last element becomes the first element and all the other elements are shifted, or where the first element becomes the last element and all the other are shifted. ... A router, an example of an embedded system. ... Realtime redirects here. ... A flight control system consists of the flight control surfaces, the respective cockpit controls, connecting linkage, and necessary operating mechanisms to control aircraft in flight The basic fundamentals of aircraft controls has been explained in aeronautics. ... In computer science, garbage collection (GC) is a form of automatic memory management. ... Pre-emptive multitasking is a form of multitasking in which processes are not allowed to take an indefinitely long time to complete execution in the CPU. Each process, in turn, is granted a portion of CPU time (usually called a time slice, on the order of milliseconds). ... A backdoor in a computer system (or cryptosystem or algorithm) is a method of bypassing normal authentication or securing remote access to a computer, while attempting to remain hidden from casual inspection. ... Reverse engineering (RE) is the process of taking something (a device, an electrical component, a software program, etc. ... Computer and video games redirects here. ... Screenshot of Lunar Magic, a level editor for Super Mario World, illustrating how a user can modify the game. ... For the video game system, see Nintendo Entertainment System. ... The Super Nintendo Entertainment System or Super NES (also called SNES and Super Nintendo) was a 16-bit video game console released by Nintendo in North America, Europe, Australasia, and Brazil between 1990 and 1993. ... “NES” redirects here. ... The binary or base-two numeral system is a system for representing numbers in which a radix of two is used; that is, each digit in a binary numeral may have either of two different values. ... It has been suggested that this article or section be merged with Dynamic memory allocation. ... Simple representation of a stack In computer science, a stack is a temporary abstract data type and data structure based on the principle of Last In First Out (LIFO). ... A character encoding is a code that pairs a set of characters (such as an alphabet or syllabary) with a set of something else, such as numbers or electrical pulses. ... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ... A diagram of the operation of a typical multi-language, multi-target compiler. ...


Typical applications

Hard-coded assembly language is typically used in a system's boot ROM (BIOS on IBM-compatible PC systems). This low-level code is used, among other things, to initialize and test the system hardware prior to booting the OS, and is stored in ROM. Once a certain level of hardware initialization has taken place, execution transfers to other code, typically written in higher level languages; but the code running immediately after power is applied is usually written in assembly language. The same is true of most boot loaders. In computing, booting (booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. ... For other uses, see Bios. ... A stylised illustration of a personal computer A personal computer (PC) is a computer whose original sales price, size, and capabilities make it useful for individuals, intended to be operated directly by an end user, with no intervening computer operator. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... In computing, booting is a bootstrapping process that starts operating systems when the user turns on a computer system. ...


Many compilers render high-level languages into assembly first before fully compiling, allowing the assembly code to be viewed for debugging and optimization purposes. Relatively low-level languages, such as C, often provide special syntax to embed assembly language directly in the source code. Programs using such facilities, such as the Linux kernel, can then construct abstractions utilizing different assembly language on each hardware platform. The system's portable code can then utilize these processor-specific components through a uniform interface. C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ... The Linux kernel is a Unix-like operating system kernel. ...


Assembly language is also valuable in reverse engineering, since many programs are distributed only in machine code form, and machine code is usually easy to translate into assembly language and carefully examine in this form, but very difficult to translate into a higher-level language. Tools such as the Interactive Disassembler make extensive use of disassembly for such a purpose. Reverse engineering (RE) is the process of taking something (a device, an electrical component, a software program, etc. ... The Interactive Disassembler, more commonly known as simply IDA, is a commercial disassembler widely used for reverse engineering. ...


A particular niche that makes use of the assembly language is the demoscene. Certain competitions require the contestants to restrict their creations to a very small size (e.g., 1, 4 or 64 KiB), and assembly language is the language of choice to achieve this goal. When resources, particularly CPU-processing constrained systems, like the Amiga and the Commodore 64, are a concern, assembler coding is a must: optimized assembler code is written "by hand" and instructions are sequenced manually by the coder or coders in an attempt to reduce the number of CPU cycles to a minimum; the CPU constraints are so great that every CPU cycle counts. However, using such techniques have enabled systems like the Commodore 64 to produce real-time 3D graphics with advanced effects, a feat which would be considered unlikely or even impossible for a system with a 0.99 MHz processor. The demoscene is a computer art subculture that specializes itself on producing demos, non-interactive audio-visual presentations, which are run real-time on a computer. ...


Related terminology

  • Assembly language or assembler language is commonly called assembly, assembler, ASM, or symbolic machine code. A generation of IBM mainframe programmers called it BAL for Basic Assembly Language.
Note: Calling the language assembler is of course potentially confusing and ambiguous, since this is also the name of the utility program that translates assembly language statements into machine code. Some may regard this as imprecision or error. However, this usage has been common among professionals and in the literature for decades.[4] Similarly, some early computers called their assembler its assembly program.[5])
  • The computational step where an assembler is run, including all macro processing, is known as assembly time.
  • The use of the word assembly dates from the early years of computers (cf. short code, speedcode).
  • A cross assembler (see cross compiler) produces code for one type of processor, but runs on another. This technology is particularly important when developing software for new processors, or when developing for embedded systems. This allows, for instance, a 32-bit x86 processor to assemble code to run on a 64-bit x64 processor.
  • An assembler directive is a command given to an assembler. These directives may do anything from telling the assembler to include other source files, to telling it to allocate memory for constant data.

In computing, the name Short code (singular noun) refers to the language of the same name which was the first actually implemented language[1] used for an electronic computing device. ... Speedcoding or Speedcode was the first higher-order language created for an IBM computer [1]. The language was developed by John Backus in 1953 for the for 701 computer. ... A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is run. ...

Further details

For any given personal computer, mainframe, embedded system, and game console, both past and present, at least one--possibly dozens--of assemblers have been written. For some examples, see the list of assemblers. This is a list of assemblers. ...


On Unix systems, the assembler is traditionally called as, although it is not a single body of code, being typically written anew for each port. A number of Unix variants use GAS. Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... Gas, commanded as as when typed from the shell, is the GNU assembler. ... Gas, commanded as as when typed from the shell, is the GNU assembler. ...


Within processor groups, each assembler has its own dialect. Sometimes, some assemblers can read another assembler's dialect, for example, TASM can read old MASM code, but not the reverse. FASM and NASM have similar syntax, but each support different macros that could make them difficult to translate to each other. The basics are all the same, but the advanced features will differ.[6] The Turbo Assembler (TASM) mainly PC-targeted assembler package was Borlands offering in the x86 assembler programming tool market. ... The Microsoft Macro Assembler (MASM) is a high-level assembler that was produced by Microsoft. ... For the Royal Navy project also known as FASM, see Future Attack Submarine. ... The Netwide Assembler (NASM) is an assembler and disassembler for the Intel x86 architecture. ...


Also, assembly can sometimes be portable across different operating systems on the same type of CPU. Calling conventions between operating systems often differ slightly or not at all, and with care it is possible to gain some portability in assembly language, usually by linking with a C library that does not change between operating systems. CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ...


For example, many things in libc depend on the preprocessor to do OS-specific, C-specific things to the program before compiling. In fact, some functions and symbols are not even guaranteed to exist outside of the preprocessor. Worse, the size and field order of structs, as well as the size of certain typedefs such as off_t, are entirely unavailable in assembly language without help from a configure script, and differ even between versions of Linux, making it impossible to portably call functions in libc other than ones that only take simple integers and pointers as parameters. To address this issue, FASMLIB project provides portable assembly library for Win32 and Linux platforms, but it is yet very incomplete.[7] Libc is a software library for the C computer programming language. ... typedef is a keyword in the C Programming Language. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... This article is about operating systems that use the Linux kernel. ... FASMLIB is a portable general-purpose library for x86 32bit assembly language. ...


Some higher level computer languages, such as C and Borland Pascal, support inline assembly where relatively brief sections of assembly code can be embedded into the high level language code. The Forth programming language commonly contains an assembler used in CODE words. C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ... Turbo Pascal, also known as Borland Pascal, is a cheap and powerful IDE for the DOS environment. ... Inline assembler is a feature of programming languages, that enables very low level code written in assembler to be embedded in a high level language like C. This allows programmers to optimise a very performance-sensitive algorithm by sending individual commands to the computers CPU. This example of inline... Forth is a procedural, stack-oriented, reflective programming language and programming environment. ...


Many people use an emulator to debug assembly-language programs. This article is about emulators in computer science. ...


Example listing of assembly language source code

Address Label Instruction Object code[8]
.begin
.org 2048
a_start .equ 3000
2048 ld length,%
2064 be done 00000010 10000000 00000000 00000110
2068 addcc %r1,-4,%r1 10000010 10000000 01111111 11111100
2072 addcc %r1,%r2,%r4 10001000 10000000 01000000 00000010
2076 ld %r4,%r5 11001010 00000001 00000000 00000000
2080 ba loop 00010000 10111111 11111111 11111011
2084 addcc %r3,%r5,%r3 10000110 10000000 11000000 00000101
2088 done: jmpl %r15+4,%r0 10000001 11000011 11100000 00000100
2092 length: 20 00000000 00000000 00000000 00010100
2096 address: a_start 00000000 00000000 00001011 10111000
.org a_start
3000 a:

Example of a selection of instructions (for a virtual computer[9]) with the corresponding address in memory where each instruction will be placed. These addresses are not static, see memory management. Accompanying each instruction is the generated (by the assembler) object code that coincides with the virtual computer's architecture (or ISA). A Universal Virtual Computer (UVC) is much like a virtual machine (VM) in computing by means that it creates a layer between the underlying computer platform and upperlying software. ... In computer science, a memory address is a unique identifier for a memory location at which a CPU or other device can store a piece of data for later retrieval. ... Memory management is the act of managing computer memory. ... In computer science, object file or object code is an intermediate representation of code generated by a compiler after it processes a source code file. ... An instruction set is (a list of) all instructions, and all their variations, that a processor can execute. ...


See also

The Little Man Computer (LMC) was created by Dr. Stuart Madnick as an instructional model. ... The correct title of this article is . ... Intel Pentium 4 (Northwood version), one example out of a huge number of x86 implementations from Intel, AMD, and others. ... A diagram of the operation of a typical multi-language, multi-target compiler. ... A disassembler is a computer program that translates machine language into assembly language — the inverse operation to that of an assembler. ... This is a list of assemblers. ... An instruction set is (a list of) all instructions, and all their variations, that a processor can execute. ... A microassembler is a type of software used to design the control unit of a computer. ...

References

  1. ^ David Salomon, Assemblers and Loaders. 1993 [1]
  2. ^ NESHLA: The High Level, Open Source, 6502 Assembler for the Nintendo Entertainment System
  3. ^ Hyde, op. cit., Foreword ("Why would anyone learn this stuff?")
  4. ^ Stroustrup, Bjarne, The C++ Programming Language, Addison-Wesley, 1986, ISBN 0-201-12078-X: "C++ was primarily designed so that the author and his friends would not have to program in assembler, C, or various modern high-level languages. [use of the term assembler to mean assembly language]"
  5. ^ Saxon, James, and Plette, William, Programming the IBM 1401, Prentice-Hall, 1962, LoC 62-20615. [use of the term assembly program]
  6. ^ Randall Hyde. Which Assembler is the Best?. Retrieved on 2007-10-19.
  7. ^ "vid". FASMLIB: Features. Retrieved on 2007-10-19.
  8. ^ Murdocca, Miles J.; Vincent P. Heuring (2000). Principles of Computer Architecture. Prentice-Hall. ISBN 0-201-43664-7. 
  9. ^ Principles of Computer Architecture (POCA) – ARCTools virtual computer available for download to execute referenced code, accessed August 24, 2005

Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 292nd day of the year (293rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 292nd day of the year (293rd in leap years) in the Gregorian calendar. ...

Books

  • Computer-Books.us a list of books about Assembly Language available online
  • Dominic Sweetman: See MIPS Run. Morgan Kaufmann Publishers, 1999. ISBN 1-55860-410-3
  • John Waldron: Introduction to RISC Assembly Language Programming. Addison Wesley, 1998. ISBN 0-201-39828-1
  • Jeff Duntemann: Assembly Language Step-by-Step. Wiley, 2000. ISBN 0-471-37523-3
  • Paul Carter: PC Assembly Language. Free ebook, 2001.
    Website
  • Robert Britton: MIPS Assembly Language Programming. Prentice Hall, 2003. ISBN 0-13-142044-5
  • Randall Hyde: The Art of Assembly Language. No Starch Press, 2003. ISBN 1-886411-97-2
    Draft versions available online as PDF and HTML
  • Jonathan Bartlett: Programming from the Ground Up. Bartlett Publishing, 2004. ISBN 0-9752838-4-7
    Available online as PDF and as HTML
  • ASM Community Wiki Book "A Wiki-based book full of helpful ASM info, tutorials and code examples" by the ASM Community

External links

References

Look up assembly language in Wiktionary, the free dictionary.
Wikibooks
Wikibooks has a book on the topic of

Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ... Image File history File links Wikibooks-logo-en. ... Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is a wiki for the creation of books. ... For other uses, see Mainframe. ...

Software

  • MenuetOS - hobby Operating System for the PC written entirely in 64-bit assembly language
  • SB-Assembler for most 8-bit processors/controllers
  • GNU lightning, a library that generates assembly language code at run-time which is useful for Just-In-Time compilers
  • WinAsm Studio, The Assembly IDE - Free Downloads, Source Code, a free Assembly IDE, a lot of open source programs to download and a popular Board
  • nasm, the Netwide Assembler
  • GoAsm - a component of the free "Go" tools: 32-bit and 64-bit Windows programming for x86 and x86-64
MenuetOS (also known as MeOS) is an operating system with a monolithic preemptive, real-time kernel, including video drivers, all written in FASM assembly language, for 64-bit and 32-bit x86 architecture computers, by Ville Mikael Turjanmaa. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... The AMD64 or x86-64 is a 64-bit processor architecture invented by AMD. It is a superset of the x86 architecture, which it natively supports. ... A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. ... Array programming languages (also known as vector or multidimensional languages) generalize operations on scalars to apply transparently to vectors, matrices, and higher dimensional arrays. ... A compiled language is a programming language whose implementations are typically compilers (translators which generate machine code from source code), and not interpreters (step-by-step executors of source code, where no translation takes place). ... Concurrent computing is the concurrent (simultaneous) execution of multiple interacting computational tasks. ... Curly brace or bracket programming languages are those which use balanced brackets ({ and }, also known as brace brackets or simply braces) to make blocks in their syntax or formal grammar, mainly due to being C-influenced. ... A Data-structured language is a programming language in which the data structure is a main organizing principle, representation, model, for data and logic (code) alike, in which both are stored and operated upon, i. ... In computer programming, dataflow programming implements dataflow principles and architecture, and models a program, conceptually if not physically, as a directed graph of the data flowing between operations. ... In computer science, a declarative programming language is a high-level language that describes a problem rather than defining a solution — it makes use of declarative programming. ... A domain-specific programming language (domain-specific language, DSL) is a programming language designed to be useful for a specific set of tasks. ... An esoteric programming language (sometimes shortened to esolang[1]) is a programming language designed as a test of the boundaries of computer programming language design, as a proof of concept, or as a joke. ... Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. ... In computer science, imperative programming, as opposed to declarative programming, is a programming paradigm that describes computation in terms of a program state and statements that change the program state. ... In computer programming, an interpreted language is a programming language whose programs may be executed from source form, by an interpreter. ... Logic programming (which might better be called logical programming by analogy with mathematical programming and linear programming) is, in its broadest sense, the use of mathematical logic for computer programming. ... Machine code or machine language is a system of instructions and data directly executed by a computers central processing unit. ... For other uses, see Macro (disambiguation) A macro in computer science is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure. ... Metaprogramming is the writing of computer programs that write or manipulate other programs (or themselves) as their data or that do part of the work during compile time that is otherwise done at run time. ... This does not cite any references or sources. ... Non-English-based programming languages are computer programming languages that, unlike most well-known programming languages, do not use keywords taken from, or inspired by, the English vocabulary. ... An object-oriented programming language (also called an OO language) is one that allows or encourages, to some degree, object-oriented programming techniques such as encapsulation, inheritance, interfaces, and polymorphism. ... A computer programming language is said to adhere to the off-side rule if in it the scope of declarations (a statement block) is expressed by their indentation, i. ... This article is about the computer programming paradigm. ... Prototype-based programming is a style of object-oriented programming in which classes are not present, and behavior reuse (known as inheritance in class-based languages) is performed via a process of cloning existing objects that serve as prototypes. ... In computer science, reflection is the process by which a computer program of the appropriate type can be modified in the process of being executed, in a manner that depends on abstract features of its code and its runtime behavior. ... A scripting language, script language or extension language, is a programming language that controls software application. ... A synchronous programming language is a programming language optimized for programming reactive systems, systems that are often interrupted and must respond quickly. ... Visual Programming in Mindscript A Visual programming language (VPL) is any programming language that lets users specify programs by manipulating program elements graphically rather than by specifying them textually. ...

  Results from FactBites:
 
Assembly language - Wikipedia, the free encyclopedia (1499 words)
Assembly language, commonly called assembly, asm or symbolic machine code, is a human-readable notation for the machine language that a specific computer architecture uses.
In particular, assembly is often used in writing the low level interaction between the operating system and the hardware, for instance in device drivers.
Assembly language is also valuable in reverse engineering, since many programs are distributed only in machine code form, and machine code is usually easy to translate into assembly language and carefully examine in this form, but very difficult to translate into a higher-level language.
Programming:Assembly - Wikibooks, collection of open-content textbooks (487 words)
Assembly does not provide the abstraction level of such languages; basically it is a one-to-one mapping of the bare machine code instructions to so-called mnemonics.
Unfortunately, assembly language cannot be presented to you as a table of commands and a paragraph of instruction on how these commands are written.
Randall Hyde's High Level Assembly (HLA) is considered a good tool by some for learning assembly language for those who are already skilled in a high-level programming language, such as C or C++.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m