Porting
Encyclopedia
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.g. different CPU
, operating system
, or third party library
). The term is also used when software/hardware is changed to make them usable in different environments.
Software is portable
when the cost of porting it to a new platform is less than the cost of writing it from scratch. The lower the cost of porting software, relative to its implementation cost, the more portable it is said to be.
or architecture
, the code must be "carried" to the new system.
The term is not generally applied to the process of adapting software to run with less memory on the same CPU and operating system, nor is it applied to the rewriting of source code in a different language
(i.e. language conversion or translation).
Software developers often claim that the software they write is portable, meaning that little effort is needed to adapt it to a new environment. The amount of effort actually needed depends on several factors, including the extent to which the original environment (the source platform) differs from the new environment (the target platform), the experience of the original authors in knowing which programming language
constructs and third party library calls are unlikely to be portable, and the amount of effort invested by the original authors in only using portable constructs (platform specific constructs often provide a cheaper solution).
means that most desktop software is never ported to a different CPU. In that same market, the choice of operating systems has effectively been reduced to three: Microsoft Windows
, Mac OS
/Mac OS X, and Unix
/Linux
. However, in the embedded systems market, portability remains a significant issue.
International standards, such as those promulgated by the ISO
, greatly facilitate porting by specifying details of the computing environment in a way that helps reduce differences between different standards-conforming platforms
. Writing software that stays within the bounds specified by these standards represents a practical although nontrivial effort. Porting such a program between two standards-compliant platforms (such as POSIX.1
) can be just a matter of loading the source code and recompiling it on the new platform. However, practitioners often find that various minor corrections are required, due to subtle platform differences. Most standards suffer from "gray areas" where differences in interpretation of standards lead to small variations from platform to platform.
There also exists an ever-increasing number of tools to facilitate porting, such as the GNU Compiler Collection
, which provides consistent programming languages on different platforms, and Autotools, which automates the detection of minor variations in the environment and adapts the software accordingly before compilation.
The compilers for some high-level programming languages (e.g. Eiffel
, Esterel
) gain portability by outputting source code in another high level intermediate language
(such as C
) for which compilers for many platforms are generally available.
Two activities related to (but distinct from) porting are emulating
and cross-compiling.
, modern compilers translate to a machine independent intermediate code in order to enhance portability of the compiler and minimize design efforts.
The intermediate language defines a virtual machine that can execute all programs written in the intermediate language (a machine is defined by its language and vice versa). The intermediate code instructions are translated into equivalent machine code sequences by a code generator to create executable code. It is also possible to skip the generation of machine code by actually implementing the virtual machine in machine code. This virtual machine implementation is called an interpreter, because it reads in the intermediate code instructions one by one and after each read executes the equivalent machine code sequences (the interpretation) of the read intermediate instruction directly.
The use of intermediate code enhances portability of the compiler, because only the machine dependent code (the interpreter or the code generator) of the compiler itself needs to be ported to the target machine. The remainder of the compiler can be imported as intermediate code and then further processed by the ported code generator or interpreter, thus producing the compiler software or directly executing the intermediate code on the interpreter.
The machine independent part can be developed and tested on another machine (the host machine). This greatly reduces design efforts, because the machine independent part needs to be developed only once to create portable intermediate code.
An interpreter is less complex and therefore easier to port than a code generator, because it is not able to do code optimizations due to its limited view of the program code (it only sees one instruction at a time and you need a sequence to do optimization). Some interpreters are extremely easy to port, because they only make very minimal assumptions about the instruction set of the underlying hardware. As a result the virtual machine is even simpler than the target CPU.
Writing the compiler sources entirely in the programming language the compiler is supposed to translate, makes the following approach, better known as compiler bootstrapping
, feasible on the target machine:
The difficult part of coding the optimization routines is done using the high-level language instead of the assembly language of the target.
According to the designers of the BCPL
language, interpreted code (in the BCPL case) is more compact than machine code; typically by a factor of two to one. Interpreted code however runs about ten times slower than compiled code on the same machine.
The designers of the Java programming language
try to take advantage of the compactness of interpreted code, because in Java a program needs to be transmitted over the Internet before execution can start on the target's Java Virtual Machine
.
or a video game console
, is converted to run on a different platform. Earlier video game "ports" were often not true ports, but rather reworked versions of the games. However, more and more video games are now being developed using software that can output code for PCs as well as for one or more consoles without the need for actual porting. Many early ports suffered significant gameplay quality issues because the hardware of PCs and consoles differed so dramatically.
Arcade perfect is a term used to describe video games which have been ported from an arcade
version to another platform, such as a console, without any alterations to the game's workings. This means that graphics, sound and gameplay
, along with the game's other characteristics, are identical to the arcade version.
"Console Port" is a term specifically used to describe a game that was originally made for a console (such as PS3 or Xbox 360) before an identical version is created which can be played on a personal computer
. This term has been widely used by the gaming community, primarily in a negative way due to the higher levels of performance that computers had during that generation of gaming being underutilized, partially due to console hardware being fixed throughout their run (with games being developed with these specs in mind,) while PCs become more powerful as hardware evolves, but also due to ported games sometimes being poorly optimized for PCs, or lazily ported.
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, porting is the process of adapting software so that an executable program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
can be created for a computing environment that is different from the one for which it was originally designed (e.g. different CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
, or third party library
Library (computer science)
In computer science, a library is a collection of resources used to develop software. These may include pre-written code and subroutines, classes, values or type specifications....
). The term is also used when software/hardware is changed to make them usable in different environments.
Software is portable
Software portability
Portability in high-level computer programming is the usability of the same software in different environments. The prerequirement for portability is the generalized abstraction between the application logic and system interfaces...
when the cost of porting it to a new platform is less than the cost of writing it from scratch. The lower the cost of porting software, relative to its implementation cost, the more portable it is said to be.
Etymology
The term "port" is derived from the Latin portare, meaning "to carry". When code is not compatible with a particular operating systemOperating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
or architecture
Computer architecture
In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....
, the code must be "carried" to the new system.
The term is not generally applied to the process of adapting software to run with less memory on the same CPU and operating system, nor is it applied to the rewriting of source code in a different language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
(i.e. language conversion or translation).
Software developers often claim that the software they write is portable, meaning that little effort is needed to adapt it to a new environment. The amount of effort actually needed depends on several factors, including the extent to which the original environment (the source platform) differs from the new environment (the target platform), the experience of the original authors in knowing which programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
constructs and third party library calls are unlikely to be portable, and the amount of effort invested by the original authors in only using portable constructs (platform specific constructs often provide a cheaper solution).
History
The number of significantly different CPUs and operating systems used on the desktop today is much smaller than in the past. The dominance of the x86 architectureInstruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
means that most desktop software is never ported to a different CPU. In that same market, the choice of operating systems has effectively been reduced to three: Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, Mac OS
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
/Mac OS X, and Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
/Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
. However, in the embedded systems market, portability remains a significant issue.
International standards, such as those promulgated by the ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
, greatly facilitate porting by specifying details of the computing environment in a way that helps reduce differences between different standards-conforming platforms
Platform (computing)
A computing platform includes some sort of hardware architecture and a software framework , where the combination allows software, particularly application software, to run...
. Writing software that stays within the bounds specified by these standards represents a practical although nontrivial effort. Porting such a program between two standards-compliant platforms (such as POSIX.1
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
) can be just a matter of loading the source code and recompiling it on the new platform. However, practitioners often find that various minor corrections are required, due to subtle platform differences. Most standards suffer from "gray areas" where differences in interpretation of standards lead to small variations from platform to platform.
There also exists an ever-increasing number of tools to facilitate porting, such as the GNU Compiler Collection
GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
, which provides consistent programming languages on different platforms, and Autotools, which automates the detection of minor variations in the environment and adapts the software accordingly before compilation.
The compilers for some high-level programming languages (e.g. Eiffel
Eiffel (programming language)
Eiffel is an ISO-standardized, object-oriented programming language designed by Bertrand Meyer and Eiffel Software. The design of the language is closely connected with the Eiffel programming method...
, Esterel
Esterel
Esterel is a synchronous programming language for the development of complex reactive systems. The imperative programming style of Esterel allows the simple expression of parallelism and preemption...
) gain portability by outputting source code in another high level intermediate language
Intermediate language
In computer science, an intermediate language is the language of an abstract machine designed to aid in the analysis of computer programs. The term comes from their use in compilers, where a compiler first translates the source code of a program into a form more suitable for code-improving...
(such as C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
) for which compilers for many platforms are generally available.
Two activities related to (but distinct from) porting are emulating
Emulator
In computing, an emulator is hardware or software or both that duplicates the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system...
and cross-compiling.
Porting compilers
Instead of translating directly into machine codeMachine code
Machine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...
, modern compilers translate to a machine independent intermediate code in order to enhance portability of the compiler and minimize design efforts.
The intermediate language defines a virtual machine that can execute all programs written in the intermediate language (a machine is defined by its language and vice versa). The intermediate code instructions are translated into equivalent machine code sequences by a code generator to create executable code. It is also possible to skip the generation of machine code by actually implementing the virtual machine in machine code. This virtual machine implementation is called an interpreter, because it reads in the intermediate code instructions one by one and after each read executes the equivalent machine code sequences (the interpretation) of the read intermediate instruction directly.
The use of intermediate code enhances portability of the compiler, because only the machine dependent code (the interpreter or the code generator) of the compiler itself needs to be ported to the target machine. The remainder of the compiler can be imported as intermediate code and then further processed by the ported code generator or interpreter, thus producing the compiler software or directly executing the intermediate code on the interpreter.
The machine independent part can be developed and tested on another machine (the host machine). This greatly reduces design efforts, because the machine independent part needs to be developed only once to create portable intermediate code.
An interpreter is less complex and therefore easier to port than a code generator, because it is not able to do code optimizations due to its limited view of the program code (it only sees one instruction at a time and you need a sequence to do optimization). Some interpreters are extremely easy to port, because they only make very minimal assumptions about the instruction set of the underlying hardware. As a result the virtual machine is even simpler than the target CPU.
Writing the compiler sources entirely in the programming language the compiler is supposed to translate, makes the following approach, better known as compiler bootstrapping
Bootstrapping (compilers)
In computer science, bootstrapping is the process of writing a compiler in the target programming language which it is intended to compile...
, feasible on the target machine:
- Port the interpreter. This needs to be coded in assembly code, using an already present assemblerAssemblerAssembler may refer to:* Assembler , for an assembly language, a computer program to translate between lower-level representations of computer programs...
on the target. - Adapt the source of the code generator to the new machine.
- Execute the adapted source using the interpreter with the code generator source as input. This will generate the machine code for the code generator.
The difficult part of coding the optimization routines is done using the high-level language instead of the assembly language of the target.
According to the designers of the BCPL
BCPL
BCPL is a procedural, imperative, and structured computer programming language designed by Martin Richards of the University of Cambridge in 1966.- Design :...
language, interpreted code (in the BCPL case) is more compact than machine code; typically by a factor of two to one. Interpreted code however runs about ten times slower than compiled code on the same machine.
The designers of the Java programming language
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
try to take advantage of the compactness of interpreted code, because in Java a program needs to be transmitted over the Internet before execution can start on the target's Java Virtual Machine
Java Virtual Machine
A Java virtual machine is a virtual machine capable of executing Java bytecode. It is the code execution component of the Java software platform. Sun Microsystems stated that there are over 4.5 billion JVM-enabled devices.-Overview:...
.
Porting in gaming
Porting is also the term used when a computer game designed to run on one platform, be it a personal computerPersonal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
or a video game console
Video game console
A video game console is an interactive entertainment computer or customized computer system that produces a video display signal which can be used with a display device to display a video game...
, is converted to run on a different platform. Earlier video game "ports" were often not true ports, but rather reworked versions of the games. However, more and more video games are now being developed using software that can output code for PCs as well as for one or more consoles without the need for actual porting. Many early ports suffered significant gameplay quality issues because the hardware of PCs and consoles differed so dramatically.
Arcade perfect is a term used to describe video games which have been ported from an arcade
Arcade game
An arcade game is a coin-operated entertainment machine, usually installed in public businesses such as restaurants, bars, and amusement arcades. Most arcade games are video games, pinball machines, electro-mechanical games, redemption games, and merchandisers...
version to another platform, such as a console, without any alterations to the game's workings. This means that graphics, sound and gameplay
Gameplay
Gameplay is the specific way in which players interact with a game, and in particular with video games. Gameplay is the pattern defined through the game rules, connection between player and the game, challenges and overcoming them, plot and player's connection with it...
, along with the game's other characteristics, are identical to the arcade version.
"Console Port" is a term specifically used to describe a game that was originally made for a console (such as PS3 or Xbox 360) before an identical version is created which can be played on a personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
. This term has been widely used by the gaming community, primarily in a negative way due to the higher levels of performance that computers had during that generation of gaming being underutilized, partially due to console hardware being fixed throughout their run (with games being developed with these specs in mind,) while PCs become more powerful as hardware evolves, but also due to ported games sometimes being poorly optimized for PCs, or lazily ported.
See also
- Software portabilitySoftware portabilityPortability in high-level computer programming is the usability of the same software in different environments. The prerequirement for portability is the generalized abstraction between the application logic and system interfaces...
- Language bindingLanguage bindingIn computing, a binding from a programming language to a library or OS service is an API providing that service in the language.Many software libraries are written in systems programming languages such as C or C++...
- Console emulator
- List of system quality attributes
- Source portSource portA source port is a software project based on the source code of a computer game's engine that allows the game to be played on operating systems or computing platforms with which the game was not originally compatible. Source ports are created by fans after the original developer hands over the...
- Write once, compile anywhereWrite once, compile anywhereWrite once, compile anywhere refers to writing software that compiles, and is thus usable, on all platforms. As opposed to Sun's write once, run anywhere slogan, cross-platform compatibility is implemented at the source code level, rather than at the compiled binary code level.There are many...
- PoshlibPoshlibPosh is a software framework used in cross-platform software development. It was created by Brian Hook. It's BSD licensed and currently at version 1.3.002.The Posh software framework provides a header file and an optional C source file....
- Cross-platformCross-platformIn computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...