"Write once, run anywhere" (WORA), or sometimes write once, run everywhere (WORE), is a slogan created by Sun Microsystems

Sun Microsystems

Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...

 to illustrate the cross-platform

Cross-platform

In 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...

 benefits of the Java 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...

. Ideally, this means Java can be developed on any device, compiled into a standard bytecode

Bytecode

Bytecode, also known as p-code , is a term which has been used to denote various forms of instruction sets designed for efficient execution by a software interpreter as well as being suitable for further compilation into machine code...

 and be expected to run on any device equipped with a 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:...

 (JVM). The installation of a JVM or Java interpreter on chips, devices or software packages has become an industry standard practice.

This means a programmer can develop code on a PC and can expect it to run on Java enabled cell phones, as well as on routers and mainframe

Mainframe computer

Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...

s equipped with Java, without any adjustments. This is intended to save software developers the effort of writing a different version of their software for each platform

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...

 or 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...

 they intend to deploy on.

This idea originated as early as in the late 1970s, when the UCSD Pascal

UCSD Pascal

UCSD Pascal was a Pascal programming language system that ran on the UCSD p-System, a portable, highly machine-independent operating system. UCSD Pascal was first released in 1978...

 system was developed to produce and interpret p-code

P-Code machine

In computer programming, a p-code machine, or portable code machine is a virtual machine designed to execute p-code...

. UCSD Pascal (along with the Smalltalk virtual machine) was a key influence on the design of the 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:...

, as is cited by James Gosling

James Gosling

James A. Gosling, OC is a computer scientist, best known as the father of the Java programming language.-Education and career:In 1977, Gosling received a B.Sc in Computer Science from the University of Calgary...

.

The catch is that since there are multiple JVM

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:...

 implementations, on top of a wide variety of different operating systems such as 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...

, 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...

, Solaris, NetWare, HP-UX

HP-UX

HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...

, and 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...

, there can be subtle differences in how a program may execute on each JVM/OS combination, which may require an application to be tested on various target platforms. This has given rise to the joke among Java developers, "Write Once, Debug Everywhere".

See also

• Criticisms of cross-platform development and this slogan
• Write once, compile anywhere
  Write once, compile anywhere
  Write 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...
  
  
  • Free Pascal
    Free Pascal
    Free Pascal Compiler is a free Pascal and Object Pascal compiler.In addition to its own Object Pascal dialect, Free Pascal supports, to varying degrees, the dialects of several other compilers, including those of Turbo Pascal, Delphi, and some historical Macintosh compilers...
    
    
• C to Java Virtual Machine compilers
• Parrot virtual machine
  Parrot virtual machine
  Parrot is a register-based process virtual machine designed to run dynamic languages efficiently. It uses just-in-time compilation for speed to reduce the interpretation overhead. It is currently possible to compile Parrot assembly language and PIR to Parrot bytecode and execute it...