Execution (computing)
Each instruction of a program is a description of a particular action which must be carried out, in order for a specific problem to be solved.
This executable is then invoked, most often by an operating system, which loads the program into memory (load time), possibly performs dynamic linking, and then begins execution by moving control to the entry point of the program; all these steps depend on the Application Binary Interface of the operating system.
Most programs execute within multitasking operating system and run-time libraries specific to the source language that provide crucial services not supplied directly by the computer itself.
This supportive environment, for instance, usually decouples a program from direct manipulation of the computer peripherals, providing more general, abstract services instead.
In order for programs and interrupt handlers to work without interference and share the same hardware memory and access to the I/O system, in a multitasking operating system running on a digital system with a single CPU/MCU, it is required to have some sort of software and hardware facilities to keep track of an executing process's data (memory page addresses, registers etc.)
In Linux-based operating systems, a set of data stored in registers is usually saved into a process descriptor in memory to implement switching of context.
Runtime, run time, or execution time is the final phase of a computer program's life cycle, in which the code is being executed on the computer's central processing unit (CPU) as machine code.
More recent advancements in runtime engines enable automated exception handling which provides "root-cause" debug information for every exception of interest and is implemented independent of the source code, by attaching a special software product to the runtime engine.
When treating the runtime system as distinct from the runtime environment (RTE), the first may be defined as a specific part of the application software (IDE) used for programming, a piece of software that provides the programmer a more convenient environment for running programs during their production (testing and similar), while the second (RTE) would be the very instance of an execution model being applied to the developed program which is itself then run in the aforementioned runtime system.
This environment may address a number of issues including the management of application memory, how the program accesses variables, mechanisms for passing parameters between procedures, interfacing with the operating system, and otherwise.
The compiler makes assumptions depending on the specific runtime system to generate correct code.
Virtual machines differ and are organized by their function, shown here: Some virtual machine emulators, such as QEMU and video game console emulators, are designed to also emulate (or "virtually imitate") different system architectures thus allowing execution of software applications and operating systems written for another CPU or architecture.
