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The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch-execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
The three-state process management model is designed to overcome this problem, by introducing a new state called the BLOCKED state. This state describes any process which is waiting for an I/O event to take place. In this case, an I/O event can mean the use of some device or a signal from another process. The three states in this model are:
An execution model covers things such as what is an indivisible unit of work, and what are the constraints on the order in which those units of work may take place. For example, the addition operation is an indivisible unit of work in many languages, and in sequential languages such units of work are constrained to take place one after the other.
A sample UML class and sequence diagram for the Command design pattern. [3]In the above UML class diagram, the Invoker class doesn't implement a request directly. Instead, Invoker refers to the Command interface to perform a request (command.execute()), which makes the Invoker independent of how the request is performed.
Process groups are identified by a positive integer, the process group ID, which is the process identifier of the process that is (or was) the process group leader. Process groups need not necessarily have leaders, although they always begin with one. Sessions are identified by the process group ID of the session leader.
Depending on the OS, a process may be made up of multiple threads of execution that execute instructions concurrently. [1] [2] While a computer program is a passive collection of instructions typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may ...
The child process has an exact copy of all the memory segments of the parent process. In modern UNIX variants that follow the virtual memory model from SunOS-4.0, copy-on-write semantics are implemented and the physical memory need not be actually copied.
The base of each is exec (execute), followed by one or more letters: e – An array of pointers to environment variables is explicitly passed to the new process image. l – Command-line arguments are passed individually (a list) to the function. p – Uses the PATH environment variable to find the file named in the file argument to be executed.