Multithreading refers to the ability of an operating system to support multiple threads of execution within a single process. The traditional approach of a single thread of execution per process, in which the concept of a thread is not recognized, is referred to as a single-threaded approach. In a multithreaded environment, a process is defined as the unit of resource allocation and a unit of protection. The following are associated with processes:

• A virtual address space that holds the process image
• Protected access to processors, other processes (for interprocess communication), files, and I/O resources (devices and channels)

Within a process, there may be one or more threads, each with the following:

• A thread execution state (Running, Ready, etc.).
• A saved thread context when not running; one way to view a thread is as an independent program counter operating within a process.
• An execution stack.
• Some per-thread static storage for local variables.
• Access to the memory and resources of its process, shared with all other threads in that process.

While the process is running, processor registers are controlled by that process, and the contents of these registers are saved when the process is not running. In a multithreaded environment, there is still a single process control block and user address space associated with the process, but now there are separate stacks for each thread, as well as a separate control block for each thread containing register values, priority, and other thread-related state information.

Discuss (the benefits of threads) if an application should be implemented as a set of related units of execution, it is far more efficient to do so as a collection of threads rather than a collection of separate processes.