Software hierarchy

To run, a program must also progress through a series of steps in the software hierarchy.

Executable programs
When you request a program to run, the operating system performs a number of operations to transform the executable program on disk to a running program.
Interrupt handlers
The mechanism for notifying the operating system that an external event has taken place is to interrupt the currently running thread and transfer control to an interrupt handler.
Waiting threads
Whenever an executing program makes a request that cannot be satisfied immediately, such as a synchronous I/O operation (either explicit or as the result of a page fault), that thread is put in a waiting state until the request is complete.
Dispatchable threads
When a thread is dispatchable but not running, it is accomplishing nothing useful. Worse, other threads that are running may cause the thread's cache lines to be reused and real memory pages to be reclaimed, resulting in even more delays when the thread is finally dispatched.
Currently dispatched threads
The scheduler chooses the thread that has the strongest claim to the use of the processor.
Current machine instructions
Most of the machine instructions are capable of executing in a single processor cycle if no TLB or cache miss occurs.

Parent topic: The basics of performance