A flat fee, also referred to as a flat rate or a linear rate, refers to a pricing structure that charges a single fixed fee for a service, regardless of usage.[1] Less commonly, the term may refer to a rate that does not vary with usage or time of use.
Synchronous: interrupt occurs as a result of current process, otherwise asynchronous. User requested: interrupt occurs because of direct result by user task, otherwise coerced. Maskable: if desired the interrupt can be disabled by a user task, otherwise unmasked.
An interrupt is a signal (an interrupt request) generated by some event external to the CPU, which causes the CPU to stop what it is doing (stop executing the code it is currently running) and jump to a separate piece of code designed by the programmer to deal with the event which generated the interrupt request.