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.
The advantage of using DMA is that the DMAC performs the data transfer. The CPU is not tied up for the entire duration of the transfer; however it must still program the DMAC. In general DMA is faster than programmed I/O and therefore useful for large data transfers. IRQ stands for interrupt request. Interrupts are used to perform automatic serial polling and to implement asynchronous (background) data transfers.