Programmed input–output: Difference between revisions

Revision as of 13:08, 6 April 2022

Revision as of 05:30, 14 August 2022

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{{Short description|Method of CPU communication with peripheral devices}}

{{Refimprove|date=June 2013}}

'''Programmed input–output''' (also '''programmable input/output''', '''programmed input/output''', '''programmed I/O''', '''PIO''') is a method of [[data transmission]], via [[input/output]] (I/O), between a [[central processing unit]] (CPU) and a [[peripheral]] device, such as a [[network adapter]] or a [[Parallel ATA]] storage device. Each data item transfer is initiated by an instruction in the program, involving the CPU for every transaction. In contrast, in [[direct memory access]] (DMA) operations, the CPU is uninvolved in the data transfer.

The term can refer to either [[memory-mapped I/O]] (MMIO) or port-mapped I/O (PMIO). PMIO refers to transfers using a special [[address space]] outside of normal memory, usually accessed with dedicated instructions, such as <samp>IN</samp> and <samp>OUT</samp> in [[x86]] architectures. MMIO<ref>{{cite book |last=Stallings |first=William |date=2012 |title=Computer Organization and Architecture |edition=9th |publisher=Pearson}}</ref> refers to transfers to I/O devices that are mapped into the normal address space available to the program. PMIO was very useful for early microprocessors with small address spaces, since the valuable resource was not consumed by the I/O devices.

The best known example of a PC device that uses programmed I/O is the Parallel AT Attachment (ATAPATA) interface and Serial ATA interface; however, the AT Attachment interface can also be operated in any of several DMA modes. Many older devices in a PC also use PIO, including legacy serial ports, legacy parallel ports when not in ECP mode, keyboard and mouse [[PS/2 port]]s, legacy Musical Instrument Digital Interface ([[MIDI]]) and [[joystick]] ports, the interval timer, and older network interfaces.

== PIO mode in the ATA interface ==