Programmed input–output (also programmable input/output, programmed input/output, programmed I/O, PIO) is a method of

data transmission Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point o ...

, via

input/output In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals ...

(I/O), between a

central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...

(CPU) and a

peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...

device, such as a

Parallel ATA Parallel ATA (PATA), originally , also known as IDE, is a standard interface designed for IBM PC-compatible computers. It was first developed by Western Digital and Compaq in 1986 for compatible hard drives and CD or DVD drives. The connection ...

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 Direct memory access (DMA) is a feature of computer systems and allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU). Without DMA, when the CPU is using programmed input/output, it is t ...

(DMA) operations, the CPU is uninvolved in the data transfer. The term can refer to either

memory-mapped I/O Memory-mapped I/O (MMIO) and port-mapped I/O (PMIO) are two complementary methods of performing input/output (I/O) between the central processing unit (CPU) and peripheral devices in a computer. An alternative approach is using dedicated I/O pro ...

(MMIO) or port-mapped I/O (PMIO). PMIO refers to transfers using a special

address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve st ...

outside of normal memory, usually accessed with dedicated instructions, such as IN and OUT in

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...

architectures. MMIO 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 (PATA) 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 The PS/2 port is a 6-pin mini-DIN connector used for connecting keyboards and mice to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987. The PS/2 mo ...

s, legacy

MIDI MIDI (; Musical Instrument Digital Interface) is a technical standard that describes a communications protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, and re ...

and

joystick A joystick, sometimes called a flight stick, is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. A joystick, also known as the control column, is the principal cont ...

ports, the interval timer, and older network interfaces.

PIO mode in the ATA interface

The PIO interface is grouped into different modes that correspond to different

transfer rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

s. The

electrical signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

ing among the different modes is similar — only the cycle time between transactions is reduced in order to achieve a higher transfer rate. All ATA devices support the slowest mode — Mode 0. By accessing the information registers (using Mode 0) on an ATA drive, the CPU is able to determine the maximum transfer rate for the device and configure the ATA controller for optimal performance. The PIO modes require a great deal of CPU overhead to configure a data transaction and transfer the data. Because of this inefficiency, the DMA (and eventually Ultra Direct Memory Access (

UDMA Udma is a census town in Kasaragod district in the Indian States and territories of India, state of Kerala. Demographics As of 2011 India census, Udma census town had population of 8,115 which constitutes 3,593 males and 4,522 females. Udma c ...

) interface was created to increase performance. The simple digital logic needed to implement a PIO transfer still makes this transfer method useful today, especially if high transfer rates are unneeded as in

embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...

s, or with

field-programmable gate array A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware d ...

(FPGA) chips, where PIO mode can be used with no significant performance loss. Two additional advanced timing modes have been defined in the

CompactFlash CompactFlash (CF) is a flash memory mass storage device used mainly in portable electronic devices. The format was specified and the devices were first manufactured by SanDisk in 1994. CompactFlash became one of the most successful of the e ...

specification 2.0. Those are PIO modes 5 and 6. They are specific to CompactFlash.

PIO Mode 5

A PIO Mode 5 was proposed with operation at 22 MB/s, but was never implemented on hard disks because CPUs of the time would have been crippled waiting for the hard disk at the proposed PIO 5 timings, and the DMA standard ultimately obviated it. While no

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

was ever manufactured to support this mode, some

motherboard A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...

manufacturers preemptively provided

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

support for it. PIO Mode 5 can be used with CompactFlash cards connected to ATA via CF-to-ATA adapters.

References

{{DEFAULTSORT:Programmed input output Input/output

PIO mode in the ATA interface

PIO Mode 5

See also

References