Introduction Of I / O

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In computing, input/output, or I/O, refers to 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 or data received by the system, and outputs are the signals or data sent from it.
The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation.
I/O devices are used by a person (or other system) to communicate with a computer.
a keyboard or a mouse may be an input device for a computer, while monitor send printers are considered output devices for a computer.
Devices for communication between computers, such as modems and network cards, typically serve for both input and output.

Goals for I/O

• Users should access all devices in a uniform manner.
• Devices should be named in a uniform manner.
• The OS, without the intervention of the user program, should handle recoverable errors.
• The OS must maintain security of the devices.
• The OS should optimize the performance of the I/O system.

Input and output operation in operating system:-

In computer architecture, the combination of the CPU and main memory (i.e. memory that the CPU can read and write to directly, with individual instructions) is considered the brain of a computer, and from that point of view any transfer of information from or to that combination.
for example :to or from a disk drive, is considered I/O.
The CPU and its supporting circuitry provide memory-mapped I/O that is used in low-level computer programming in the implementation of device drivers.
An I/O algorithm is one designed to exploit locality and perform efficiently when data reside on secondary storage, such as a disk drive.

Input/output memory-mapped in o/s:-

The CPU and its supporting circuitry provide memory-mapped I/O that is used in low-level computer programming in the implementation of device drivers. An I/O algorithm is one designed to exploit locality and perform efficiently when data reside on secondary storage, such as a disk drive.

Input/output port-mapped in o/s:-

Port-mapped I/O usually requires the use of instructions which are specifically designed to perform I/O operations.

Interaction b/w user and i/o:-

The output from these devices is input for the computer.
Similarly, printers and monitors take as input signals that a computer outputs. They then convert these signals into representations that human users can see or read.
For a human user the process of reading or seeing these representations is receiving input.
These interactions between computers and humans is studied in a field called human–computer interaction.

i/o procedure:-

A user process requesting I/O makes a call in the form:-DOIO(stream, mode, amount, destination, semaphores) .
Where DOIO is the name of the relevant I/O procedure

stream:- is the ident no. of the stream on which I/O is to take place

mode:- operation required,- input, output, scan, etc,- may indicate char code too

amount: how much data to be transferred.

destination (source): memory area where data is to be transferred to/from

semaphore: address of semaphore 'request serviced' to be signaled by the device handler when I/O operation is complete.