Input and output
With input / output (abbreviated to I / O ; English input / output , short I / O ) refers to - as a term from the computer or the computer science - the communication / interaction of an information system with its 'outside world', z. B. its users or other information systems, and actions to read and write data . Inputs are signals (z. B. command line ) or data which the system receives , from the system outputs are sent .
What the 'outside world' is depends on how you look at it: From the point of view of the computer as the executing processor , B. also the programs 'inputs'. In a program (this is generally the object of consideration), application data from / for user (s) or other system (s) are the most important inputs or outputs; for subroutines it is u. a. also the call and return values ( parameters ) of corresponding programs / parts, for a printer it is the texts / graphics etc. to be printed, including the associated control commands.
Basics
Inputs and outputs are the interfaces to their 'outside world' for programs running on a computer . They make it possible to use programs or program parts (such as subroutines ) for individual and different purposes / situations.
For interaction between user and program are external peripheral devices available, via the operating system (. Eg the system bus and / or device drivers are operated and controlled) and mechanical or other electronic communication links. This is necessary because there are many different protocols and the devices can differ in terms of word length and processing speed.
In the methodology for software development , a distinction is made in connection with inputs and outputs according to whether data flows from outside (e.g. from users) to the system (or vice versa) or whether it is data that is stored or read in the system , changed or deleted ( create, read, update, delete = CRUD ).
hardware
The processor addresses the external devices via I / O controllers (less powerful but cheaper) or I / O processors (very powerful but more expensive). These serve as an abstraction layer and from the CPU with simple READ-( READ ) and write ( WRITE control commands). The devices themselves are connected directly via data, control and address buses. They contain buffers to temporarily store requests and responses.
Programmed input / output , interrupt-driven I / O and DMA are available to carry out this communication .
For users , the input devices are usually keyboard , mouse and joystick , output devices are usually monitors , printers or portable storage media such as CDs , etc.
In relation to the environment, the input can also mean sensors (for temperature, speed, pressure ...). The output would then be e.g. B. Power controllers, valve controls, etc. Something like this is used in the field of control and measurement technology.
software
In the software area, one can distinguish between input in the command line, input within the program from keyboard, mouse or joystick query, read access to a storage medium or direct read access to an A / D converter or the like.
The software output does not generally run via the command line, but exclusively in the program as write access to the screen, printer, memory or an A / D converter or similar.