A processing method is the way that a particular operating system deals with input.

There are three main types of processing method:

• real-time;
• transaction;
• batch processing.

Real-time processing systems process input data so quickly that the resulting output can affect further input.It is used for applications where it is essential that the computer responds straight away to input.

Examples of applications where real-time processing is used are;

• missile defence systems;
• automatic pilot systems on aircraft;
• monitoring intensive care patients in a hospital.

Transaction, or on-line, processing, is used for applications where input needs to be dealt with straight away but it is not critical if there is a slight delay in the time that it takes for the computer to respond to requests.

Examples of applications where transaction processing is used include the on-line seat booking systems used by airlines and the stock control systems used by catalogue companies like Argos.

A system where transaction processing is used will always give an up-to-the-minute picture of the current situation.

A batch processing system does not respond to input straight away. Instead, input is collected together into a ‘batch’ while the system is off-line.

When a batch is ready to be processed the system goes on-line to carry out the processing of the data.

Batch processing is non-interactive. This means that the user cannot get an immediate response to input as they would with an interactive system.

Examples of applications that use batch processing include producing gas, electricity or water bills and marking OMR sheets from multiple choice examinations.