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Operating systems can have different operational modes. This is the way the computer is used and operated. Some operating systems can use more than one operational mode.

Real-time processing

A real-time operating system (OS) can react fast enough to events in the outside world to control an output. The length of time between the input and the output is called latency.

For example, the engine management system within a car uses a real-time operating system to react to feedback from sensors placed throughout the engine. The OS will then immediately inform the driver if action is to be taken (e.g., oil needs topped up or brake pads need changed). Another example would be a point of sale system in a shop that reacts quickly to sales, warning if stock of any item sold is getting low and reordering it.

Batch processing

In batch processing systems, all data is collected together before being processed in a single operation. Typically the processing of payrolls, electricity bills, invoices and daily transactions are dealt with this way.

This method of operation lends itself to jobs with similar inputs, processing and outputs where no human intervention is needed. Jobs are stored in a queue until the computer is ready to deal with them. Batch processed jobs are often done overnight.

Multiuser processing

Multiuser systems allow several users to have access to computing resources at the same time. Computer game servers will use multiuser systems for online gaming. The CPU will deal with each user in turn.

The CPU allocates a period of time to each user, called time sharing. The processor is so fast that the response time at the most is a fraction of a second and the user feels they are being dealt with immediately.