## Operating Systems

An operating system acts as a receptionist, dispatcher, efficiency expert, traffic officer and security guard for your computer.

• It is comprised of a number of managers, such as a hardware manager, network manager etc.
• It effectively allows us to interact with the computer in the way we are used to.

### User Interface Management

The user interface management allows the user to input commands into the computer.

This can be done either by a command line interface or a graphical user interface.

1. It waits for a user to makes a request.
2. It checks if a request is legal based on the user's permissions.
3. It determines which software package will handle the request.
4. It schedules the software to be run on the computer.

### Program Scheduling & Activation

Program scheduling & activation involves the process of running multiple programs on one processor.

• The processor utilization is the percentage of time the processor is busy.
• This process allows the processor utilization to increase as it can run a different process while one is waiting for input.
• The multi-programmed OS allows many programs to be loaded into memory.

If every process has $50\%$ processor utilization, the formula for the processor utilization with $n$ processes is:

$$\text{Processor Utilization}=1-0.5^n$$