Computing - Operating Systems

Hide the complexities of the hardware from the user.

On the hard drive.

On the ROM.

Read only memory.

The bios.

A layer of software that allows one computer to simulate another and to run more than one operating system.

_ _ A _ _ pplication _ _ P _ _ rogramming _ _ I _ _ nterface

To hide the true complexities of an operation to the end user.

• An API is like a waiter in a restaurant
• You look at the menu and give the waiter (i.e. the API) your request
• The waiter takes the request to the kitchen (i.e. the OS)
• The kitchen sends back the prepared dish via the waiter

Handling resource management.

• Processor scheduling
• Backing store management
• Memory management
• I/O devices

Where the OS controls what instructions are sent to the processor.

Allows programs to run simultaneously, since multiple instructions are queued.

Any non-volatile data storage that will hold a computer’s data.

Allows the reading and writing of files. Keeping track of free space.

Where the OS allocates each process some memory.

On the RAM.

The OS allocated virtual memory on the hard drive instead.

• Round robin - each process uses the processor in turn
• Shortest job next
• Priority system/queue

Where the OS communicates with I/O devices and handles drivers.

Where the OS deals with software and hardware interrupts.

A signal from a hardware device or program that causes the operating system to stop processing its current instructions and switch priority.

1. Current processor state is saved
2. Source of the interrupt is identified
3. Appropriate interrupt service routine called
4. Processor state is restored

When the keys are pressed.

When the mouse is moved.