3-4-1 The Role of the Operating System

• To provide an interface to hide the complexities of the hardware from the user.
• Manages hardware and communication resources.

Hardware resources managed by the OS:

• Processors
• Storage
• Input/Output Devices
• Data

Allocating Processor Time:

Several programs can be running on a computer at the same time sharing one processor.
A running program is cann a process.
One of the jobs of the operationg system is to share the processor time between the processes.

Multi-tasking/Multi-programming:
These are the same thing.
Mulit-tasking is when a number of programs are running at the same time, sharing the time of the processor e.g. using a word processor while listening to music.

Time Slice:The processor time rotates between active processes until they have finished.
This is handled by the Processor Schedular Program. The complexities are hidden from the user and application programs.

Memory Management:The Memory Management Program (part of the OS) allocates spacein the main memory (RAM) for program instructions and data while programs are running.

Storing Data onto Secondary Storage (Disk):

Fragmentation: is the splitting up of the execution of a program in order to run more quickly.

A file will be stored in clusters spread throughout a disk. The complexity of keeping track of where the file is stored is hidden from the user.

Operating System:
e.g. Print a word processing document.

The operating system does all the communication with the printer for us.

• The OS sends a block of data to the printer, then the next block and so on.


this continues until the document is finished. The complexity of this is hidden from the user.