1. Function of Operating Systems
Introduction

2. The Operating System MUST:
provide and manage hardware resources
provide an interface between the user and the machine
provide an interface between applications software and the machine
provide security for the data on the system
provide utility software to allow maintenance to be done

3. IO Functions
input-output control system

4. Evolution Now higher level languages are developed, the OS needs:
A translator program with:
Assembler (translates assembly language)
Compiler (translates high level language)
Interpreter (translates then runs 1 line at a time)

5. Memory Management - Scheduling
The OS must manage the CPU time so that the user has no concept of tasks being dealt with individually.

6. Memory Management - Spooling
The I/O phase should not hold up the CPU which can easily happen when mechanical operations cannot keep up. Eg??

7. Memory Management - Loader
What happens if you load programs in a different order? The ‘Loader’ remembers.

8. Memory Management - Users
What happens if two users want to use the same program at the same time? Programs such as this compiler, working in the way described, are called re-entrant.

9. KEY TERMS
Memory Management - The process of the operating system being able to control the use of the computer’s memory, rather than the user doing it
Scheduling - When there is more than one thing which could be done at a time something has to decide what will be done first.
Spooling - store all input and output on a high-speed device such as a disk until the slower peripheral device is ready.