Function of Operating SystemsIntroduction

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

IO Functions• input-output control system

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)

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

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

Memory Management - Loader

What happens if you load programs in a different order?

The ‘Loader’ remembers.

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.

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.