Operating Systems

Definition

An operating system is a collection of programs that manage the resources of the system, and provides a interface between the user, the hardware, and the applications.

Types of Operating Systems

Simple device control embedded on a ROM chip

Complex Windows NT Unix, Etc.

Complex Operating Systems

Consist of multiple programs

The Kernel is the core of the operating systems.

Kernel

The kernel is responsible for:

Device control Memory management Scheduling Inter-process communication Processing of interrupts and exceptions.

Single vs. Multiple Processor

Single Processor can only run one instruction at a time.

It gives the appearance of multi-tasking with switching.

2 Types of Switching

Co-Operative Switching

Pre-Emptive Switching

Co-Operative Switching

In co-operative switching the task which is currently running must voluntarily give up the processor for the next process to run.

Problem with Co-Operative Switching

If first process “hangs up” and does not give up control the computer freezes. No other task can run.

Pre-Emptive Switching

In pre-emptive switching the task that is currently running is forced to give up control after a certain period of time. If a task “hangs” it does not stop subsequent task from running.

Pre-Emptive Switching is“Better” than Co-Operative Switching

16-Bit vs. 32-bit

32-bit programs use pre-emptive switching.

16-bit program use co-operative switching and are more susceptible to “freezing”.

Context Switching

The process of switching from one task to another is called “Context Switching”.

Scheduling

Scheduling is the process of deciding which task should run next.

Time Slice

The amount of time that a process runs before giving up control is called time slice or quantum period.

Co-Operative Processing

In co-operative processing the processes are generally arranged such that as the top process is completed each task moves up one place.

Pre-Emptive Scheduling Pre-emptive scheduling uses a real-

time clock, which generates interrupts at regular intervals. Each time an interrupt occurs the processor is switched to another task.

Generally tasked are assigned a priority in pre-emptive scheduling.

Multiprocessor vs. Multiprocessing

A multi-processor computer is a computer with more than one processor.

Categories of Multi-Processor Computers

Shared memory multi-processor

Distributed memory multi-processor

Shared Memory Multi-processor

Shared memory multi-processors have multiply CPUs, and they all share the same memory.

Communication between the processors is easy to implement, but care must be taken to synchronize memory access.

Distributed Memory Multi-Processors Also has multiple CPUs, but each

CPU has its own memory. In distributed memory multi-

processor memory synchronization is not a problem,

but communication between the processors is often slow and complicated.

Related to Multi-Processors

Networked Systems

Distributed Systems

Networked Systems

Networked systems consist of multiple computers, networked together. Users are aware of the different computers that make up the system.

Distributed Systems

Distributed systems also consist of multiple computer but unlike the networked system the various computers are transparent to the user.

Operating System A computer is a set of resources for

the movement, storage, and processing of data.

The operating system is responsible for managing these resources scheduling the other programs and providing the user interface.