Yuriy Skriga 1: Operating Systems Overview 1 OPERATING SYSTEMS OVERVIEW

- an environment "architecture”
Allows convenient usage; hides the tedious stuff
Allows

efficient usage; parallel activity, avoids wasted cycles
Provides information protection
Gives each user a slice of the resources
Acts as a control program.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Interface
Humans
User Programs
O.S. Interface
O.S.
Hardware Interface/ Privileged Instructions
Disk/Tape/Memory

as simple as running the next process, or it can

use relatively complex rules to pick a running process.

A method for simultaneous CPU execution and IO handling. Processing is going on even as IO is occurring in preparation for future CPU work.

Off Line Processing; not only are IO and CPU happening concurrently, but some off-board processing is occurring with the IO.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Components

This leads to:

Multiprogramming ( dynamic switching ). While one job

waits for a resource, the CPU can find another job to run. It means that several jobs are ready to run and only need the CPU in order to continue.

CPU scheduling is the subject of Chapter 6.

All of this leads to:
memory management
resource scheduling
deadlock protection

which are the subject of the rest of this course.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Components

- Tightly coupled systems that communicate via shared memory.

Used for scientific applications. Used for speed improvement by putting together a number of off-the-shelf processors.





Distributed Systems - Loosely coupled systems that communicate via message passing. Advantages include resource sharing, speed up, reliability, communication.





Real Time Systems - Rapid response time is main characteristic. Used in control of applications where rapid response to a stimulus is essential.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Characteristics

interrupt service routine generally, through the interrupt vector, which contains

the addresses of all the service routines.
Interrupt architecture must save the address of the interrupted instruction.
Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt.
A trap is a software-generated interrupt caused either by an error or a user request.
An operating system is interrupt driven.

make up a typical system.
Any of these devices can cause

an electrical interrupt that grabs the attention of the CPU.

an IO request.
Comparing Synchronous and Asynchronous IO Operations

structures are necessary to keep track of IO in progress.

manages a hierarchy of storage devices in order to make

the best use of resources. In fact, considerable effort goes into this support.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Storage
Hierarchy

Fast and Expensive

Slow an Cheap

hardware, operating system, software)
Information in use copied from slower to

faster storage temporarily
Faster storage (cache) checked first to determine if information is there
If it is, information used directly from the cache (fast)
If not, data copied to cache and used there
Cache smaller than storage being cached
Cache management important design problem
Cache size and replacement policy

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Storage
Hierarchy

malicious or ignorant users.

The User/Supervisor Mode and privileged instructions.

Concurrent threads

might interfere with others. This leads to protection of resources by user/supervisor mode. These resources include:

I/O Define I/O instructions as privileged; they can be executed only in Supervisor mode. System calls get us from user to supervisor mode.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Protection

memory. For instance, it can't modify supervisor code. Depends

on an address translation scheme such as that shown here.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Protection

time. This clock causes an interrupt that causes the operating

system to gain control from a user program.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW

Protection

For machines connected together, this protection must extend across:
Shared resources,
Multiprocessor Architectures,
Clustered Systems
The practice of this is called “distributed operating systems”.

this was the equivalent of a Satellite picture.

The next view

will be at the level of a high flying plane.

After that, we’ll be at ground level, looking at pieces in detail.

1: Operating Systems Overview

OPERATING SYSTEM OVERVIEW