Operating Systems: Role, Functions, and Types, Slides of Introduction to Computing

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CS101 Introduction to Computing

Lecture 11

Operating Systems

Focus of the last lecture: computer SW

1. We found out about the role SW plays in a computing environment
2. We learned to distinguish between SW belonging to the system & application categories
3. Also discussed the different types of SW licenses:
   1. Proprietary
   2. Free
   3. Open source
   4. Shareware
   5. Trialware

Why Have OSes?

1. User/programmer convenience
2. Greater resource utilization

The Role of An OS

• The 1st program that runs when a typical computer is turned ON, and the last one to finish running when the computer is turned OFF
• It manages the HW and SW resources of the computer system, often invisibly. These include the processor, memory, disk drives, etc.
• It provides a simple, consistent way for applications to interact with the HW without having to know all the details of the HW

Are OS’es Essential?

• No. If a computer has been designed for limited functionality (e.g. it runs just a single program all the time as in a automatic clothes washing machine), it does not require a traditional OS
• In limited-functionality computers, an OS just adds to the overhead unnecessarily, which impedes the computer’s performance
• In these situations, the required parts of the OS are integrated into the the only program that is going to run

In the beginning …

• A single user ran a single program ran on a single computer
  • there was no need for an OS
• Then came computer operators who ran multiple programs for multiple users one after the other – still, no need for an OS
• Later computers became powerful, & became able to run multiple programs, simultaneously. That’s when the need for OS’es arose for: - Managing the resources of the computers efficiently - Making use of computers convenient for users/programmers

Processor Management

• Various programs compete for the attention of the uP for their own purposes
• The OS plays the role of the honest referee, making sure that each app gets the necessary attention required for its proper execution
• It tries to optimally manages the limited processing capacity of the uP to the greatest good of all the users & apps

Memory Management

• Straight forward for a single-user, single tasking
• Each app must have enough private memory in which to execute
• App can neither run into the private memory space of another app, nor be run into by another app
• Different types of memory (e.g. main, cache) in the system must be used properly, so that each app can run most effectively

Device Management

• Applications talk to devices through the OS and OS talks to and manages devices through Device Drivers
• Example: When we print to a laser printer, we do not need to know its details. All we do is to tell the printer device driver about what needs to be printed and it takes care of the details

Application Interface

• App developers do not need to know much about the HW, especially the uP, while they are developing their app
• The OS provides all apps with a straight-forward and consistent interface to the HW
• Example: An app uses the OS to store data on the disk drive. For that, the app does not need to know about the exact physical characteristics of that drive; it just tells the OS to do that through the app interface, and the OS takes cares of all the details of the task

OS Components

Kernel

Command Interpreter (Shell)

File Manager

Device Manager

GUI

Loader

Types of OS’es

Classification w.r.t. the type of computers they run on and the type of applications they support

• Real-Time Operating System (RTOS)
• Single-User, Single Task
• Single-User, Multi-Tasking
• Multi-User

RTOS (1)

• Used to run computers embedded in machinery, robots, scientific instruments and industrial systems
• Typically, it has little user interaction capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use
• Examples: Wind River, QNX, Real-time Linux, Real- time Windows NT