OPERATING SYSTEMSOPERATING SYSTEMS

• Goals of the course• Definitions of operating systems• Operating system goals• What is not an operating system• Computer architecture• O/S services

• Goals of the course• Definitions of operating systems• Operating system goals• What is not an operating system• Computer architecture• O/S services

This lecture will cover:This lecture will cover:

This Lecture will also cover:This Lecture will also cover:

• O/S resource management• O/S achievement history• Hardware architecture• Processes• Interrupts

• O/S resource management• O/S achievement history• Hardware architecture• Processes• Interrupts

Goals of the CourseGoals of the Course

This course is to provide a combined applied/ theoretical background in Operating Systems and Systems Programming to improve students’ understanding:

1. Systems software design

2. Systems programming

3. Performance analysis

4. Performance tuning

This course is to provide a combined applied/ theoretical background in Operating Systems and Systems Programming to improve students’ understanding:

1. Systems software design

2. Systems programming

3. Performance analysis

4. Performance tuning

Some PrerequisitesSome Prerequisites

The Study of Operating Systems Relies on Many Areas:

1. Mathematics

(a) Discrete Mathematics

(b) Basic Calculus

(c)Probability (Exponential Distribution, Poisson

Processes)

The Study of Operating Systems Relies on Many Areas:

1. Mathematics

(a) Discrete Mathematics

(b) Basic Calculus

(c)Probability (Exponential Distribution, Poisson

Processes)

2. Computer Science

(a) Computer Architecture

(b) Programming Language Design

(c) Software Design

(d) Data Structures/ Algorithms

Don’t Panic if you are not familiar

with all the topics, but it is best to be

exposed to most of them.

2. Computer Science

(a) Computer Architecture

(b) Programming Language Design

(c) Software Design

(d) Data Structures/ Algorithms

Don’t Panic if you are not familiar

with all the topics, but it is best to be

exposed to most of them.

Other PrerequisitesOther Prerequisites

Operating System DefinitionsOperating System Definitions

Operating System - a program that acts as an intermediary between a user of a computer and the computer hardware.

Resource Allocator - manages and allocates resources.

Control Program - controls the execution of user programs and operation of I/O devices.

Kernel - the one program running at all times (all else being application programs).

Operating System - a program that acts as an intermediary between a user of a computer and the computer hardware.

Resource Allocator - manages and allocates resources.

Control Program - controls the execution of user programs and operation of I/O devices.

Kernel - the one program running at all times (all else being application programs).

O/S Design GoalsO/S Design Goals

An Operating System (O/S for short) provides the following:

1. A run time programming interface for applications.

2. Resource management.

An Operating System (O/S for short) provides the following:

1. A run time programming interface for applications.

2. Resource management.

O/S Design goals include:1. Convenience - Reduce Complexity for programmers/ users.

2. Efficiency - Allow “efficient” access to system resources.

3. Flexibility - Adding new features should be easy.

O/S Design goals include:1. Convenience - Reduce Complexity for programmers/ users.

2. Efficiency - Allow “efficient” access to system resources.

3. Flexibility - Adding new features should be easy.

What is not an O/SWhat is not an O/S

1. Programming Language Compilers - Translators

2. Interpreter - Shell/ User Interface

3. Library - A set of commands/ utilities

These features are typically provided

as part of the O/S but are strictly

speaking not the O/S.

1. Programming Language Compilers - Translators

2. Interpreter - Shell/ User Interface

3. Library - A set of commands/ utilities

These features are typically provided

as part of the O/S but are strictly

speaking not the O/S.

Computer ArchitectureComputer Architecture

The following layers of abstraction are used (from highest to lowest):

1. Applications Software - Custom programs to support users.

2. Systems Software - Controls the hardware.

3. Hardware - The physical control

of the system (signals).

The following layers of abstraction are used (from highest to lowest):

1. Applications Software - Custom programs to support users.

2. Systems Software - Controls the hardware.

3. Hardware - The physical control

of the system (signals).

Web Browser Games

Data Base WordProcessor

Compiler Shell Editor

Operating System

Physical Network

Machine Language

Micro CodePhysical Devices

Application Software

Systems Software

Hardware

Figure 1: Computer Systems ArchitectureFigure 1: Computer Systems Architecture

O/S ServicesO/S Services

Some O/S services for users are:

1. Program execution - Read program into memory/

run it return control when done.

2. Peripheral Access - I/O device driver interface.

3. Persistent Object Management-

File system structure.

4. Security - File System, Network.

Some O/S services for users are:

1. Program execution - Read program into memory/

run it return control when done.

2. Peripheral Access - I/O device driver interface.

3. Persistent Object Management-

File system structure.

4. Security - File System, Network.

5. Error Detection/ Handling - Hardware failure, program errors.

6. Program Creation Tools - Debugging/ text editing etc.

7. Accounting - Billing for computer access

5. Error Detection/ Handling - Hardware failure, program errors.

6. Program Creation Tools - Debugging/ text editing etc.

7. Accounting - Billing for computer access

Other O/S ServicesOther O/S Services

O/S Resource ManagementO/S Resource Management

O/S controls are intrusive because they both consume the resources which they seek to control and mediate conflicting requests.

O/S controls are intrusive because they both consume the resources which they seek to control and mediate conflicting requests.

Resource AttributesResource Attributes

Resources have properties governing their use including:

1. Preemption - How expensive is it for the device/ resource?

2. Renewability - Does the resource get replenished?

3. Scheduling - Does order of allocation matter?

4. Persistence - Does it’s lifetime extend beyond that of the process which creates it?

5. Sharing - Is it suited to be accessed by many users?

Resources have properties governing their use including:

1. Preemption - How expensive is it for the device/ resource?

2. Renewability - Does the resource get replenished?

3. Scheduling - Does order of allocation matter?

4. Persistence - Does it’s lifetime extend beyond that of the process which creates it?

5. Sharing - Is it suited to be accessed by many users?

Scheduling/ Allocation PolicyScheduling/ Allocation Policy

The scheduled allocation of resources reflects policies including:

1. Fairness

2. Starvation Freedom

3. Maximum Throughput

4. Maximum Utilization

5. Minimize Response time.

The scheduled allocation of resources reflects policies including:

1. Fairness

2. Starvation Freedom

3. Maximum Throughput

4. Maximum Utilization

5. Minimize Response time.

O/S AchievementsO/S Achievements

Denning's list of conceptual breakthroughs (1980):

Processes --- A program in executionMemory Management Information protection and securityScheduling and resource managementSystem Structure

Denning's list of conceptual breakthroughs (1980):

Processes --- A program in executionMemory Management Information protection and securityScheduling and resource managementSystem Structure

A Traditional Hardware ArchitectureA Traditional Hardware Architecture

The traditional von Neumann structure consists of: 1) Processor - Also called the CPU (Central Processing Unit) our example has the registers:

PC --- Program Counter IR --- Instruction Register MAR --- Memory Address Register MBR --- Memory Buffer Register I/O AR --- I/O Address Register I/O BR --- I/O Buffer Register

The traditional von Neumann structure consists of: 1) Processor - Also called the CPU (Central Processing Unit) our example has the registers:

PC --- Program Counter IR --- Instruction Register MAR --- Memory Address Register MBR --- Memory Buffer Register I/O AR --- I/O Address Register I/O BR --- I/O Buffer Register

2) Memory --- (Volatile)

3) Peripherals --- I/O Devices

4) Systems Interconnection --- Links the Other Components (Bus)

2) Memory --- (Volatile)

3) Peripherals --- I/O Devices

4) Systems Interconnection --- Links the Other Components (Bus)

A Traditional Hardware Architecture (Continued)

A Traditional Hardware Architecture (Continued)

Figure 2:

von Neumann Architecture

Figure 2:

von Neumann Architecture

The register structure comes from Stallings; the names mean:

1) PC --- Program Counter --- Address of next instruction 2) IR --- Instruction Register --- Current OpCode to execute 3) MAR --- Memory Address Register --- Memory Pointer 4) MBR --- Memory Buffer Register --- Buffer for memory access 5) I/O AR --- I/O Address Register --- I/O Pointer 6) I/O BR --- I/O Buffer Register --- Buffer for I/O access User registers are not shown here.

The register structure comes from Stallings; the names mean:

1) PC --- Program Counter --- Address of next instruction 2) IR --- Instruction Register --- Current OpCode to execute 3) MAR --- Memory Address Register --- Memory Pointer 4) MBR --- Memory Buffer Register --- Buffer for memory access 5) I/O AR --- I/O Address Register --- I/O Pointer 6) I/O BR --- I/O Buffer Register --- Buffer for I/O access User registers are not shown here.

Process ContextProcess Context

The context of a process consists of:

1) The Current Instruction Pointer (the IP)2) Register Contents3) Memory used by that process

This is the machine's current state used to determine the machines next state when running a particular program.

The context of a process consists of:

1) The Current Instruction Pointer (the IP)2) Register Contents3) Memory used by that process

This is the machine's current state used to determine the machines next state when running a particular program.

The Model of ExecutionThe Model of Execution

Traditionally called the fetch/ execute cycle, in its simplest form: (figure 3)

Traditionally called the fetch/ execute cycle, in its simplest form: (figure 3)

Time- Sharing Systems- Interactive Computing

•The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).

•A job is swapped in and out of memory to the disk.

•On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” not from a card reader, but rather from the user’s keyboard.

•On line file system must be available for users to access data and code.

Time- Sharing Systems- Interactive Computing

•The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).

•A job is swapped in and out of memory to the disk.

•On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” not from a card reader, but rather from the user’s keyboard.

•On line file system must be available for users to access data and code.

Motivation for Interrupts

An interrupt is an external asynchronous event changing the flow of control of a process (my definition). It is also refers to triggering such an event.

14.1 - The Problem

Peripherals tend to have slow response time (especially if waiting on human supplied input).

Motivation for Interrupts

An interrupt is an external asynchronous event changing the flow of control of a process (my definition). It is also refers to triggering such an event.

14.1 - The Problem

Peripherals tend to have slow response time (especially if waiting on human supplied input).

The Solution

To improve CPU utilization we want to allow the CPU to continue to execute while awaiting I/O as seen in Figure.When an interrupt is detected an interrupt handling routine is typically invoked. There are times (such as interrupt processing) where it may be desirable to disallow further interrupts.

The Solution

To improve CPU utilization we want to allow the CPU to continue to execute while awaiting I/O as seen in Figure.When an interrupt is detected an interrupt handling routine is typically invoked. There are times (such as interrupt processing) where it may be desirable to disallow further interrupts.

Interrupting the Fetch/Execute CycleInterrupting the Fetch/Execute Cycle

The fetch/ execute cycle is adjusted to support interrupts.(figure 4)

The fetch/ execute cycle is adjusted to support interrupts.(figure 4)

Interrupt Processing

Processing an interrupt on most architectures involves the following steps:1. Finish the current instruction2. Push the IP on the stack3. Set the IP to the interrupt handler's address.4. Preserve the process context (i.e. push registers).5. Executing the interrupt handling routine.6. Restore the process context (i.e. pop registers).7. Pop the IP from the stack

Interrupt Processing

Processing an interrupt on most architectures involves the following steps:1. Finish the current instruction2. Push the IP on the stack3. Set the IP to the interrupt handler's address.4. Preserve the process context (i.e. push registers).5. Executing the interrupt handling routine.6. Restore the process context (i.e. pop registers).7. Pop the IP from the stack