For slides, lectures and ebook you can browse following link.

http://www.niit.edu.pk/~dr.raihan

Common System Components

Process Management Main Memory ManagementFile ManagementI/O System ManagementSecondary ManagementNetworkingProtection SystemCommand-Interpreter System

System ComponentsOperating System ServicesSystem CallsSystem ProgramsSystem Structure Virtual MachinesSystem Design and ImplementationSystem Generation

Process Management A process is a program in execution. A process needs certain

resources, including CPU time, memory, files, and I/O devices, to accomplish its task.

The operating system is responsible for the following activities in connection with process management. Process creation and deletion. process suspension and resumption. Provision of mechanisms for:

process synchronization process communication Process deadlocks

Main-Memory Management

Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices.

Main memory is a volatile storage device. It loses its contents in the case of system failure/shutdown.

The operating system is responsible for the following activities in connections with memory management: Keep track of which parts of memory are currently being used and by

whom (process). Decide which processes to load when memory space becomes

available. Allocate and deallocate memory space as needed.

File Management

A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.

The operating system is responsible for the following activities in connections with file management: File creation and deletion. Directory creation and deletion. Support of primitives for manipulating files and

directories. Mapping files onto secondary storage. File backup on stable (nonvolatile) storage media.

I/O System Management

OS purpose is to hide complexities of specific hardware device from its user.

The I/O system consists of: A buffer-caching system A general device-driver interface Drivers for specific hardware devices

Every OS need device driver for installation of any specific hardware.

Secondary-Storage Management

Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.

Most modern computer systems use disks as the principle on-line storage medium, for both programs and data.

The operating system is responsible for the following activities in connection with disk management: Free space management Storage allocation Disk scheduling

Networking (Distributed Systems)

A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory.

The processors in the system are connected through a communication network.

Communication takes place using a protocol. TCP/IP, SPX/IPX, etc.

A distributed system provides user access to various system resources.

Access to a shared resource allows: Computation speed-up Increased data availability Enhanced reliability

Protection System

Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources.

The protection mechanism must: distinguish between authorized and

unauthorized usage. specify the controls to be imposed. provide a means of enforcement.

Command-Interpreter System

Primary interface between user and OS. Usually a System Program. Not part of the

kernel. Many commands are given to the operating

system by control statements which deal with: process creation and management I/O handling secondary-storage management main-memory management file-system access protection networking

Command-Interpreter System (Cont.)

The program that reads and interprets control statements is called as

command-line interpreter shell (in UNIX/LINUX)

Its function is to get and execute the next command statement.

Command interpreter can either be Text based or GUI based.

Almost all the OS now support GUI based command interpreter one way or another.

Built in GUI of MS-Windows XX and MacOS or GUI environments for Linux, Unix (Called X-Windows).

Operating System Services Program execution – system capability to load a program into

memory and to run it. I/O operations – since user programs cannot execute I/O operations

directly, the operating system must provide some means to perform I/O.

File-system manipulation – program capability to read, write, create, and delete files.

Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.

Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.

Additional Operating System Functions

Additional functions exist not for helping the user, but rather for ensuring efficient system operations.

• Resource allocation – allocating resources to multiple users or multiple jobs running at the same time.

• Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics.

• Protection – ensuring that all access to system resources is controlled.

System Calls System calls provide the interface between a running program

and the operating system. Generally available as assembly-language instructions. Languages defined to replace assembly language for systems

programming allow system calls to be made directly (e.g., C, C++) In Ms-Windows System Calls are part of Window’s Application

Programmer Interface (API) are available to Compilers (VC++, TC, BC).

Simply, A System Call means how many times a user program (your program in C++, Java) is calling Operating System. In Case of Windows XP how many times your program called the

Windows XP’s built in functions.

System Calls

System Calls run in Privileged mode. Three general methods are used to pass

parameters between a running program and the operating system. Pass parameters in registers. Store the parameters in a table in memory, and the table

address is passed as a parameter in a register. Push (store) the parameters onto the stack by the program,

and pop off the stack by operating system.

Printf function… does it make use of System Calls?Try a simply program and add “Hello World” in While(1) loop. And then look at the

TaskManager (ALT+CTRL+DEL) or download STRACE utility

Windows NT System Calls (Dump from STRACE Utility)

1 133 139 NtOpenKey (0x80000000, {24, 0, 0x40, 0, 0, "\Registry\Machine\Software\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\notepad.exe"}, ... ) == STATUS_OBJECT_NAME_NOT_FOUND

2 133 139 NtCreateEvent (0x100003, 0x0, 1, 0, ... 8, ) == 0x0 3 133 139 NtAllocateVirtualMemory (-1, 1243984, 0, 1244028,

8192, 4, ... ) == 0x0 … 6 133 139 NtOpenDirectoryObject (0x3, {24, 0, 0x40, 0, 0, "\

KnownDlls"}, ... 12, ) == 0x0 7 133 139 NtOpenSymbolicLinkObject (0x1, {24, 12, 0x40, 0,

0, "KnownDllPath"}, ... 16, ) == 0x0 8 133 139 NtQuerySymbolicLinkObject (16, ... "C:\WINNT\

system32", 0x0, ) == 0x0 9 133 139 NtClose (16, ... ) == 0x0

Passing of Parameters As A Table

Types of System Calls

Process controlFile managementDevice managementInformation maintenanceCommunications

MS-DOS Execution

At System Start-up Running a Program

UNIX Running Multiple Programs

Communication Models

Msg Passing Shared Memory

Communication may take place using either message passing or shared memory.

Message Passing Model

Before communication, connection must be opened Both the processes must be programmed in such a way

that they can accept or request a connection Connections are opened using ProcessID’s and HostID’s Calling process requests connection while receiving

process has ability to accept or reject the request. Both the processes usually have two events

Receive_Data and Send_Data. If process A wants to communicate with process B then A Requests for Connection B Accepts the connection A Sends data (its query, question, variable) B receives the data and works on the data and then sends back

the results to A Usually in distributed environment this is the only method

which can be utilized. Socket Programming

Shared Memory Model

Use of Global memory space. Process A and Process B establish one global

space and work on that space. Requires synchronization (difficult to handle) but

very easy to implement. Process A and process B are two threads who want to

share memory A will write to global memory space of the program and B

would read from that memory space. Problem arises when A process was unable to write and B

process reads from that memory space. (Drastic result ) Most programmers favor this method only because of very

easy implementation and requires not programming overloads .

System Programs System programs provide a convenient environment for

program development and execution. The can be divided into: File manipulation Status information File modification Programming language support Program loading and execution Communications Application programs

Most users’ view of the operation system is defined by system programs, not the actual system calls.

System Programs

Most OS supply programs that solve common problems as Web Browsers, Scan Disk etc. Command Interpreter is example of System Program

One method is that command interpreter contains built in function calls such as create file, delete file, Copy file, Change Directory etc.

Another method is that command interpreter can call other system programs.. More flexible.

Unix uses second method and MS uses hybrid method. Copy Command is built in the command interpreter system

but XCopy command is a separate system program.

Operating System Design and Implementation Design Goals

Choice of hardware & Type of system Users goals and System goals

Mechanisms and policies How to & What to Priority of I/O intensive programs over CPU Intensive programs. microkernel

Implementation Linux and Windows in C, DOS in assembly Easier to port OR faster? Increased storage? Better data structure and algorithms or assembly language?

System Design Goals

User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast.

System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient.

Mechanisms and Policies

Mechanisms determine how to do something, policies decide what will be done.

The separation of policy from mechanism is a very important principle, it allows maximum flexibility if policy decisions are to be changed later.

System Implementation

Traditionally written in assembly language, operating systems can now be written in higher-level languages.

Code written in a high-level language: can be written faster. is more compact. is easier to understand and debug.

An operating system is far easier to port (move to some other hardware) if it is written in a high-level language.

Operating System Structure

•Simple Structure

•MS DOS System Structure

•Unix system structure

•Layered Approach

•Microkernels

•Modules

MS-DOS System Structure

MS-DOS – written to provide the most functionality in the least space not divided into modules Single Tasked. Terminate and Stay Resident (TSR) programs

did some sort of multi-programming by hooking interrupts.

Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated.

MS-DOS Layer Structure

UNIX System Structure

UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts. Systems programs The kernel

Consists of everything below the system-call interface and above the physical hardware

Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.

UNIX System Structure

Layered Approach

Modular approach. The operating system is divided into a

number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.

Layered Approach

Debugging is fairly easy as it can be implemented in layers. Each layer only uses its own calls or calls (procedures)

of the layer beneath it. Difficulty is Careful definition of layers, because

each layer can only use layers beneath it. Driver routine for management of hard disk space must

be below the memory management routines because virtual memory needs disk space.

Another problem is that layered approach tends to be a little slow at times because each process has to go through subsequent layers and each layer might add extra calculations or traps.

An Operating System Layer

Microkernel System Structure

Kernels grew in size with increased functionality in the OS. This give birth to the idea of Micro Kernel

Remove unnecessary programs from the kernel into the user space.

Communication takes place between user modules using message passing.

Idea of having Clients and Servers within one system. If a program wants to access a file it does not interact directly with kernel but kernel is just used to pass the messages indirectly.

Microkernels

Benefits:- easier to extend a microkernel- easier to port the operating system to new architectures, As OS main function (kernel) is a small code.- more reliable (less code is running in kernel mode)- more secure (most of the services are running is user mode hence hacking into the service doesn’t provide full access to system kernel)

Operating Systems: Mach OS, Windows NT, Mklinux (Not the linux we know),etc

Monolithic vs Microkernel

What is implemented in kernel space?Monolithic

All OS abstractions (e.g. drivers, file systems, networking, device multiplexing)

Low level, platform independent facilities OS Personality features

Microkernel device drivers, virtual memory and task scheduling

facilities in kernel File systems, networking in user space

Modules

Mach

BSD

Application environment and common services

Solaris Loadable modules

The Mac OS X structure

Memory management

RPC

IPC

Thread Scheduling

Command line interface

File systems

POSIX API

Windows NT Architecture (Simplified View)

In modern operating systems, applications are kept separate from the operating system itself.

The operating system code runs in a privileged processor mode known as kernel-mode and has access to system data and hardware.

Applications run in a non-privileged processor mode known as user mode and have limited access to system data and hardware through a set of tightly controlled application programming interfaces (APIs).

Windows NT (Case Study)

Windows NT is a multithreaded microkernel-based operating system. This is akin to Mach, a multithreaded, microkernel-based UNIX operating system

Keeping the base operating system as small and as tight as possible was one of the primary design goals of Windows NT.

To do this, Microsoft kept in the base operating system only those functions that could not reasonably be performed elsewhere.

Functionality pushed out of the kernel was put in six non-privileged servers known as protected subsystems.

The protected subsystems provide the traditional operating system support to applications through a feature-rich set of APIs. Note: With Windows NT version 4.0, the GUI system was put “back” into

the kernel for display performance considerations. (This also caused some robustness problems)

Windows NT (Case Study)

This design results in a very stable base operating system. Enhancements occur at the protected subsystem level.

New protected subsystems can be added without modifying either the base operating system or the other existing protected subsystems

Windows NT (Environment Subsystems)

Win32 2000 uses the Win32 subsystem as the main operating

environment; Win32 is used to start all processes. It also provides all the keyboard, mouse and graphical display capabilities.

MS-DOS MS-Dos environment is provided by a Win32 application

called the virtual dos machine (VDM), a user-mode process that is paged and dispatched like any other 2000 thread.

OS/2 subsystems runs OS/2 applications. IBM and MS were developing OS/2 together when BILL

GATES had a brilliant idea, People call Bill Gates a big cheat because of this idea but nonetheless it was brilliant for the Computer industry.

Windows NT (Environment Subsystems)

16-Bit Windows Environment: Provided by a VDM that incorporates Windows on

Windows. Provides the Windows 3.1 kernel routines and sub

routines for window manager and GDI functions. The POSIX subsystem

Is designed to run POSIX applications following the POSIX.1 standard which is based on the UNIX model.

Logon and Security Subsystems Authenticates users logging to Windows 2000 systems.

Users are required to have account names and passwords.

The authentication package authenticates users whenever they attempt to access an object in the system.

Virtual Machines

A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware.

A virtual machine provides an interface identical to the underlying bare hardware.

The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory.

Virtual Machines (Cont.)

The resources of the physical computer are shared to create the virtual machines. Each process is provided with a virtual copy of

the underlying computer. Minidisks Virtual-machine software runs in kernel mode Virtual user mode, virtual kernel mode –--

(physical user mode) Share minidisk

System Models

Non-virtual Machine Virtual Machine

Advantages/Disadvantages of Virtual Machines

The virtual-machine concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines. This isolation, however, permits no direct sharing of resources.

A virtual-machine system is a perfect vehicle for operating-systems research and development. System development is done on the virtual machine, instead of on a physical machine and so does not disrupt normal system operation.

The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate to the underlying machine.

Java Virtual Machine

Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM).

JVM consists of

- class loader

- class verifier

- runtime interpreter

VMware

Guest and host operating system Good for testing Virtualization layer

CPU memory I/O deviceshardware

Host operating system (Linux)

Virtualization Layer

application application application application

Guest operating system

Guest operating system

Guest operating system

Java Virtual Machine

ClassBytecodeJvm – class loader & Java interpreterJVM in hardware --Java chip

Java Virtual Machine

What is DotNet Architecture?

System Generation (SYSGEN)

Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site.

SYSGEN program obtains information concerning the specific configuration of the hardware system.

Booting – starting a computer by loading the kernel. Bootstrap program – code stored in ROM that is

able to locate the kernel, load it into memory, and start its execution.

System Boot (Cont) Bootstrap locates the kernel and loads it into main

memory, and starts its execution. Bootstrap loader fetches a more complex boot program

from disk, which in turn loads the kernel. Bootstrap is in the form of read-only memory Instruction register is loaded with a predefined memory

location and execution starts there. Some system store the OS in firmware and copy it to

RAM for fast execution. Bootstrap loader in firmware, OS on disk –boot block

(block zero) ---windows, Mac OS X, Unix Boot disk – system disk Bootstrap traverse the file system and finds the OS kernel