1.2 Operating System Structure

1. Monolithic System

• The earliest and most common OS architecture.

• Every component of OS contained in the kernel and can directly communicate with any other (i.e by using function call).

• The kernel typically executes with unrestricted access to the computer system (refer next diagram)

1. Monolithic System

User Space

Kernel Space

Application

System Call Interface

MM PS IPC FS

I/O Net

Kernel

. . .

MM- Memory management

PS- Process scheduler

IPC- Interprocess communictaion

FS- File System

I/O- Input Output manager

Net- Network manager

2. Layered System

• To overcome the issue of monolithic architecture by grouping components that performs similar functions into layers

• Each layer communicates with those above and below it.

• Lower-level layers provide services to higher-level layer using interfaces that hide their implementation

• Layer OS are more modular than monolithic OS because the implementation of each layer can be modified without requiring any modification to other layers

2. Layered System

• Each component hides how it performs its job and presents a standard interface that other components can use to request its services

• In a layer approach, a user process’s request may need to pass through many layers before it is services

• Early example of layer OS is THE (Technische Hogeschool Eindhoven)• Many of today’s OS including Windows XP and Linux

implement some level of layering.• Main advantage is simplicity of construction and

debugging.

2. Layered System

User spaceKernel space

User applications

I/O Management

Operator – process communication

Memory management

Processor allocation and

multiprogramming

Layer 4

Layer 3

Layer 2

Layer 1

Layer 0

user

Hardw

are

Layers of THE Operating System• The OS is divided into a number of layers (levels)

• The bottom layer (layer 0), is the hardware.• The highest (layer N) is the user interface.

3. Virtual Machines OS

• Virtual Machine OS is to support concurrent execution of different operating system on a computer .

• The resources of the physical computer are shared to create the virtual machines.– CPU scheduling can create the appearance that users

have their own processor.– Spooling and a file system can provide virtual card

readers and virtual line printers.– A normal user time-sharing terminal serves as the

virtual machine operator’s console.

3. Virtual Machines OS

Non-virtual Machine Virtual Machine

3. Advantages & Disadvantages of Virtual Machine OS

• Advantages:– provides complete protection of system resources. Each

virtual machine is isolated from all other virtual machines.

– perfect vehicle for operating-systems RND.– System development is done on the virtual machine,

instead of on a physical machine. So does not disrupt normal system operation.

• Disadvantages:– This isolation permits no direct sharing of resources.– Difficult to implement due to the effort required to

provide an exact duplicate to the underlying machine.

4. Client-Server Model

• Is one of the extended machine

Network Operating System (NOS)

• NOS is the system software of a local area network (LAN) that integrates the network's hardware components, usually adequate for connecting up to 50 workstations.

• Included such features as a menu-driven administration interface, tape backup of file-server software, security restrictions, facilities for sharing printers, central storage of application programs and databases, remote log-in via modem, and support for discuss workstations.

• A network operating system establishes and maintains the connection between the workstations and the file server; the physical connections alone aren't sufficient to support networking.

Network Operating System (NOS)

• 2 type of NOS :– Peer to pear – Client Server

• Example of NOS operating system– Microsoft Windows (Workgroups)– Microsoft Windows NT Server

Open Source vs Closed Source OS

Open Source Closed Source

User can get the source code Source code - is held by the developer

Allow user can modify and change it, following the guidelines in the accompanying license

Only developer can make any changes or study on it

Example : Ubuntu , RedHat Windows NT, Windows Vista,

Owner : LINUX Microsoft the owner and developer of Windows

Terminologies in OS

• Cooperative multitasking• Preemptive multitasking• Multithreading

Terminologies in OS : Cooperative Multitasking

• A type of multitasking in which the process currently controlling the CPU must offer control to other processes. It is called cooperative because all programs must cooperate for it to work

Terminologies in OS : Preemptive Multitasking

Terminologies in OS : Multithreading

Three Major Component of Operating System

• Process Management• File Management• Memory Management

Process Management

File Management

Memory Management