EMBEDDED SYSTEMS DESIGN- UNIT IV�TOPIC 1: OPERATING SYSTEM BASICS

BY

PRIYANKA YADLAPALLI

Operating System Basics

Operating System

Bridge between the application s/w and system resources

Manages

the resources

Processes

Time

File System

I/O System

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Fig.: Operating system architecture

Fig.: Operating system architecture

Operating System Basics

The Kernel

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The core of the OS

• Manages the system resources
• Communication among the system services
• Acts as the abstraction layer between system resource and user applications
• Contains system libraries and services

Operating System Basics

The Kernel contain different services for handling the following

• Process management
• Setting up the memory space
• Loading the process code into memory space
• Allocating system resources
• Scheduling and executing
• Setting up and managing Process Control Block (PCB)
• Inter Process Communication, and synchronisation
• Process termination/deletion

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Primary Memory Management

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• The Memory Management Unit (MMU) of the kernel
• Keeps track of which part of memory being used by which process

is responsible for dynamic memory allocation

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Operating System Basics

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• File System Management service of kernel is responsible for

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• Creation, deletion, and modification of files, and directories
• Saving of files in secondary storage memory
• Automatic allocation of file space based on available free space
• Naming convention
• File system management operations are OS dependent.

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Operating System Basics

I/O System(Device) Management

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• Maintains a list of all the I/O devices
• Routes the I/O requests from user applications to appropriate I/O devices
• Provides Application Programming Interfaces (APIs)
• Updates the list of available devices dynamically when a new device is installed.
• Interacts with an I/O devices through a set of system calls which are implemented in a service called Device Driver.

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• The Device Drivers are specific to the devices or class of devices.

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• The service ‘Device Manager’ is responsible for
• handling all I/O device related operations
• Loading and unloading of device drivers
• Exchanging information and control signals to and from the device.

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Operating System Basics

Secondary Storage Management

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The secondary storage management service of the kernel deals with

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• Disk storage allocation
• Disk scheduling
• Free Disk space management

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Protection Systems

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This service of the kernel

• Implement security policies in multiuser supported OS one user can access other user’s data without authority
• Some of the system resources can be restricted for some users

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Operating System Basics

Kernel Space and User Space

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Kernel Space

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• A contiguous memory area (OS dependent) of primary memory where kernel code is kept.
• Protected from unauthorised access by user program/applications

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User Space

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• Memory space where user programs are loaded and executed.

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• Some Operating Systems do not segregate the kernel space and user space.

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• Most of the operating systems keep the kernel in main memory and it is not swapped out into the secondary memory

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Operating System Basics

Monolithic Kernel and Microkernel

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Monolithic Kernel

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• All kernel services run in the kernel space
• All kernel modules run within the same memory space under a single thread.

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Major drawback

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• Any error/failure in any of the modules leads to the crashing of the entire kernel.

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Examples: Linux, Solaris, MS-DOS

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Micro Kernel

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• Incorporates only the essential set of services
• Other services are implemented in the programs called as servers run in user space
• Highly modular design

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Examples: Mach, QNX, Minix 3

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Advantages

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• Robustness: if an error occur in any of the services running as server, then that service (server) can be reconfigured, and re-started without re-starting the whole OS.

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• Configurability: any service runs as server application can be modified without restarting the entire OS. This makes the system dynamically configurable.

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