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21CA1205

Operating Systems

Session 2

Operating System Functionalities

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Operating Systems Functions

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Operating Systems Functions

Memory Management
Processor Management
File Management
Device Management
I/O Management
Secondary storage Management
Security …
Command Interpretation
Networking
Communication Management
Job Accounting

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Process Management

A process is a program in execution. It is a unit of work within the system.
Program is a passive entity, while process is an active entity.
Process needs resources to accomplish its task

CPU, memory, I/O, files, etc.
Initialization of data

Process termination requires reclaim of any reusable resources
A thread is a basic unit of CPU utilization within a process.

Single-threaded process. Instructions are executed sequentially, one at a time, until completion
Process has one program counter specifying location of next instruction to execute

Multi-threaded process has one program counter per thread

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Process Management Activities

Creating and deleting processes
Suspending and resuming processes
Providing mechanisms for process synchronization
Providing mechanisms for process communication
Providing mechanisms for deadlock handling

The operating system is responsible for the following activities in connection with process management:

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Memory Management

To execute a program all (or part) of the instructions must be in memory
All (or part) of the data that is needed by the program must be in memory.
Memory management determines what and when - in memory

Optimizing CPU utilization and computer response to users

Memory management activities

Keeping track of which parts of memory are currently being used and by whom
Deciding which processes (or parts thereof) and data to move into and out of memory
Allocating and deallocating memory space as needed

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Storage Management

OS provides uniform, logical view of information storage
Abstracts physical properties to logical storage unit - file
Files are stored in a number of different storage medium.

Disk – the various types of disk are - hard disk drive (HDD) containing a non-removable disk, the floppy disk drive (FDD), and various optical disc drives (ODD)
Flash Memory is an EEPROM (electronically erasable programmable read-only memory) form of memory which does not require a power source to retain the data. It’s a data-storage medium used with computers and other electronic devices.
Tape - is a data storage device that reads and writes data on a magnetic tape.

Each medium is controlled by device drivers (i.e., disk drive, tape drive)

Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random)

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File System Management

Files usually organized into directories
Access control on most systems to determine who can access what
OS activities include

Creating and deleting files and directories
Primitives to manipulate files and directories
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage media

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Secondary-Storage Management

Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time
Proper management is of central importance
Entire speed of computer operation hinges on disk subsystem and its algorithms
OS activities

Free-space management
Storage allocation
Disk scheduling

Some storage need not be fast

Tertiary storage includes optical storage, magnetic tape
Still must be managed – by OS or applications

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��Device Management, Security, �I/O System Management ��

Device Management: Device management keeps tracks of all devices. This module also responsible for this task is known as the I/O controller. It also performs the task of allocation and de-allocation of the devices.

Security: Security module protects the data and information of a computer system against malware threat and authorized access.

I/O System Management: One of the main objects of any OS is to hide the peculiarities of that hardware devices from the user.

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Command Interpretation, Networking, Job Accounting, Communication Management

Command interpretation: This module is interpreting commands given by the user and acting on system resources to process that commands.
Networking: A distributed system is a group of processors which do not share memory, hardware devices, or a clock. The processors communicate with one another through the network.
Job accounting: Keeping track of time & resource used by various job and users.
Communication management: Coordination and assignment of compilers, interpreters, and another software resource of the various users of the computer systems.

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Services of Operating System

Operating systems provide an environment for the execution of programs.
Operating systems provides certain services to:

Programs
Users of those programs

Basically two types of services:

Set of operating-system services provides functions that are helpful to the user:
Set of operating-system functions for ensuring the efficient operation of the system itself via resource sharing

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OS Services Helpful to the User

File-system manipulation - Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management.
Communications – Processes may exchange information, on the same computer or between computers over a network

Communications may be via shared memory or through message passing (packets moved by the OS)

Error detection – OS needs to be constantly aware of possible errors

May occur in the CPU and memory hardware, in I/O devices, in user program
For each type of error, OS should take the appropriate action to ensure correct and consistent computing
Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system

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OS Services for Ensuring Efficient Operation

Resource allocation - When multiple users or multiple jobs are running concurrently, resources must be allocated to each of them

Many types of resources - CPU cycles, main memory, file storage, I/O devices.

Accounting - To keep track of which users use how much and what kinds of computer resources
Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other

Protection involves ensuring that all access to system resources is controlled
Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts