OPERATING SYSTEM CONCEPTS LINUX CONTENTS Need Services of

OPERATING SYSTEM CONCEPTS & LINUX

CONTENTS • Need & Services of Operating System • Simple Batch Systems • Multi Programmed Batched Systems • Time Sharing Systems • Parallel Systems • Distributed Systems • Real Time Systems

OPERATING SYSTEM DEFINITION • Operating system is software that is required in order to run application programs and utilities. • It works as a bridge to perform better interaction between application programs and hardware of the computer. • OS works as an interface between a user and computer hardware. • Operating system is system software that runs the computer and acts as a scheduler. (To be continued)

• The operating system provides a set of services to programs. • Users interact with the system through the system programs or through the application programs. • Various OS available are:

OPERATING SYSTEM NEEDS • To provide an interface between the hardware and the user. • To manage the hardware and software resources of the system. • To provide a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware. • To ensure that applications continue to run when hardware upgrades and updates occur. • To provide internal and external security. (To be continued)

• To load & schedule users program. • To control input & output. • To control program execution. • To manage use of main memory. • To make proper communication between user and hardware. • To start up the computer so that it can perform as per the user requirement.

OPERATING SYSTEM SERVICES • User Interface: - Command Line Interface or Graphical User Interface. • File management: - OS provides service to write new files or take input from some files - Involves secondary storage management. • Program Execution: -Provides an environment which involves the allocating and deallocating memory, CPU scheduling in case of multiprocessing. • Device Management: - The operating system manages I/O. (To be continued)

• Communication: - OS provides service of message passing between processes. • Security: - Internal: Protects the computer’s resources from the programs concurrently running on the system. - External: Protection from the network computers and users. • Resource Allocation and Accounting: - Allocates and keeps track of all the computer resources. • Error Detection: - OS constantly monitors the system for detecting the errors.

SIMPLE BATCH SYSTEMS • The problem of more setup time was reduce by processing the job’s in batches where similar job’s were submitted to the CPU for processing. • The system accepts various job’s from the users and place them in a waiting queue for getting CPU time(Spooling). • A batch operating system offers minimal functionality since it does not have to worry about the complications of sharing resources with multiple processes. • Batch processing operating systems are ideal in situations where: - There are large amounts of data to be processed. - Similar data needs to be processed. - Similar processing is involved when executing the data. (To be continued)

• Once the job loaded into primary memory, it competes for the processor. When the processor became available, the processor scheduler selects job that was loaded in the memory and execute it. • It helped in reducing the idle time of a computer system because job to job transition did not require operator intervention. • Another major time saving made possible by batch processing was reduction in set up time by operator by batching of similar jobs together.

MULTI-PROGRAMMED BATCH SYSTEMS • On multi programmed batch systems, jobs are read into a job pool stored on a disk. When one job is unable to execute because it is waiting for an I/O operation to complete, another job may be permitted to run. • Hence, it is possible for several jobs to share the time of the CPU. Supervisor Job A • Concurrently executing processes greatly increases operating system complexity as regards the sharing of computer resources. Job B Job C (Waiting for CPU time) (To be continued)

• Multiprogramming does not mean execution of instructions from several programs simultaneously. Rather it means that multiple programs are available to CPU and a portion of one is executed , then a portion of another and so on. • Requirements of Multiprogramming Systems - Large Memory - Memory Protection - Job status Preservation - Proper Job Mix - CPU Scheduling

TIME SHARING SYSTEMS - The operating system support an environment that allows programs to respond to user inputs in a reasonable amount of time. - The time sharing system provides the direct access to a large no. of user where CPU time is divided among the entire user on scheduler bases. - The time duration allocate to every user is known as Time Slice of Quantum. - The operating system not only to share resources among the various processes, but it creates the illusion that the processes are running simultaneously. - It does this by shifting execution rapidly among all the active processes. (To be continued)

• A time sharing system has many user terminals connected to the same computer simultaneously. • Advantages of Time Sharing Systems - Reduces CPU idle system - Quick response time - Good computing facility to small users • Modes of Time Sharing - Active Mode - Ready Mode - Wait Mode

PARALLEL SYSTEMS • These are primarily concerned with managing the resources of parallel machines. • It is a technique in which multiple operations are carried out simultaneously. • Parallelism reduces computational time. • There are four classes of processor architecture: - Single Instruction stream, Single Data stream (SISD) - Multiple Instruction stream, Single Data stream (MISD) - Single Instruction stream, Multiple Data stream (SIMD) - Multiple Instructions stream, Multiple Data stream (MIMD) (To be continued)

• The classification of parallel computing system is focused in terms of two independent factors - The number of data streams that can be simultaneously processed. - The number of instruction streams that can be simultaneously processed. • Parallel systems are more difficult to program than computers with a single processor because the structure of parallel computers varies accordingly and the processes of multiple CPUs must be coordinated and synchronized. • It is an evolution of serial computing where the jobs are broken into discrete parts that can be executed concurrently.

DISTRIBUTED SYSTEMS - It is a model where distributed applications are running on multiple computers linked through communications network. - It is designed for a connected, but independent, collection of computers that share resources such as hard drives. - A process can run on any computer in the network (presumably a computer that is idle) to increase that process's performance. - For example: LOCUS and MICROS. LOCUS OS made it possible to access local and distant files in uniform manner. Micros provided sharing of resources in an automatic manner.

REAL TIME OPERATING SYSTEM - Real time operating systems are very fast and quick respondent system. It is designed to provide execution support within the time constraints. - The computer processes immediately one or all the input and delivers the output instantly. - It is characterized by well-defined fixed-time constraints. Real-time systems may be either hard or soft real-time. - Extremely useful in applications like multimedia, virtual reality, online share trading etc. requiring advanced operating-system features. (To be continued)

- The primary function of real time operating system is to manage certain system resources such as the CPU, memory and time. - Each resource must be shared among the competing processes to accomplish the overall function of the system. - Examples: Airline reservation system Air traffic control system Defence application systems Banking