OS Exam 1

Advantages of Batch Processing

Batch processing takes much of the work of the operator to the computer. Increased performance as a new job get started as soon as the previous job is finished, without any manual intervention.

Security −

By means of password and similar other techniques, it prevents unauthorized access to programs and data.

The time sharing operating system uses

CPU scheduling and multiprogramming to provide each user with a small portion of a time. Computer systems that were designed primarily as batch systems have been modified to time-sharing systems.

Disadvantages of Multiprogramming

CPU scheduling is required. To accommodate many jobs in memory, memory management is required.

Errors can occur anytime and anywhere. An error may occur in

CPU, in I/O devices or in the memory hardware.

The advantages of network operating systems are as follows −

Centralized servers are highly stable. Security is server managed. Upgrades to new technologies and hardware can be easily integrated into the system. Remote access to servers is possible from different locations and types of systems.

Coordination between other softwares and users −

Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems.

A file represents

a collection of related information. Computers can store files on the disk (secondary storage), for long-term storage purpose. Examples of storage media include magnetic tape, magnetic disk and optical disk drives like CD, DVD. Each of these media has its own properties like speed, capacity, data transfer rate and data access methods.

A real-time system is defined as

a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment.

Protection refers to

a mechanism or a way to control the access of programs, processes, or users to the resources defined by a computer system.

Multiprogramming assumes

a single shared processor. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute.

A process is

basically a program in execution. The execution of a process must progress in a sequential fashion. A process is defined as an entity which represents the basic unit of work to be implemented in the system.

Considering a computer system having multiple users and concurrent execution of multiple processes, the various processes must

be protected from each other's activities.

A computer program is a

collection of instructions that performs a specific task when executed by a computer. When we compare a program with a process, we can conclude that a process is a dynamic instance of a computer program.

When a program is loaded into the memory and it becomes a process, it can be

divided into four sections ─ stack, heap, text and data.

Batch operating systems users

do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator.

Hard real-time systems

guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.

Popular Operating Systems

include Linux, Windows, OS X, VMS, OS/400, AIX, z/OS, etce

Main Memory

is a large array of words or bytes where each word or byte has its own address

Operating System

is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.

Operating System

is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers

Time Sharing Operating Systems

is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. It is a logical extension of multiprogramming. Also termed as, processor's time which is shared among multiple users simultaneously.

Operating System

is an interface between a computer user and computer hardware

A file system

is normally organized into directories for easy navigation and usage. These directories may contain files and other directions.

The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems

is that in case of Multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.

When a process executes,

it passes through different states. These stages may differ in different operating systems, and the names of these states are also not standardized. In general, a process can have one of the following five states at a time.

To speed up processing in Batch systems

jobs with similar needs are batched together and run as a group. The programmers leave their programs with the operator and the operator then sorts the programs with similar requirements into batches.

A distributed environment refers to

multiple independent CPUs or processors in a computer system.

Multitasking is when

multiple jobs are executed by the CPU simultaneously by switching between them. Switches occur so frequently that the users may interact with each program while it is running.

A file system is

normally organized into directories for easy navigation and usage. These directories may contain files and other directions.

A program is a

piece of code which may be a single line or millions of lines. A computer program is usually written by a computer programmer in a programming language.

Main Memory

provides a fast storage that can be accessed directly by the CPU. For a program to be executed, it must in the main memory.

Spooling refers to

putting data of various I/O jobs in a buffer. This buffer is a special area in memory or hard disk which is accessible to I/O devices.

Memory Management

refers to management of Primary Memory or Main Memory

The OS handles

routing and connection strategies, and the problems of contention and security.

A Network Operating System

runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions.

In case of distributed systems which are a collection of processors that do not

share memory, peripheral devices, or a clock, the operating system manages communications between all the processes. Multiple processes communicate with one another through communication lines in the network.

Spooling is an acronym for

simultaneous peripheral operations on line.

Batch processing is a

technique in which an Operating System collects the programs and data together in a batch before processing starts.

Interactivity refers to

the ability of users to interact with a computer system.

A process includes

the complete execution context (code to execute, data to manipulate, registers, OS resources in use).

in a transaction processing,

the processor executes each user program in a short burst or quantum of computation. That is, if n users are present, then each user can get a time quantum. When the user submits the command, the response time is in few seconds at most.

The primary purpose of the network operating system is

to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks.

In case of multi-user or multi-tasking environment, resources such as main memory, CPU cycles and files storage are

to be allocated to each user or job.

Distributed systems

use multiple central processors to serve multiple real-time applications and multiple users. Data processing jobs are distributed among the processors accordingly.

Operating systems handle many kinds of activities from

user programs to system programs like printer spooler, name servers, file server, etc. Each of these activities is encapsulated as a process.

Real-time systems are

usually dedicated, embedded systems.

The processors communicate with one another through

various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function. These processors are referred as sites, nodes, computers, and so on.

A real-time operating system must have

well-defined, fixed time constraints, otherwise the system will fail.

Real-time systems are used

when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application.

An operating system does the following activities related to spooling −

Handles I/O device data spooling as devices have different data access rates. Maintains the spooling buffer which provides a waiting station where data can rest while the slower device catches up. Maintains parallel computation because of spooling process as a computer can perform I/O in parallel fashion. It becomes possible to have the computer read data from a tape, write data to disk and to write out to a tape printer while it is doing its computing task.

Advantages of Multiprogramming

High and efficient CPU utilization. User feels that many programs are allotted CPU almost simultaneously.

The disadvantages of network operating systems are as follows −

High cost of buying and running a server. Dependency on a central location for most operations. Regular maintenance and updates are required.

An I/O subsystem comprises of

I/O devices and their corresponding driver software. Drivers hide the peculiarities of specific hardware devices from the users.

An Operating System manages the communication between user and device drivers. What does it do?

I/O operation means read or write operation with any file or any specific I/O device. Operating system provides the access to the required I/O device when required.

Process Scheduling

In multiprogramming environment, the OS decides which process gets the processor when and for how much time.

An operating system does the following activities related to real-time system activity.

In such systems, Operating Systems typically read from and react to sensor data. The Operating system must guarantee response to events within fixed periods of time to ensure correct performance.

An Operating System provides services to both the users and to the programs. It provides:

It provides programs an environment to execute. It provides users the services to execute the programs in a convenient manner.

Job accounting −

Keeping track of time and resources used by various jobs and users.

An Operating System does the following activities for file management −

Keeps track of information, location, uses, status etc. The collective facilities are often known as file system. Decides who gets the resources. Allocates the resources. De-allocates the resources.

An OS does the following activities for device management −

Keeps tracks of all devices. Program responsible for this task is known as the I/O controller. Decides which process gets the device when and for how much time. Allocates the device in the efficient way. De-allocates devices.

An Operating System does the following activities for memory management −

Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use. In multiprogramming, the OS decides which process will get memory when and how much. Allocates the memory when a process requests it to do so. De-allocates the memory when a process no longer needs it or has been terminated.

An Operating System does the following activities for processor management −

Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller. Allocates the processor (CPU) to a process. De-allocates processor when a process is no longer required.

Multiprogramming is

Sharing the processor, when two or more programs reside in memory at the same time

Algorithm

A part of a computer program that performs a well-defined task

Ready

The process is waiting to be assigned to a processor. Ready processes are waiting to have the processor allocated to them by the operating system so that they can run. Process may come into this state after Start state or while running it by but interrupted by the scheduler to assign CPU to some other process.

Software

A collection of computer programs, libraries and related data

Disadvantages of Batch Processing

Difficult to debug program. A job could enter an infinite loop. Due to lack of protection scheme, one batch job can affect pending jobs.

Advantages of Spooling

The spooling operation uses a disk as a very large buffer. Spooling is capable of overlapping I/O operation for one job with processor operations for another job.

The problems with Batch Systems are as follows −

Lack of interaction between the user and the job. CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU. Difficult to provide the desired priority.

Following are the major activities of an operating system with respect to program management −

Loads a program into memory. Executes the program. Handles program's execution. Provides a mechanism for process synchronization. Provides a mechanism for process communication. Provides a mechanism for deadlock handling.

Important function of an Operating System

Memory Management Processor Management Device Management File Management Security Control over system performance Job accounting Error detecting aids Coordination between other software and users

Examples of network operating systems include

Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.

Response time

The time taken by the system to respond to an input and display of required updated information

In a time sharing OS, the user can receive an immediate response because

Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently

Terminated/Exit

Once the process finishes its execution, or it is terminated by the operating system, it is moved to the terminated state where it waits to be removed from main memory.

Running

Once the process has been assigned to a processor by the OS scheduler, the process state is set to running and the processor executes its instructions.

Disadvantages of Time-sharing operating systems are as follows −

Problem of reliability. Question of security and integrity of user programs and data. Problem of data communication.

Waiting

Process moves into the waiting state if it needs to wait for a resource, such as waiting for user input, or waiting for a file to become available.

Error detecting aids −

Production of dumps, traces, error messages, and other debugging and error detecting aids.

Following are a few common services provided by an operating system −

Program execution I/O operations File System manipulation Communication Error Detection Resource Allocation Protection

Following are the major activities of an operating system with respect to file management −

Program needs to read a file or write a file. The operating system gives the permission to the program for operation on file. Permission varies from read-only, read-write, denied and so on. Operating System provides an interface to the user to create/delete files. Operating System provides an interface to the user to create/delete directories. Operating System provides an interface to create the backup of file system.

Advantages of Timesharing operating systems are as follows −

Provides the advantage of quick response. Avoids duplication of software. Reduces CPU idle time.

An Operating system does the following activities related to interactivity −

Provides the user an interface to interact with the system. Manages input devices to take inputs from the user. For example, keyboard. Manages output devices to show outputs to the user. For example, Monitor. The response time of the OS needs to be short, since the user submits and waits for the result.

Control over system performance −

Recording delays between request for a service and response from the system.

An OS does the following activities related to multiprogramming.

The operating system keeps several jobs in memory at a time. This set of jobs is a subset of the jobs kept in the job pool. The operating system picks and begins to execute one of the jobs in the memory. Multiprogramming operating systems monitor the state of all active programs and system resources using memory management programs to ensures that the CPU is never idle, unless there are no jobs to process.

Stack

The process Stack contains the temporary data such as method/function parameters, return address and local variables.

Following are the major activities of an operating system with respect to error handling −

The OS constantly checks for possible errors. The OS takes an appropriate action to ensure correct and consistent computing.

An operating system does the following activities related to batch processing −

The OS defines a job which has predefined sequence of commands, programs and data as a single unit. The OS keeps a number a jobs in memory and executes them without any manual information. Jobs are processed in the order of submission, i.e., first come first served fashion. When a job completes its execution, its memory is released and the output for the job gets copied into an output spool for later printing or processing.

An operating system does the following activities related to distributed environment −

The OS distributes computation logics among several physical processors. The processors do not share memory or a clock. Instead, each processor has its own local memory. The OS manages the communications between the processors. They communicate with each other through various communication lines.

Following are the major activities of an operating system with respect to protection −

The OS ensures that all access to system resources is controlled. The OS ensures that external I/O devices are protected from invalid access attempts. The OS provides authentication features for each user by means of passwords.

Following are the major activities of an operating system with respect to resource management −

The OS manages all kinds of resources using schedulers. CPU scheduling algorithms are used for better utilization of CPU.

An OS does the following activities related to multitasking −

The user gives instructions to the operating system or to a program directly, and receives an immediate response. The OS handles multitasking in the way that it can handle multiple operations/executes multiple programs at a time. Multitasking Operating Systems are also known as Time-sharing systems. These Operating Systems were developed to provide interactive use of a computer system at a reasonable cost. A time-shared operating system uses the concept of CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared CPU. Each user has at least one separate program in memory. A program that is loaded into memory and is executing is commonly referred to as a process. When a process executes, it typically executes for only a very short time before it either finishes or needs to perform I/O. Since interactive I/O typically runs at slower speeds, it may take a long time to complete. During this time, a CPU can be utilized by another process. The operating system allows the users to share the computer simultaneously. Since each action or command in a time-shared system tends to be short, only a little CPU time is needed for each user. As the system switches CPU rapidly from one user/program to the next, each user is given the impression that he/she has his/her own CPU, whereas actually one CPU is being shared among many users.

Text

This includes the current activity represented by the value of Program Counter and the contents of the processor's registers.

Heap

This is dynamically allocated memory to a process during its run time.

Start

This is the initial state when a process is first started/created.

Data

This section contains the global and static variables.

The advantages of distributed systems are as follows −

With resource sharing facility, a user at one site may be able to use the resources available at another. Speedup the exchange of data with one another via electronic mail. If one site fails in a distributed system, the remaining sites can potentially continue operating. Better service to the customers. Reduction of the load on the host computer. Reduction of delays in data processing.

Following are the major activities of an operating system with respect to communication −

Two processes often require data to be transferred between them Both the processes can be on one computer or on different computers, but are connected through a computer network. Communication may be implemented by two methods, either by Shared Memory or by Message Passing.

Soft real-time systems

are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.