REAL TIME SYSTEMS.

REAL TIME SYSTEMS:

A Real-Time system is used when there are rigid time requirements on the operation of a processor or the flow of data and is often used as a control device in a dedicated application.

1. A real time OS has well defined, fixed time constraints.

2. Processing must be done with in the defined constraints or the system will fail.

There are 2 flavours of Real-Time systems.

1. Hard Real-Time system.

2. Soft Real-Time system.

A Hard Real-Time system gurantees that critical tasks complete on time. This goal requires that all delays in the system be bounded, from the retrieval of stored data to the time that is takes it takes the facilities that are available in Hard Real-Time systems.

A less restrictive type of Real-Time system, where a critical Real-Time system task gets priority over other tasks... that priority untill if completes. As in hard Real-Time systems, kernel delays need to be bounded. A Real-Time task cannot be kept waiting identifitely for the kernal to run it.

DISTRIBUTED SYSTEM.

DISTRIBUTED SYSTEM:

The processors communicate with one another through various communicate lines, such as high speed buses or telephone lines.

These systems are usally reffered to as loosely coupled systems or distributed systems.

The processors in a distributed system vary in size and function. They include small microprocessors, work station, mini computers and larger general purpose computer system. These Processors are reffered to by a no. of different names such as site, modes, computers and so on.

There is variety of reasons for building distributed system, the major one are:

1. Resource Sharing:

If a no. of different sites are connected to one another then a user at one site may be able to use the resource available at another.

Example:

A user at site A may be using printer available at site B. Meanwhile, a user at site B may access a file that resides at A.

2. Computation speed up:

If a particular computation can be partitioned in to a no. of sub computations that can run concurrently then a distributed system may allow as to distribute the computation among the various sites to run that compution concurrently. In addition, if a particular site is currently overloaded with jobs, some of them may moved to other lightly loaded sites. This movement of job is called load sharing.

3. Reliability:

If one site facts in a distributed system, the remaining sites can potentialy continue operating.

4. Communication:

There are many instances in which programs needs to exchange data with one another on one system.

Example:

When many sites are connected by a communication network, the processes at different site the chance to exchange data. They may communicate via electronic mail. User can send to the user at the same site or at a different site.

DESKTOP SYSTEMS.

DESKTOP SYSTEMS:

Personal compuers PCs appeared in the 1970's. During this first decades, the CPUs in PCs lacked the features needed to protect an operating system from user programs. PC operating system therefore were neither multi user non multi tasking.

These system include PCs running microsoft windows and the apple macintosh. The MS-DOS operating system from microsoft has been superseded by multiple flavors of microsoft windows and IBM has upgraded MS-DOS to the OS/2 multi tasking system. The apple macintosh operating system has been ported to more advanced hardware and now includes new features, such as virtual memory and multi tasking operating.

COMMAND INTERPERITER.

COMMAND INTERPERITER:

One of the most importance system program for an operating system is the command ineterperiter which is the interface between the user and the operating system, same operating system in command interperiter in the conal.

The operating system by control statements when a new job is started in a batch system or when a user logs on to the Time share system. A program that reads and interupt control statement is executed automatically. This program is some time called control call interperiter and its aften known as the shell its function is simple to get the next command satement and execute it.

The mouse is moved to position the mouse pointer on images or icon on the screen that represents programs files and system function depending on the mouse pointer location clicking button on the mouse can invoke a program select a files and directory known as a folder or pull down a menu the contains commands.

PROTECTION SYSTEM.

PROTECTION SYSTEM:

Protection is any mechanism for controlling the access of programs, processors are users to the resources defined by a computer system. This mechanism for must provide means for specification of the controls to be impossed and means for enforcement.

Protection can improve reliability by detecting latend errors at the interfaces between components of system. Early detection of interface errors can aften prevent contamination of a healthy sub system by another sub system that is malfunctioning. An unprotect resources cannot defined against to use by an unauthoriside are incompetent user.

NETWORKING.

NETWORKING:

A distributed system is collection of processor that don't share memory peripheral device or a clock instead, each processor has its own memory and clock and the processor communicate with one another through various communication other such as high speed buses are networks.

The processor in the system are connected true a communication network, which can be configured in a number of different ways. The network may be fully or partialy connected. The communication network design must consider message routing and connection strategies and the problems of contention and security. The innovation of the world wide web was to create a new access method for information sharing. It improved on the existing file transfer protocal (FTP) and network file system protocal by removing the need for a user to login before she is allowed to use a remote resources. It defined a new protocal, Hyper text transfer protocal (http), for use in communication between a web server and web browser.

SECONDARY STORAGE MANAGEMENT.

SECONDARY STORAGE MANAGEMENT:

The main purpose of a computer system is to execute program. These programs with the data day access must be in main memory or primary storage during execution. Because main memory is too small to accommodate all data and programs and because the data that it holds are last when power is last the computer system must provide secondary storage to back up main memory most modern computer system use disk as the principle online storage medium for both programs and data.

The operating system is responsible for the following activities in connection with disk management.

* Free space management.
* Storage allocation.
* disk scheduling.

Because secondary storage is used frequently. It must be used in efficiently.

System component.

I/O System Management:

One of the purposes of an operating system is to hit peculierities of specific are the devices from the user. For example, in the unit the peculierities of I/O devices are hitten from the bulk of the operating system itself by the I/O sub system. The I/O sub system consist of,

* A memory management component that includes buffering, catching and spooling.

* A general device interface.

* Drivers for specific hardware devices.

System component.

FILE MANAGEMENT:

File management is a one of the most visible component of operating system. Computer can store information are several different types of physical media magnetic tape, magnetic disk and optical disk are the most common media. Each of disk media as its own charastric as it own physical organization. A file its a collections of related information define by its creator. Commonly files represented program and data. data files may be a numeric alphabetic or alpha numeric. Files may be a free from or may be a formated rigidly. A file consist of a sequence of bits, bytes line or records.

Whose meanings are define by the creators the concept of file is an extreamly general one.

File are normaly organized in to directory to is there use finally when multiple uses have access to a file. We may want to control by whom and it want ways - read, write, append files may be access.

* Creating and deleting a file.

* Creating and deleting directory.

* Supporting premitive for manipulating files and directory.

* Maping files on to secondary storage.

* Backing a file on stable storage media.

System component.

MEMORY MANAGEMENT:

Main memory is a large array of words or byte, ranging size of from hundreds or thousands to billion. Each words or bytes as it own address main memory is a repository of quick accessable data share by a CPU and I/O devices.

For a program to be executed it must be map to absolute address and locate in to memory as a program execute. It accesses the program instruction and data from memory by generating this absolute address. The program terminates it is memory spaces declared available and next the program can be loaded and executed.

* Keeping records of which parts of memory are currently used and by whom.

* Designing which process are to be loaded in to memory. When memory space became available.

* Allocating and deallocating memory space as needed.

System component.

System component:

Process management:

A process can be through out of programming execution a process needs certain resources including CPU time, memory files and I/O devices to accomplish its task the resources are either given to the process when its created or allocated to it while it is running.

A programming is a passive entity. Such as a content of file stored on disk, where as a process as on active entity. The program counter specified the next instruction to execute. The execution process must be a sequential.

* Creating and deleting both user and system processor.

* Susbonding and resuming.

* Providing mechanisms for process syncranization.

* Providing mechanisms for process communication.

* Provide mechanisms for dead lock handling.

TIME SHARING SYSTEM.

TIME SHARING SYSTEM:

The main disadvantage of multi programmed batch system is:

1. The user can interract with the job when its executing the user must setup the control cards to handle all possiable outcomes.

2. Another difficulty is that program must be debug statically from snapshop dumps. A programmer cannot modified program has it execute to study its behaviour.

Time sharing or multi tasking is logical expansion of multi prograamming. Multiple jobs are executed by the CPU switching between them. But the Switches occur so frequently that uses may interact with each program while it is running.

An intractive or hand on computer syste provides on time communication between the user and the system. The user given instruction to the use or to a program directly and receives an immediate response.

Time sharing where develope to provide interactive use of a computer system at a reasonable cost. A time shared operating system uses CPU scheduling and multi programming to provide each user with a small portion of a time shared computer.

A time shared operating system allows the many users to share the computer simultaneoualy. Since each action or command in a time shared system tends to be needed for each user.

The main disadvantage of Time sharing system is very difficult and expensive to built. Time sharing provids and on-line file system. The file system resides on a collection of disk. Hence memory management must be provided. It provides a mechanism for concurrent execution, which requires CPU scheduling schemes to orderly execution. The system should provides job synchronization and communication and that jobs should not gets struck in a dead lock, forever waiting for one another.

Multi programming and Time sharing are the control themes of modern operating system.

Multi Program Batch System.

The operating system picks and begins to execute one of the jobs in the memory. Eventually the job may have to wait for some task, such as tape to be mounted or an input and output operation to computer. In non-multi program system, the CPU would sit idle. In a multi-programming system. The operating system simply switches to and executes another job when that job needs to wait, the CPU is switched to another job. When that job needs to nob finishes waiting and gets the CPU back. As long as there is always some job to execute the CPU will never be idle.

Eg:- A lawyer does not have only one client at a time. Rather several clients may be in the process of being served at the same time. The process of being served at the same time. While one case is waiting to go trial or to have papers typed, the lawyer can work on another case. If the lawyer has enough client he never needs to be idle.

Multi programming is the first instance where operating system must make decisions for the users.

1. All the jobs that enter the system are kept in the job pool. This pool consists of all processes residing on mass storage awaiting allocated of main memory.

2. If several jobs are realy to be brought into memory but there is not enough memory for all of them then the system must choose a many them. Making this decision is job scheduling.

3. When the operating system a job from the job pool, it loads that job into memory for execution.

4. If several jobs are ready to run at the sametime, the system must choose among them and this decision is made b CPU scheduling which is discussed later.

Multi Program Batch System.


Student provides and important data structure: A job pool.

A job pool on discovers the OS to select which job run next, to increase CPU utilization.

1. When a job came in directly on cards on even or magnatic tape, It is not possible to run a job in a different order they must be runes sequently or FCFS (First Come First Serve).

2. When jobs are in direct access device. Such as it is disc job scheduling became possiable.

The most important aspect of job scheduling is a ability to multi program. Multi program mean increases CPU utilization by organizing jobs such that the CPU always has one to execute.

The idea is follows the operating system keeps several jobs in a memory at a time. The set of jobs is a subset of the job kept in the Job pool.

Operating system services.

* Program execution.

* I/O Operation.

* Files system manipulation.

* Communication.

* Error Reduction.

* Resource Alacation.

* Accounting.

* Protection.

Protection system.

* Security.

Networking.

* Client and sever.

I/O system management.

* A memory management component that includes

buffering, catching and spooling.

* A general device interface.

* Drivers for specified hardware devices.

Secondary storage management:

* Free space management.

* Storage alacation.

* Disk schduling.

File management.

* Creating and deleting a file.

* Creating and deleting directory.

* Supporting premitive for manifulating files &

directory.

* Maping files on to secondary storage.

* Backing a file an stable storage media.

Memory management.

* Keeping records of which parts of memory are

currently used and by whom.

* Designing which process are to be loaded in to

memory when memory space became available.

* Alacating and dealacating memory space as needed.

Process management.

* Creating and deleting both user and system

processor.

* Susbonding and resuming.

* Providing mechanisms for process sincranization.

* Providing mechanisms for process communication.

* Provide mechanisms for dead lock handling.

System Component!

1. Process management.

2. Memory management.

3. File management.

4. I/O management.

5. Secondary storage.

6. Networking.

7. Protection system.

8. Command interperiter.

Operating System!

1. Spooling uses the disk as a huge buffer, for reading as far a head as possible on I/P devices and for storing O/P files until O/P devices are able to accept them.

2. spooling is also used for processing data at remove sites.

3. spooling overlaps the I/O of one job with the computation of other jobs.

4. spooling has a direct beneficial effect on the performance of the system.

Thus spooling can keep both the CPU and I/P and O/P devices working at much higher rate.

Operating System!

Simple Batch Systems:

The Major Task of the OS is to transfer the control automatically from one job to the next. The OS will always reside in

memory.

To spend-up processing jobs with similar needs are batched together and were run through the computer as a group. The output

from each job would be sent back to the appropriate programmer. The programes will be stored in to batches with similar

requirements.

The definitive feature of a batch system is lack of interaction between the user and the job while that job is executing.

The job is prepared and submitted at later time, the output appears. The delay between job submission and job completion is

called tumaround time. May result from the amount of computing needed or from delays before the OS Stars to process the job.

In this execution enviroment, the CPU is often idle. This idleness occurs because the speeds of the mechanical input output

devices are slower than those of electronic devices.

Improvement is technology resulted in faster I/O devices unfortunately, CPU increased even faster, so that the problem was

not only unresolved, but also exacerbated.

The introduction of disk technology has improved the CPU speed. Rather than the cards being read from the card reader

directly into memory and then the job being processed, cards are read directly from the card reader on to the disk.

The location of card images is recorded in a table kept by the operating system, when a job is executed, OS satisfies its

requests for card reader i/p by reading from the disk. Eg. when the job that line is copied into a system buffer and is

called spooling the acronym for simuldaneous peripheral Operation on-line.

Operating System!

Types of systems:

1. Mainframe System.
*Batch System.
*Multiprogramed System.
*Time-sharing System.

2. Desktop System.

3. Multiprocessor System.

4. Distributed System.
*Client-Server System.
*Peer-to-Peer System.

5. Clustered System.

6. Real-Time System.

7. Hand held System.

Operating System!

An operating system is similar to Government. The components of computer system. Systems are hardware, software and datas.

The operating system provides the means for the uses of resources in the operation of the computer system. The operating

system perform no useful function by itself. It simply provides and enviromental with in which other program can do

successful work.

Operating System!

Goals:

1. Primary Goal:

The Primary Goal of operating system is those to make the computer system convinue to use.

2. Secondary Goal:

A secondary goal is used to the computer hardware in efficient manner.

Operating System!

purpose:

The purpose of operating system is to provide enviromental in which the user can execute the program.

Operating System!

Operating System:

Operating system is a program. That acts as an intermediatly between a user of computer and the computer hardware.