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.