Explain the structure of the operating systems.

We all are addicted to using computers but we all never really bother to known what is actually there inside it i.e., who is operating the whole system. Then something inevitable occurs. Your computer system crashes and the machine is not able to boot. Then you call a software engineer and he tells you that the operating system of the computer has to be reloaded. You are of course familiar with the term operating system but you know what it is exactly. 

About Operating System

- Operating system is the software that actually gives life to the machine. 

- Basic intelligence is the requirement of every computer system to start with. 

- Unlike we humans, computers do not have any inborn intelligence. 

- This basic intelligence is required because this is what the system will use to provide essential services for running the programs such as providing access to various peripherals, using the processor and allocation of memory and so on. 

- One type of service is also provided by the computer system for the users. 

- As a user, you may require to create, copy or delete files. 

- This is the system that manages the hardware of the computer system. 

- It also sets up a proper environment in which the programs can be executed. 

- It is actually an interface between the software and the hardware of the system.

- On booting of the computer, the operating system is loaded in to the main memory. 

- This OS remains active as long as the system is running. 

Structure of Operating Systems

- There are several components of the operating system about which we shall discuss in this article.

- These components make up the structure of the operating system.

1. Communications: 

- Information and data might be exchanged by the processes within the same computer or different computers via a network. 

- This information might be shared via memory if in the same computer system or via message passing if through some computer network. 

- In message passing, the messages are moved by the operating system.

2. Error detection: 

- The operating system has to be alert about all the possible errors that might occur. 

- These errors may occur anywhere ranging from CPU to memory hardware devices in the peripheral devices in the user application. 

- For all types of error, proper action must be taken by the operating system for ensuring that correct and consistent computing takes place. 

- The users and the abilities of the programmers are enhanced greatly by the debugging facilities.

3. Resource allocation: 

- Resources have to be allocated to all of the processes running. 

- A number of resources such as the main memory, file storage, CPU cycles etc have some special allocation code while other resources such as I/O devices may have request and release codes.

4. Accounting: 

- This component is responsible for keeping the track of the computer resources being used and released.

5. Protection and Security: 

- The owners of data and information might want it to be protected and secured against theft and accidental modification.

- Above all, there should be no interference of the processes with working of each other. 

- The protection aspect involves controlling the access to all the resources of the system. 

- Security involves ensuring safety concerning user authentication in order to prevent devices from invalid attempts.

6. Command line interface or CLI: 

- This is the command interpreter that allows for the direct entry of the command. 

- This is either implemented by systems program or by the kernel.

- There are a number of shells also for multiple implementations.

7. Graphical User Interface: 

This is the interface via which the user is actually able to interact with the hardware of the system. 

What is multi-tasking, multi-programming and multi-threading?

When it comes to computing, there are 3 important tasks that are inter-related concepts namely multi-programming, multitasking and multi-threading. 

What is Multitasking?

- This has actually emerged out of the need of multitasking since while the system performed one task a lot of time was wasted. 

- As their needs grew,people wanted the computer to perform many tasks at the same time. Multi-tasking is what we call it. 

- Here, multiple tasks or processes are carried out simultaneously.

- The common processing resources i.e., the main memory and the CPU are shared by these processes. 

- If the system has only one CPU to work with, then it can only run one task at a time. 

- Such systems seek to multi-task by scheduling all the processes required to be carried out. 

- It runs one task and the other one waits in the pipeline.

- The CPU is reassigned to all the tasks turn by turn and this is termed as a context switch. 

- When this happens very frequently, it gives an illusion that the processes are being executed in parallel. 

- There are other systems called multi-processor machines which have more than one CPU and can perform a number of tasks greater than the number of CPUs. 

- There are a number of scheduling strategies that might be adopted by the operating systems and they are:

Ø  Multi – programming

Ø  Time – sharing

Ø  Real – time systems

What is Multi-Programming?

- Earlier we had very slow peripheral devices and therefore the CPU time was a luxury and so expensive. 

- Whenever a program was being executed for accessing a peripheral, the CPU was to keep waiting for the peripheral to finish with processing the data. 

- It is very inefficient. 

- Then came the concept of multi–programming which was a very good solution. 

-  When the program reached the waiting status, its context was stored in the memory and the CPU was given some other program to execute. 

- This processing continued till all the processes at hand were completed. 

- Later,developments such as VMT or virtual machine technology and virtual memory greatly increased the efficiency of the multi – programming systems. 

- With these two technologies the programs were able to make use of the OS and the memory resources just as they were being used by the currently executing programs. 

- However, there is one drawback with multi–programming which is that is does not guarantees that all programs will be executed in a timely manner. 

- But then also it was of a great help in processing multiple batches of programs.

What is Multi-threading?

 

- With multi–tasking a great improvement was seen in the throughput of the computer systems. 

- So programmers found themselves implementing programs in sets of cooperating processes.

- Here, all the processes were assigned different tasks like one would take input, other one would process it and a third one would write the output to the display. 

- But for this, there was a requirement of tools that allowed an efficient exchange of the data.

- Threads were an outcome of the idea that the processes can be made to cooperate efficiently if their memory space is shared.

- Therefore, threads can be defined as the processing running in a memory context that is same for all. 

- These threads are said to be light – weight since there is no need for a change of memory context for switching between them. 

- The scheduling followed here is of the preemptively. 

What are different aspects of network testing?

Network is interconnected collection of hardware components and computers interconnected by communication channels which shares data and resources. Computers are said to be interconnected if they are capable of sharing data and information. These computers are said to be autonomous since no computer can start, stop and control the other computer.

NEED OF NETWORK
- Network is needed because through network we can share resource which means we can make all programs, data and peripherals available to anyone on the network irrespective of the physical location of the resources and user.
- It provides reliability i.e.a file can have copies on two or three different machines, so if one of them is not available ,the other copies can be used.
- It also affects the cost factor which means personal computer have better price/performance ratio then the micro computers.
- Using a network, it is possible for managers, working far apart, to prepare financial report for the company.
- The changes at one end can be noticed at another and hence it speeds up the co-operation among them.

Network has some disadvantages also.
- Network makes systems more sophisticated and complex to run.
- This can add to costs and you may need a specialist staff to run the network. - If software and files are held centrally, it may be impossible to carry out any work if the central server fails.
- If networks are badly managed services can become unusable and productivity fails.
- File security is more important especially if connected to WAN e.g. protection from viruses.

Network testing is done by various types of tools. These tools help us to test switches, routers, servers and other networks. Network testing aims at determining the strength of the integrity of the network.


- Network testing methodology aims at testing the networking equipments and live networks.
- Network testing requires the network to adhere to the standards of networking. - It doesn’t matter what the software testers test the network for inter- operability, scalability, performance or protocol conformance, they can always rely only network testing for in depth and un biased testing of the network.

Speed testing is another aspect of network testing.
- Speed test can be used to verify if the internet service provider is delivering the connection speed that they promised or not.
- These days network equipment face validation challenges.
- There is a dire need of improving the quality and the performance of the core product.
- While the network complexity is constantly increasing, the process of network testing is increasingly becoming more intricate and time consuming.

There are certain problems that arise while performing the network test. They have been listed below:


- The complex combination of software, firmware and hardware components makes it very difficult to test a particular device as a single integrated system. Such cases often require manual intervention.
- The streamlining of remote manufacturing processes not only makes the whole testing process more complicated but it also makes it difficult to meet the market requirements on time.
- Performing network testing across a wide variety of scripts, testing equipments and network protocols requires complex configuration processes and long set up.

Whether the network to be tested is WAN (wide area network), LAN (local area network), VPN (virtual private network, data center products or other networking devices, network testing over comes their validation challenges and at the same time it increases test automation coverage and provides massive reduction in overhead testing costs and time consumption.

These days automated network testing set up is available. It significantly reduces the test duration, coverage and optimized test operations. Such set ups offer complete automation and configuration of the test prior to testing. The created test cases confirm to standards and provide maximum flexibility and re-usability.

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.).
A standard hybrid network uses something called a hybrid access point, a networking device that both broadcasts a wireless signal and contains wired access ports. The most common hybrid access point is a hybrid router. The typical hybrid router broadcasts a Wi-Fi signal using 802.11 a, b or g and contains four Ethernet ports for connecting wired devices. The hybrid router also has a port for connecting to a cable or DSL modem via Ethernet cable.
There are several different possible network configurations for a hybrid network. The most basic configuration has all the wired devices plugged into the Ethernet ports of the hybrid router. Then the wireless devices communicate with the wired devices via the wireless router.
Computers aren't the only devices that can be linked over a hybrid network. You can now buy both wired and wireless peripheral devices like printers, Web cams and fax machines.

Hybrid network are: star ring network and star bus network
* A Star ring network consists of two or more star topologies connected using a multi-station access unit (MAU) as a centralized hub.
* A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone).

While grid networks have found popularity in high-performance computing applications, some systems have used genetic algorithms to design custom networks that have the fewest possible hops in between different nodes. Some of the resulting layouts are nearly incomprehensible, although they function quite well.