Explain the various File Operations

A number of operations can be carried out on a file. However, there are 6 basic file operations. As we know a file is an ADT or abstract data type. Certain operations need to be considered for defining a file. Operating systems makes calls to these operations. 

Following are the six basic operations:

1. Creation of a file: 

- This operation involves two steps. 

- Firstly, a sufficient space has to be found for storing the file in the file system. - Secondly, for this new file an entry should be made in the directory.

2. Writing to a file: 

- For writing data to a file, a system call has to be made with name and the data to be written as its arguments. 

- A writer pointer is kept by the system at the location in the file where the next write operation is to be carried out. 

- This pointer is updated whenever a write operation occurs.

3. Reading from a file: 

- Just like the write operation, in order to read information from a file, a system call has to be generated along with the name of the file and the location of the content to be read as its arguments. 

- Here, instead of a write pointer there is a read pointer that will indicate the location where the next read operation is to take place. 

- The location at which the current operation is being carried out is kept as a “per – process current – file – position” pointer since the process is either writing to or reading from the file. 

- The same pointer can be used by both the read and write operations in order to reduce the complexity of the system as well as for saving space.

4. Re-positioning within a file: 

- System carries out search in the directory looking for the appropriate entry. 

- When found, the current file position pointer is re-pointed to this position. 

- This file operation does not require carrying out any input or output operation in actual. 

- Another name for this file operation is the file seek.

5. Deletion of a file: 

- For deletion of the file, the system searches through the directory to find the appropriate entry. 

- When found, the space held by this file is released and the entry in the directory is destroyed so that this space can be reused by other files.  

6. Truncating a file: 

- Sometimes you may require deleting only the contents of a file while keeping it attributes. 

- Deleting the file and recreating it is not an efficient solution. 

- This file operation lets you to erase the contents of the file but save its attributes.

- But here the length attribute of the file will be changed to zero after truncation. 

- The file space is released after truncating.

The above mentioned six basic file operations constitute the minimal file operations set. These operations are primary ones and if combined can perform some other secondary file operations such as copying. A table known as the open file table is maintained by the operating system that stores all the information about the files that are currently open. When the file is closed, its entry is deleted from the open file table. Some files have to be opened explicitly with the function open() before using it. The name of the file is passed as an argument to this function. Then it looks in the directory for this file and an entry is made in the open file table.  Each file has some access rights. It is in these access modes that a process uses the file. A process can perform only those operations which are permitted by the access rights of the file. 

Define a process? What are sequential and concurrent processes?

- Each and every task which we order our computer to carry out is accomplished by a set of processes. 

- It is these processes that actually run the program. 

- A process can be defined as an instance of the program that is currently being executed. 

- A program’s current activity and the code being executed are stored in the process itself. 

- However, it depends on the operating system that the process is to constitute of multiple threads for a concurrent execution or just one thread for sequential execution. 

This gives rise to two different types of processes namely:

Sequential processes 

Sequential processes can be executed on the same processor but the concurrent processors however may sometimes require more than one processor.

Concurrent processes

Concurrent processes are executed in parallel to each other and at the same whereas the sequential processes go step by step executing one instruction at a time. 

Concepts of Process

- A computer program can be defined as a set of passive instructions. When these instructions are actually executed, they form a process. 

- The same program may have a number of processes associated with it. 

- Multiple processes can be executed by sharing the processors and the resources. 

- If this is done, it is called multitasking. 

- Each processor takes up a single task. 

- With multitasking, switching between the different tasks becomes possible for the processor and so the processes won’t have to wait for long. 

- However, it depends entirely on the operating system when the switch has to be performed:

1. When the task is performing I/O operations or
2. When the task itself indicates that it can now be switched or
3. On hardware interrupts.

- Time sharing is a common type of multitasking and allows interactive user applications to response quickly. 

- In systems using the time sharing systems, switching is done quite rapidly. 

- This gives an illusion of the simultaneous execution of the multiple processes by the same processor. 

- Such type of execution is termed as concurrency.

- Direct communication that may take place between independent processes is avoided by many of the modern operating systems for the reasons of maintaining reliability and security. 

- The inter-process communication functionality is kept under strict control and mediation. 

- In general, the following resources are said to constitute a process:

Ø  Executable machine code’s image associated with the task.

Ø  Some part of virtual memory that is inclusive of the process specific data, executable code, heap and a call stack. Heap is for holding the immediate data generated during the execution and the call stack is for keeping a track of the subroutines.

Ø OS descriptors belonging to the resources that were allocated to the processes. These descriptors may be data sources, sinks and file descriptors etc.

Ø  Security attributes including the set of permissions for the process and the owner of the process.

Ø  Processor state like physical memory addressing or register contents etc. registers store the state during the execution of the process or otherwise it is stored in memory.

- Most of this information is held in the process control blocks regarding the active processes. 

- The operating system makes it a point to maintain a separation between its resources and allocate them the requested resources so that they won’t interfere with the working of each other and thus won’t cause any system failures such as thrashing or deadlocks. 

- But processes do require communicating with each other. 

- For such cases to make interaction safe, operating system has mechanisms especially for the inter-process communication.

What are different types of operating system?

Developing an operating system is one of the most complicated activities and favorite of most of the computing hobbyists. For a hobby OS, its code is not directly derived from the already existing Oss. Some entirely new concepts might also be included in the OS development. It may also start from modeling an existing one. Whatever the case maybe, the hobbyist is his own active developer. Application software might be developed specifically for an OS or hardware. Therefore, when the application has to be ported to some OS that may implement its required functionality differently, the application might be required to be changed, adapted or maintained. 

Types of Operating System

There are many types of operating about which we shall discuss in this article.

1. Real time operating system: 

- It is a multi – tasking OS aimed at the execution of the applications that are real time. 

-These operating systems work on scheduling algorithms written exclusively for them. 

- This is done so as to make them achieve a behavior that is deterministic in nature. 

- Their main objective is to give a quick response to the events that is also predictable in nature. 

- The design which is implemented is event driven and employs the idea of time sharing and sometimes both. 

- The system that is event driven switches among the different tasks according to the priorities assigned to them. 

- On the other hand, the systems following the time sharing methodology switch between the tasks based up on the clock interrupts.

2. Multi–user and single user operating systems: 

- In the multi–user operating systems the same computer system can be accessed by multiple users at the same time. 

- Systems that can be classified under the multi–user systems are the internet servers and the time sharing systems since using the time sharing principle they allow multiple users to access the system. 

- There are other types of operating systems that allow only one user to execute a number of programs simultaneously and are called the single – user operating systems.

3. Multi–tasking and single–tasking operating systems: 

- The operating systems that allow multiple programs to be executed simultaneously (as per the human time scales) are termed as the multi – tasking OS.

- In the single–taking OS, only one program can be run at a time. 

- Multi –taking can be done in the following two ways:

Ø  Pre–emptive multi –tasking: The CPU time is sliced and each of the time slots are given to each of the programs that are to be executed. This kind of multi–tasking is supported by the operating systems such as Linux, AmigaOS and Solaris.

Ø  Co–operative multi–tasking: Systems following this rely on one process for giving time to the other processors but in a pre–defined manner. This multi–tasking type was used by the MS windows 16 – bit version, Mac OS preceding OS X.

There are Oss that used to support both of these namely win9x and Windows NT.

4. Distributed operating system: 

- This kind of OS is used to manage a group of computers that are independent of each other and makes them seem like one single system.

- This OS led to the development of networked computers which could link to and communicated with one another.

- These computers in turn paved way for distributed computing. 

- They carried out computations on more than one computer. 

- Computers working in cooperation with each other, together make up a distributed system.

5. Embedded Operating System: 

It is used in embedded computer systems such as in PDAs.

What is an Operating System?

- A collection of small and large software that help in the management of the computer hardware resources is called an operating system. 

- As the term suggests it operates or drives the system. 

- The basic common services required by the computer programs are offered by this OS only. 

- Without an OS, the application programs would fail to function. 

- Operating systems are of many types. 

- One such type is the time sharing OS that schedules the tasks to be done so that the processor time, printing, mass storage and so on resources could be utilized efficiently. 

- It is an intermediate thing between the hardware and the user. 

- It is through the OS that you are able to actually communicate with the computer hardware. 

- Functions such as memory allocation and basic input output operations are dependent totally on the OS. 

- Even though the hardware directly executes the application code, it does frequently involve the OS or OS itself interrupts in between. 

- Any device containing a computer do has an OS such as video game consoles, mobile phones, web servers, super computers and so on.

- Some popular OS are:

Ø  Android

Ø  BSD

Ø  Linux

Ø  iOS

Ø  Microsoft windows

Ø  Windows phone

Ø  Mac OS X

Ø  IBM z/ OS

All the OS have relation with UNIX save windows and z/OS.

- Types of Operating systems are:

1. Real time OS
2. Multi – user OS
3. Multi – tasking OS
4. Single  - tasking OS
5. Distributed OS
6. Embedded OS

- It was in 1950 that the basic operating systems came in to existence such as parallel processing, interrupts and run time libraries.

- Assembly language was used for writing the UNIX OS. 

- There are many sub–categories in the Unix like family of the operating systems:

1. System V
2. BSD
3. Linux and so on.

- A number of computer architectures are supported by these Unix – like systems. 

- They come in heavy use in the following fields:

1. Servers in business
2. Work stations in academic
3. Engineering environments

- Few UNIX variants are available for free such as BSD, Linux etc. and are quite popular. 

- The holder of the Unix trademark is the open group and it has certified four Oss as Unix so far. 

- Two of the original system V Unix descendants are IBM’s AIX and HP’s HP – UX and they run only on the hardware provided by their manufacturer. 

- Opposite to these is the sun microsystem’s Solaris OS that can be used on different hardware types (inclusive of the Sparc and x86 servers etc. and PCs). - The POSIX standard was established to the sought the inter-operability of the Unix. 

- This standard is applicable for any OS now, even though originally it was developed especially for the variants of Unix.

- Berkeley Software Distribution or BSD family is a Unix sub–group. 

- It includes the following:

1. FreeBSD
2. NetBSD
3. OpenBSD

- The major use of all of these is in the web servers. 

- Furthermore, they are also capable of functioning as a PC OS. 

- BSD has made a great contribution in the existence of the internet. 

- Most of the protocols were refined and implemented in BSD. 

What is autonomic networking?

- The concept of autonomic networking follows directly from the automatic computing.

- The initiation of the autonomic computing was done by the IBM Corporation in the year of 2001.

- This concept has been brought in to the present world networking scenario in order to make the creation of self - managing networks possible. 

- Self managing networks are required for overcoming the complexity of the various networks (including internet) that is increasing at a very rapid pace. 

- This is also necessary for the further growth of the networks i.e., beyond the network size that we have today. 

- Autonomic networking is a means for the management of the network complexity. 

- In future, it is quite a possibility that routers could not be configured directly. - A point will come when it won’t be manageable by humans. 

- Autonomic networking will also minimize the manual intervention to a large extent plus it will also cut down the dependencies on the operator. 

- NMS intervention will also be reduced. 

- A fully – fledged autonomic network is expected to be capable of the following:

Ø  Self – configuration

Ø  Self – protection

Ø  Self – optimization

Ø  Self – healing

- In traditional networking systems, the amount of configuration, monitoring and reporting to be done is very large and amount of routing is very less. 

- In the autonomic networking systems, things are just the opposite i.e., there is less amount of intent, feedback and reporting and routing is more along with the other operations such as discovery and autonomic interactions. 

In autonomic networking, there are 3 characteristics of the administrator interface:

1. It is abstract
2. Light weight
3. Wide scope

- The increasing complexity of the network is viewed as a problem by most of the experts and that it might prove to be hindrance in its usability in the near future. 

- Number of PDAs, game consoles and smart phones is increasing day by day and these need an interconnection.

- Though such kind of pervasive computing adds features but it also increases the burden on the networking infrastructure that already exists since the number of tasks is so large that it is very difficult for humans to manage alone. - Another thing that adds to the problem is the cost of keeping a manual control on a number of devices in the infrastructure.

- Another important aspect is the price of manually controlling huge numbers

of vitally important devices of current network infrastructures.

- An analogy to autonomic nervous systems is the autonomic nervous system

or ANS. 

- This system regulates all the functions of the body and its various organs.

- Autonomic network systems bear a close resemblance to the ANS.

- Autonomic networking is all about adding more intelligence to the network.

- A number of complex operations are required to be carried out such as admission control, authentication, billing, shaping, routing, policing, QoS prioritizing and video encoding for providing simple services to the customer. 

There are a number of problems in the way of network as mentioned below:

1. The ever increasing size of the network.
2. The heterogeneous nature of the applications and devices.
3. Increase in the requirement of service quality.
4. Increase in the user expectations.
5. Ever changing requirements.
6. Changing context

- Pre – defined context is kept in while designing networks with the traditional approaches. 

- Whenever there is a change in the context, it leads to more time consuming manual tasks. 

- Algorithms used today do not have the ability of detecting context changes and interpreting the policies. 

- Such manual management causes more loss and outages in the revenue of the organization. 

- In autonomic networking, the system itself optimizes the goals. 

What is meant by Conditional Access System?

- Conditional access system or CAS is a system that has been developed as a means for providing the protection to content by setting certain criteria that should be met before the access to it is granted. 

- The concept of conditional access is however related closely to the digital television systems such as the satellite television. 

- The standards for the conditional access system have been defined under the following specification documents of the digital video broadcasting standard (DVB):

1. DVB – CA (conditional access)
2. DVB – CSA (common scrambling algorithm)
3. DVB – CI (common interface)

- All of these standards together define a method for obfuscating a digital television stream, thus providing access to only those possess the ‘valid description smart cards’. 

- All of these specifications are available on the standards page of the DVB web site.

- Conditional access is the result of combination of encryption and scrambling technologies. 

- Firstly, the data stream is subjected to scrambling with a secret key of 48 – bits usually called the control word. 

- The control word is generated in such a pattern in which the successive word cannot be predicted. 

- It is recommended by the DVB that a physical process should be used for that. 

- For a person to unscramble the data stream it is required that he/ she should know about the current control word. 

- In order to provide the protection to control word during the course of transmission, encryption methodology is used. 

- The control word will be de-crypted by the conditional access system only when there is authorization. 

- This authorization is given in the form of EMM or entitlement management message. 

- They are specific for each subscriber. 

- Different ECMs can also transmit the control word at one allowing the usage of many conditional access systems at once and simultaneously. 

- The simulscrypt of the DVB allows all the multiplex operators to cooperate while at the same time saves bandwidth. 

- Channels such as the hot bird satellites and the CNN international make use of several CASs in parallel. 

- The data from the decryption is read from the cards and updated if required through either of the following:

1. CAM or conditional access module
2. PC card – format card reader
3. Built – in ISO/ IEC 7816 card reader

- Conditional access systems include two major types namely analog systems and the digital systems both categorized at shown below:

1. Analog systems:

Ø  Nagravision

Ø  Videocrypt

Ø  Videocipher

Ø  Eurocrypt

2. Digital systems:

Ø  Abel Quintic

Ø  ABV (alliance broadcast vision)

Ø  Accessgate

- These systems are the key component for all the digital TV operations.

- Their purpose is to secure the investments of the operators through the encryption of the signals. 

- The payment from the customers in order to watch TV is also ensured by the conditional access systems. 

- But the TV operators usually have limited knowledge about the conditional access systems. 

- Encryption is involved with the whole conditional access system. 

- Operators have the analyzers for finding the cause of the common signal problems. 

- But they do lack tools that can debug the CASs. 

- Most of the conditional access system monitoring tools follow the ETSI TR 101 290 standard (a DVB promoted standard) even though the CAS is not fully covered by this specification. 

- Analyzing tools as such let the operators to know about the problems of conditional access system before the customers notice it. 

- But practically also, it is not possible to take care of all the problems that may affect the subscriber. 

What is Silk Test Architecture?

Whenever the graphical user interface of any software system or application is tested, a manipulation is done to the windows, menus, buttons and so on via input sources such as key board and mouse clicks etc. 

These windows, menus, buttons and so on are nothing but the GUI objects which are interpreted by the silk test. 

Later, in the test automation process the silk test recognizes these GUI objects based up on two things that uniquely identify them namely:

1. Object class properties and
2. Object methods

The operations that are performed on that particular application software by the users are usually in terms of input from keyboard and mouse clicks. 

These events are simulated by the silk test and the results thus obtained are subjected to automatic verification. 

This whole process is carried out by two very distinct components of the silk test mentioned below:

1. Silk host software and
2. Silk agent software

Both of these components are installed on different machines: the host machine and the target machine. 

- Host machine is for the silk host software whereas target machine is for the second component of the silk test. 

- The host component plays an important role in the development of the test scripts as well as the test plan.

- Using the components the following operations can be carried out on the test scripts:

1. Creating
2. Editing
3. Deleting
4. Compiling
5. Running
6. Debugging etc.

- The latter component of the silk test i.e., the agent is configured to interact with the graphical user interface of the AUT or application under test. 

- The agent is responsible for monitoring as well as driving the application under test. 

- The commands in test scripts are written in the 4test language. 

- These need to be translated in to specific equivalent GUI commands. 

- This task is also achieved by the silk agent software. 

- One thing that should be taken care of is that the application under test should be installed on the same machine as of the agent and on no machine else. 

- Matching objects to that of the GUI objects are created in the 4test and each one is unique. 

- Silk test completes test automation in a period of 4 steps:

1. Creation of a test plan
2. Recording of the test frame
3. Creation of the test cases
4. Execution of the test cases and interpretation of the test results.

- The interaction between the GUI of the application and the silk test is necessary since the operations need to be submitted to the application for simulation. 

- During the simulation, the silk test is said to be the simulated user whose work is to drive the application under test. 

- Since the AUT does not recognize the difference between the simulated user and the actual user, it behaves exactly in the same way as it reacts to an actual user. 

- In addition, you can have an agent as a local agent installed on the host machine. 

- Machines other than the host machine on which agent is installed in a network are called target machines. 

- The application under test is driven by the silk test and in turn drives the server like always. 

- Silk test is quite a powerful tool and can be used to drive the GUI of a server directly by running the scripts which will send equivalent SQL scripts to the data base of the server. 

- In such a way the server application is manipulated directly thus supporting the testing involving a server being driven by a client.

What is keyword view and Expert view in QTP?

In quick test professional you get two types of views namely the key word view and the expert view which we are going to discuss in this article. 

Keyword View in Quick Test Professional

- The key word view is more like a table like view which consists of a finite number of rows and columns. 

- Each row in the key word view represents a separate step. 

-On the other side, different parts of the steps are marked by the corresponding columns. 

- There is a separate column called the item column which holds the item on which the user wants the step to be carried out. 

- Also, in this column the hierarchy of the GUI object on which the operations are to be carried out. 

- There is another column by the name operation column consisting of the operations to be performed on the item as required. 

- One more column called value column holds the values of the arguments for the operation selected by the user. 

- Each step is documented by the quick test professional under the column titled documentation by the quick test professional for the ease of understanding. 

- The above mentioned 4 columns are the default columns provided by the quick test professional however comment and assignment columns in key word view can be used. 

- With the aid of key word view you can create as well as view the steps of the operation in a tabular, modular and key word driven format. 

- Full access is granted to the test automation experts via some debugging environment and integrated scripting that has round trip synchronizing with the key word view. 

Expert View and Differences between expert and keyword view in Quick Test Professional

- The expert view also displays the same object hierarchy all mapped to the same arguments value and same operation. 

- The basic difference lies between the formats in which the same data is arranged in the two. 

- Both have a distinct way of representing the data though the data displayed is same. 

- All the operations like creation of a step, modifying it and so on can be carried out in the key word view. 

- Expert view as the name suggests is a more advanced way of dealing with the data and requires mastery over the tool. 

- After all of the operations are recorded, they are displayed as steps in the quick test professional in key word view whereas these steps are generated as scripts in the expert view. 

- Expert view is for the advanced testers, using which they can view as well as edit their tests as and when required. 

- This also reveals the underlying standard of the VBscript that is used by the quick test professional. 

- Any changes that are made to the scripts in the expert view are automatically reflected in the key word view also.  

- However, in key word view the exact recording of the applications can be viewed. 

- In key word view, the steps can be created as well as viewed and can be modified by making a selection of the operations as well as items in the key word view and putting in the information as and where required. 

- In the expert view each of the operations that are performed in the form of VB script statements are displayed. 

- There exists a row in the key word view for every method and object. 

- To put it simply, it can be said that the VBscript format is used by the expert view whereas the scripts are represented using graphical user interface which is divided in to 4 default columns as mentioned earlier in the article in key word view. 

- Also, in the expert view all the test statements are displayed.