The Common Types of Computer Virus

The Common Types of Computer Virus

Boot viruses

 The boot record program loads the operating system in the memory at startup. These viruses replace the boot record and move it to a different part of the hard disk, or simply overwrite it. To avoid loading the boot record viruses into memory, you must boot your operating system from another source .

Program viruses

These types of computer virus will infect only executable files  Once executed, these programs load into memory, along with the virus contained within them. Once in the memory, the scenario repeats – the virus is free to act and infect other files or simply deliver its payload. These viruses are friendlier than boot viruses and can be removed a lot easier.

Multipartite viruses

These computer viruses are hybrids, derived from boot viruses and program viruses. They infect executable files, just like the program viruses but, once the executable is executed, it infects the master boot records. The scenario is similar to the boot virus’s one: once you boot your operating system, the virus is loaded into the memory, from where it is free to infect other programs and replicate itself, ultimately delivering the payload.

Stealth viruses

These viruses are specialized in avoiding detection and will use a number of techniques to do so. Most of them simply redirect the hard disk head, forcing it to read another memory sector instead of their own. Some of them also alter the reading of the file size shown when listing the directory. These types of computer virus are very hard to find by humans, but antivirus software is specially designed to track them down and erase them.

Polymorphic viruses

The polymorphic viruses will always change their source code from one infection to another. Each infection is different, and this makes detection very hard. However, detection is still possible, depending on the antivirus.

Macro viruses

This virus is relatively new and it infects macros within a template or document. When you open a word processing document, it activates the virus. The virus infects the Normal.dot template, which is a general file used by all the documents. So, whenever you open an uninfected document, by referring to the Normal.dot file, it gets infected as well. This infection can only spread if infected documents are opened on another machine.

Active X viruses

Most people do not know how to configure ActiveX and Java controls, unconsciously leaving a security hole. Applets are then allowed to run freely on the machine, delivering all ActiveX viruses. By simply turning off some ActiveX and Java controls in the browser, a user can efficiently protect their PC from this type of computer virus.

Distributed Operating System

Distributed Operating System 

• A distributed operating system is one that looks to its users like an ordinary centralized operating system but runs on multiple independent CPUs. 
• The key concept here is transparency. The use of multiple processors should be invisible to the user. 
• Another way of expressing the same idea is to say that user views the system as virtual uniprocessor but not as a collection of distinct machines. 

• Distributed operating systems have many aspects in common with centralized ones but they also differ in certain ways. 
• Distributed operating system, for example, often allow programs to run on several processors at the same time, thus requiring more complex processor scheduling algorithms in order to achieve maximum utilisation of CPU's time.

• Fault-tolerance is another area in which distributed operating systems are different. 
• Distributed systems are considered to be more reliable than uniprocessor based system. 
• They perform even if certain part of the hardware is malfunctioning. 

Advantages of Distributed Operating Systems

There are three important advantages in the design of distributed operating system:

1. Major breakthrough in microprocessor technology: Micro- processors have become very much powerful and cheap, compared with mainframes and minicomputers, so it has become attractive to think about designing large systems consisting of small processors. These distributed systems clearly have a price/performance advantages over more traditional systems.

2. Incremental Growth: The second advantage is that if there is a need of 10 per cent more computing power, one should just add 10 per cent more processors. System architecture is crucial to the type of system growth, however, since it is hard to give each user of a personal computer another 10 per cent.

3. Reliability: Reliability and availability can also be a big advantage; a few parts of the system can be down without disturbing people using the other parts; On the minus side, unless one is very careful, it is easy for the communication protocol overhead to become a major source of inefficiency.
Protection: In a true distributed system there is a unique UID for every user, and that UID should be valid on all machines without any mapping. In this way no protection problems arise on remote access to files; a remote access can be treated like a local access with the same UID. There is a difference between network operating system and distributed operating system in implementing protection issue. In networking operating system, there are various machines, each with its own user to UID mapping but in distributed operating system there is a single systemwide mapping that is valid everywhere.

Program Execution: In the most distributed case the system chooses a CPU by looking at the processing load of the machine, location of file to be used etc. In the least distributed case, the system always run the process on one specific machine

An important difference between network and distributed operating system is how they are implemented. A common way to realise a networking operating system is to put a layer of software on top of the native operating system of the individual machines. 

Advantages of using the Internet

Advantages of using the Internet There are many advantages of using the Internet, such as : Global Audience Content published on the World Wide Web is immediately available to a global audience of users. This makes the World Wide Web a very cost-effective medium to publish information. Reaching more than 190 countries.  Operates 24 hours, 7  days  a week You don't need to wait until resources are available to conduct business. From a consumer's perspective as well as a provider's business can be consummated at any time. The fact that the Internet is operational at all times makes it the most efficient business machine to date.  Relatively Inexpensive It is relatively inexpensive to publish information on the Internet. At a fraction of the cost to publish information by traditional methods, various organizations and individuals can now distribute information to millions of users. It costs only a few thousand dollars to establish an Internet presence and publish content on the Internet.  Product Advertising It can use the World Wide Web to advertise various products.  Before purchasing a product, customers will be able to look up various product specification sheets and find out additional information.  It can use the multimedia capabilities of the World Wide Web to make available not only various product specification sheets but also audio files, images, and even video clips of products in action.   Distribute Product Catalogs The World Wide Web is a very effective medium for distributing product catalogs. In the old days, putting together a product catalog  used to be very costly in terms of time and money needed to publish and distribute it. The World Wide Web changes all this by allowing content developers to put together a sales catalog and make it available to  millions of users immediately. Furthermore,  unlike printed product catalogs that are usually updated around once a month, product catalogs on the World Wide Web can be updated as needed to respond to  various changing market conditions.  Online Surveys Traditional methods of performing surveys are often relatively slow and expensive compared to online surveys conducted on the Internet. Announcements With the World Wide Web, you can distribute various announcements to millions of users in a timely manner. Because there is virtually no time lag from the time it takes to publish information to making the information available to users, the Web is an ideal medium to publicize announcements. As more people discover the virtues of the Web and get connected to the Internet, the Web will become the medium of choice for many organizations and individuals to publicize various announcements.

Local Buses

Local Buses

• The performance of a microcomputer is often restrained by the relatively slow video cards and other peripherals, which cannot keep up with today's fast CPUs. 
• A local bus reduces the performance gap between the high-speed microprocessors and slower hard disks, video boards and other peripherals.
• Each bus hopes to boost microcomputer performance for I/O-intensive tasks. 
• They are two types of Local Buses. Namely 1) VL-Bus and a 2) PCI local bus.

o    VL-Bus : 

     

1.     VL-Bus specification was introduced by the VESA (Video Electronics Standards Association). 
2.      VL-Bus added peripheral components and connectors to the existing motherboard's 486 local bus and was available first. 
3.      Performance of the VL-Bus architecture declines sharply when supporting more than two devices, and the specification is currently limited to a 32-bit data path and 33-MHz operation. 
4.     This design is vanishing.

o    PCI (Peripheral Component Interconnect): 

1.      A PCI chip set adds a 64-bit-wide bus between the microprocessor and peripherals to offer a 64-bit data path. 
2.      This chip supports speeds of 66-MHz. 
3.      PCI can transfer data either 32- or 64-bits at a time. This architecture is developed by Intel, Compaq, DEC, IBM and NCR. 
4.     PCI technology incorporates a managing layer to route and manage data for efficient handling of high-speed data transfers between the microprocessor and peripherals.
5.     Its design goals are to produce a low-cost, high-performance interface and support future generations of peripherals. 
6.     PCI provides excellent compatibility, higher throughput and automatic configuration of peripheral cards. 
7.     PCI also has features such as expandability and plug-and-play flexibility.

o    Comparison: 

• Both technologies employ a microprocessor's local bus instead of the system input/output bus to rapidly exchange data between the processor and peripherals.
• The VESA design reached the market first and is less expensive than PCI, but PCI is technically superior. 
• A VL-Bus usually supports only two or three local-bus peripherals, while PCI can support up to 10 local buses. 
• PCI uses fewer bus lines than VL-Bus. This enables PCI to eventually cost less to manufacture. PCI is now dominating the market.

Buses

Buses

• A bus is a data pathway between several hardware components inside or outside a computer. 
• It not only connects the parts of the CPU to each other, but also links the CPU with other important hardware. 

• The other important hardware includes memory, a disk control unit, a terminal control unit, a printer control unit, and a communications control unit. 
• The capacity of a bus is expressed as bits. 
• A larger capacity bus is faster in data transfer.

Three Main Bus Architectures

o    ISA (Industry Standard Architecture): ISA is pronounced i- suh. This is the original PC bus architecture. It includes the 8-bit and 16-bit  buses in IBM personal computer series and compatibles. Now, it refers specially to the 16-bit AT bus.

o    MCA (Micro Channel Architecture): A 32-bit bus used in IBM P/S 2 series and other IBM models. This architecture allows multiprocessing that allows several processors to work simultaneously. Micro channel architecture is not compatible with PC bus architecture.

o    EISA (Extended Industry Standard Architecture): EISA is pronounced eesa. This is a bus standard for PCs that extends the AT bus  architecture to a 32-bit bus. This architecture also allows more than one CPU to share the bus. The purpose of EISA is to extend and amend the old ISA standard, so that all existing AT expansion boards can work with an EISA slot.

Types of Operating System

Types of Operating System

·    Batch Processing Operating System

• In a batch processing operating system interaction between the user and processor is limited or there is no interaction at all during the execution of work. 
• Data and programs that need to be processed are bundled and collected as a ‘batch’ and executed together.

Batch processing operating systems are ideal in situations where:

- There are large amounts of data to be processed.

- Similar data needs to be processed.

- Similar processing is involved when executing the data.

The system is capable of identifying times when the processor is idle at which time ‘batches’ maybe processed. Processing is all performed automatically without any user intervention.

·    Real-time Operating System

A real-time operating system processes inputs simultaneously, fast enough to affect the next input or process. Real-time systems are usually used to control complex systems that require a lot of processing like machinery and industrial systems.

·    Single User Operating System

A single user OS as the name suggests is designed for one user to effectively use a computer at a time.

·    Multi-Tasking Operating System

In this type of OS several applications maybe simultaneously loaded and used in the memory. While the processor handles only one application at a particular time it is capable of switching between the applications effectively to apparently simultaneously execute each application. This type of operating system is seen everywhere today and is the most common type of OS, the Windows operating system would be an example.

·    Multi-User Operating System

This type of OS allows multiple users to simultaneously use the system, while here as well, the processor splits its resources and handles one user at a time, the speed and efficiency at which it does this makes it apparent that users are simultaneously using the system, some network systems utilize this kind of operating system.

·    Distributed Operating System

In a distributed system, software and data maybe distributed around the system, programs and files maybe stored on different storage devices which are located in different geographical locations and maybe accessed from different computer terminals.

While we are mostly accustomed to seeing multi-tasking and multi-user operating systems, the other operating systems are usually used in companies and firms to power special systems.

Computer hardware

Computer hardware 

• Computer hardware is the physical component attached to your PC. 
• It can not be modified or changed regularly. 
• It is fixed to its place and requires complex examination in order to be rectified or repaired. 
• Computer hardware is entrenched inside a steel covering therefore it is not visible to the end users. 
• Computer hardware is of many different types and models. 

Features of Hardware

• Hardware has many components which are important to the working of the computer like software hardware devices. 
• The basic hardware of the computer is mother board, RAM and CPU. 
• However there are many different devices which are supporting the functioning of computer like mouse, data ports, monitor and removable storage devices. 
• The supporting hardware devices are divided into sub groups further like web cam, joystick, sound card and track ball etc. hardware is something which you can touch and feel and which cannot communicate with you. 
• Hardware is breakable or can be destroyed by external forces like shattered, hitting and electricity voltages.

Main Types of Computer Hardware

Computer hardware is divided into many different parts. 

• The most important types of computer hardware are mother board, central processing unit, random access memory, basic input output system, power supply, video display controller, computer bus and hard disk.  

• An alternate name to main board or system board, mother board is a central circuit, which is a complicated electronic board kept into computer for working as an electronic machine. 
• The next most important type of computer hardware is CPU. 
• Central processing unit seeks the software commands and interprets and process data. 
• Random access memory is the key component which allows the data to be reached in any form. 
• Next is the basic input output system, which loads and runs the software. Power supply takes electric current to the output load. 
• Video display controller helps in the logical conversion of the visual data in order to run a signal to be used by display medium. 
• Computer bus is used to transfer the data within the computer or with other computers. Hard disk is the stable that stores data and information on a magnetic surface, placed on hard disk platters.

Some other Supporting Hardware

• Some other types of hardware include CD ROM drive, Floppy disk and Zip drive. 
• The hardware such as Floppy drive is no more in use. 
• Floppy drive is a data storage device which was used to run a floppy. 
• This model of data transfer was slow and prone to viruses. 
• The data in the floppy gets contaminated even after two to three times. However it was an inexpensive way of carrying data. 
• CD ROM drives stands for compact disk read only memory. It is used to store data and software’s. 
• This important medium is the million dollar business for software producers. CD is run on the CD ROM.
• CD can carry data and software’s to the ultimate users. 
• The various applications which this device can carry are games, multimedia information, songs and movies. 
• Zip drive is medium capacity storage device which is removable.

Distributed Operating System

Distributed Operating System 

• A distributed operating system is one that looks to its users like an ordinary centralized operating system but runs on multiple independent CPUs. 
• The key concept here is transparency. In other words, the use of multiple processors should be invisible to the user. 
• Another way of expressing the same idea is to say that user views the system as virtual uniprocessor but not as a collection of distinct machines. 
• In a true distributed system, users are not aware of where their programs are being run or where their files are residing; they should all be handled automatically and efficiently by the operating system.

• Distributed operating systems have many aspects in common with centralized ones but they also differ in certain ways. 
• Distributed operating system, for example, often allow programs to run on several processors at the same time, thus requiring more complex processor scheduling  algorithms in order to achieve maximum utilisation of CPU's time.

• Fault-tolerance is another area in which distributed operating systems are different. 
• Distributed systems are considered to be more reliable than uniprocessor based system. 
• They perform even if certain part of the hardware is malfunctioning. 

Advantages of Distributed Operating Systems

There are three important advantages in the design of distributed operating system:

1. Major breakthrough in microprocessor technology: 

• Micro- processors have become very much powerful and cheap, compared with mainframes and minicomputers, so it has become attractive to think about designing large systems consisting of small processors. 
• These distributed systems clearly have a price/performance advantages over more traditional systems.

2. Incremental Growth: 

• The second advantage is that if there is a need of 10 per cent more computing power, one should just add 10 per cent more processors. 
• System architecture is crucial to the type of system growth, however, since it is hard to give each user of a personal computer another 10 per cent.

3. Reliability: 

• Reliability and availability can also be a big advantage; a few parts of the system can be down without disturbing people using the other parts; 
• On the minus side, unless one is very careful, it is easy for the communication protocol overhead to become a major source of inefficiency.

File System: 

• Distributed operating system supports a single global file system visible from all machines. When this method is used, there is one directory for executable programs one password file and so on. 
• When a program wants to read the password file it does something like
• Open (*/etc/password", READ-ONLY) 
• without reference to where the file is. 
• It is upto the operating system to locate the file and arrange for transport of data as they are needed.

• The convenience of having a single global name space is obvious.  

• When the user or program must specify the machine name, the system cannot decide on its own to move a file to a new machine because that would change the name used to access the file. 
• Thus in a network operating system, control over file placement must be done manually by the users, whereas in a distributed operating system it can be done automatically by the system itself. 

Protection: 

• In a true distributed system there is a unique UID for every user, and that UID should be valid on all machines without any mapping. 
• In this way no protection problems arise on remote access to files; a remote access can be treated like a local access with the same UID. 
• There is a difference between network operating system and distributed operating system in implementing protection issue. 
• In networking operating system, there are various machines, each with its own user to UID mapping but in distributed operating system there is a single systemwide mapping that is valid everywhere.

Program Execution:

•  In the most distributed case the system chooses a CPU by looking at the processing load of the machine, location of file to be used etc. In the least distributed case, the system always run the process on one specific machine
• An important difference between network and distributed operating system is how they are implemented. 

Real-time Systems

Real-time Systems

Real-time Systems: 

• It is another form of operating system which are used in environments where a large number of events mostly external to computer systems, must be accepted and processed in a short time or within certain deadlines. 
• Examples of such applications are flight control, real time simulations etc. Real time systems are also frequently used in military application.

• A primary objective of real-time system is to provide quick response times. User convenience and resource utilization are of secondary concern to real-dme system.
•  In the real-time system each process is assigned a certain level of priority according to the reletive importance of the even it processes.
•  The processor is normally allocated to the highest priority process among those which are ready to execute. 
• Higher priority process usually pre-emoted execution of lower priority processes. This form of scheduling called, priority based preemptive scheduling, is used by a majority of real-time systems.

Memory Management: 

• In real-time operating system there is a little swapping of program between primary and secondary memory. 
• Most of die time, processes remain in primary memory in order to provide quick response, therefore, memory management in real-time system is less demanding compared to other types of multi programming system. On the other hand, processes in real- time system tend to cooperate closely thus providing feature for both protection and sharing of memory.

I/O Management: 

• Time-critical device management is one of the main characteristics of real-time systems. It also provides sophisticated form of interrupt management and I/O buffering.

File Management: 

• The primary objective of file management in real-time systems is usually the speed of access rather than efficient utilization of secondary storage.Some embedded real-time systems does not have secondary memory. 
• However, where provided file management of real-time system must satisfy the same requirement as those found in time sharing and other multiprogramming systems.

Time Sharing System

Time Sharing System

•  It is a form of multiprocessing Operating system which operates in an interactive mode with a quick response time. 
• The user types a request to the computer through a keyboard. 
• The computer processes it and a response is displayed on the user's terminal. 
• A time sharing system allows the many users to simultaneously share the computer resources. Since each action or command in a time-shared system take a very small fraction of time, only a little CPU time is needed for each user. CPU switches rapidly from one user to another user, each user is given impression that he has his own computer, while it is actually one computer shared among many users.

• Most time sharing system use time-slice scheduling of CPU. 
• In this approach, Programs are executed with rotating priority that increases during waiting and drops after the service is granted. In Order to prevent a program from monopolising the processor, a program executing longer than the system defined time-slice in interrupted by the operating system and placed at the end of the queue of waiting program.

• Memory management in time sharing system Provides for the protection and separation of user programs. 
• Input/output management feature of time-sharing system must be able to handle multiple users.
• The processing of terminals interrupts are not time critical due to the relative slow speed of terminals and users. 
• As required by most multiuser environment allocation and reallocation of devices must be performed in a manner that preserves system integrity and provides for good performance.

• The words multiprogramming, multiprocessing and multitasking are often confused. 
• There are, of course, some distinctions between these similar, but distinct terms.

• The term multiprogramming refers to the situation in which a single CPU divides its time between more than one job. 
• Time sharing is a special case of multiprogramming, where a single CPU serves a number of users at interactive terminals.

• Multiprocessing, multiple CPUs perform more than one job at one time. 
• Multiprogramming and multiprocessing are not mutually exclusive. 
• Some mainframes and supermini computers have multiple CPUs each of which can juggle several jobs.

• The term multitasking is described any system that runs or appears to run more than one application program one time. 
• An effective multitasking environment must provide many services both to the user and to the application program it runs. 
• The most important of these are resource management which divides the computers time, memory and peripheral devices among competing tasks and interprocess communication, which lets tasking coordinate their activities by exchanging information.

Clipboard

Clipboard

Sometimes improperly referred to as the pasteboard, the clipboard is the location in a computer operating system such as Microsoft Windows that stores information that has been cut or copied from a document or other location. The clipboard will hold this information until it has been overwritten by new information. For example, a user may copy information from a word processor and paste that information into an e-mail message.

Many operating systems include software utilities known as clipboard viewers that enable a user to see what information is currently being stored in the clipboard, setup the clipboard with permissions, or view the history of the clipboard.  

How do I open the clipboard?

Windows 7 and Windows 8 users

Unfortunately Microsoft has decided to no longer included any clipboard viewer in Microsoft Windows 7 and Windows 8. In order to view the contents of the clipboard you need to download a third-party utility

how do I clear the clipboard.

Windows 2000 and XP users

Microsoft Windows 2000 and XP users may find it difficult to locate the clipboard because it has been renamed to the Clipbook viewer. It can be located by opening Windows Explorer, opening the "Winnt" or "Windows" folder, then the "System32" folder, and finally double clicking the clipbrd.exe. Users can also click Start, Run, typeclipbrd and press enter to execute this program.

Windows 9x, ME and NT users

Microsoft Windows 95, 98, NT 4.0, and ME come installed with a clipboard viewer that can be run by clicking Start, Programs, System Tools, and clicking Clipboard Viewer. The clipboard viewer is also executable through the clipbrd.exe file in the Windows directory.