What is a computer? What are its major characteristics?

What is a computer? What are its major characteristics? 

 Binary Coded Decimal (BCD)

Binary Coded Decimal (BCD) is a method that uses binary digits 0 which represent “off” and 1 which represent “on”. BCD has been in use since the first UNIVAC Computer. Each digit is called a bit. Four bits are called a nibble and is used to represent each decimal digit (0 through 9).

The first binary number system was documented by Gottfried Leibniz in the 17th century. In 1854 mathematician George Boole came up with a system of logic that is know today as Boolean Algebra (based on two elements 0's and 1's).

The binary numbering system use a base of 2 whereas the decimal numbering system use a base of 10. When the binary number is 0, then the number is off, when the binary number is 1, then the number is on. The configuration of BCD is "8421" a 4 bit binary called a nibble . Therefore, the decimal 5 is a BCD 0101: where 0=8, 1=4, 0=2, 1=1; the 8 and 2 are turned off.

The following is an example of binary digits and how they represent decimal digits:

Decimal                 BCD

0                              0000

1                              0001

2                              0010

3                              0011

4                              0100

5                              0101

6                              0110

7                              0111

8                              1000

9                              1001

The advantage that Binary Coded Decimal (BCD) has over Binary is that there is no limit to number size. For every decimal number added, you add 4-bits or one nibble. Binary numbers are limited to the largest number that can be represented by 8, 16, 32 and 64 bits. It is easier to convert decimal numbers to and from BCD than Binary. BCD is usually converted to Binary for arithmetic processing since computers only process 0’s and 1’s. However, hardware can be built to operate directly with BCD. BCD is common in electronic systems where numeric value is displayed. This is done in systems that consist of digital logic and do not contain a microprocessor.

Computer processing requires a minimum of 1 byte (8 bits) therefore; the left portion of each BCD number is wasted storage. Because storage is valuable, storage can be saved by using packed BCD numbers. With packed BCD numbers (e.g. 2 bytes are use to store 3484 instead of 4 bytes) the left byte will consist of 00110100 (34) the right byte will consist of 10000100 (84).

Computer Chip

A computer chip is a small electronic circuit, also known as an integrated circuit, which is one of the basic components of most kinds of electronic devices, especially computers. Computer chips are small and are made of a semiconductor that is usually composed of silicon, on which several tiny components including transistors are embedded and used to transmit electronic data signals. They became popular in the latter half of the 20th century because of their small size, low cost, high performance and ease to produce.

The modern computer chip saw its beginning in the 1950s through two separate researchers who were not working together, but developed similar chips. The first was developed at Texas Instruments by Jack Kilby in 1958, and the second was developed at Fairchild Semiconductor by Robert Noyce in 1958. These first computer chips used relatively few transistors, usually around ten, and were known as small-scale integration chips. As time went on through the century, the amount of transistors that could be attached to the computer chip increased, as did their power, with the development of medium-scale and large-scale integration computer chips. The latter could contain thousands of tiny transistors and led to the first computer microprocessors.

There are several basic classifications of computer chips, including analog, digital and mixed signal varieties. These different classifications of computer chips determine how they transmit signals and handle power. Their size and efficiency are also dependent upon their classification, and the digital computer chip is the smallest, most efficient, most powerful and most widely used, transmitting data signals as a combination of ones and zeros.

Today, large-scale integration chips can actually contain millions of transistors, which is why computers have become smaller and more powerful than ever. Not only this, but computer chips are used in just about every electronic application including home appliances, cell phones, transportation and just about every aspect of modern living. It has been posited that the invention of the computer chip has been one of the most important events in human history. The future of the computer chip will include smaller, faster and even more powerful integrated circuits capable of doing amazing things, even by today’s standards.

Automated Teller Machine

ATM is a banking terminal that accepts deposits and dispenses cash. ATMs are activated by inserting a cash or credit card that contains the user's account number and PIN on a magnetic stripe. The ATM calls up the bank's computers to verify the balance, dispenses the cash and then transmits a completed transaction notice. The word "machine" in the term "ATM machine" is certainly redundant, but widely used.

Advantages of Automated Teller Machines:

• ATM provides 24 hours service
• ATM gives convenience to bank's customers
• ATM reduces the workload of bank's staff
• ATM provide service without any error
• ATM is very beneficial for travelers
• ATM may give customers new currency notes
• ATM provides privacy in banking transactions

Functions of ATM Machine

• Withdrawals
• Deposits
• Balance Inquiries

• Account transfer
• Utility bill pay (i.e. Cell phone recharge)
• Mini Statement Printing

P-N Junction

One of the crucial keys to solid state electronics is the nature of the P-N junction. When p-type and n-type materials are placed in contact with each other, the junction behaves very differently than either type of material alone. Specifically, current will flow readily in one direction (forward biased) but not in the other (reverse biased), creating the basic diode. This non-reversing behavior arises from the nature of the charge transport process in the two types of materials.

Fig: A p–n junction. The circuit symbol is shown: the triangle corresponds to the p side.

p–n junctions are elementary "building blocks" of most semiconductor electronic devices such as diodes, transistors, solar cells, LEDs, and integrated circuits; they are the active sites where the electronic action of the device takes place. For example, a common type of transistor, the bipolar junction transistor, consists of two p–n junctions in series, in the form n–p–n or p–n–p.

Local-Area Network (LAN)

A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building using network media. They function to link computers together and provide shared access to printers, file servers, and other services. LANs in turn may be plugged into larger networks, such as larger LANs or wide area networks (WANs), connecting many computers within an organization to each other and/or to the Internet.

Because the technologies used to build LANs are extremely diverse, it is impossible to describe them except in the most general way. Universal components consist of the physical media that connect devices, interfaces on the individual devices that connect to the media, protocols that transmit data across the network, and software that negotiates, interprets, and administers the network and its services. Many LANs also include signal repeaters and bridges or routers, especially if they are large or connect to other networks.

Major Characteristics of LAN

• Every computer has the potential to communicate with any other computers of the network
• High degree of interconnection between computers
• Easy physical connection of computers in a network
• Inexpensive medium of data transmission
• High data transmission rate

Use of LAN

Followings are the major areas where LAN is normally used

• File transfers and Access
• Word and text processing
• Electronic message handling
• Remote database access
• Personal computing
• Digital voice transmission and storage

Advantages of LAN

• Files can be stored on a central computer (the file server) allowing data to be shared throughout an organization.
• Workstations can share peripheral devices like printers. This is cheaper than buying a printer for every workstation.
• Networks also allow security to be established, ensuring that the network users may only have access to certain files and applications.
• Software and resources can be centrally managed.
• Network versions of software often allow for their speedy installation on workstations from the file server.
• Workstations do not necessarily need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PCs. Users can save their work centrally on the network file server. This means that they can retrieve their work from any workstation on the network. They do not need to go back to the same workstation all the time.
• The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers.
• Addition of new computer to network is easy
• High rate of data transmission is possible

Disadvantages

• If the communication line fails, the entire network system breaks down.
• Special security measures are needed to stop users from using programs and data that they should not have access to.
• Networks are difficult to set up and need to be maintained by skilled technicians.
• If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.
• Wired systems cannot be used in listed buildings.

• A fault in the network can cause user to lose the data
• It is difficult to make the system secure from hackers, novices or industrial espionage
• Decisions on resource planning tend to become centralized.
• Networks that have grown with little thought can be inefficient in the long term.
• As traffic increases on a network the performance degrades unless it is designed properly.
• The larger the network becomes difficult to manage

Wide Area Network

A Wide Area Network (WAN) is a network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, or national boundaries) using private or public network transports. Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations. In essence, this mode of telecommunication allows a business to effectively carry out its daily function regardless of location. The Internet can be considered a WAN as well, and is used by businesses, governments, organizations, and individuals for almost any purpose imaginable.

Numerous WANs have been constructed, including public packet networks, large corporate networks, military networks, banking networks, stock brokerage networks, and airline reservation networks. Some WANs are very extensive, spanning the globe, but most do not provide true global coverage.

Advantages of WAN

• Covers a large geographical area so long distance businesses can connect on the one network
• Shares software and resources with connecting workstations
• Messages can be sent very quickly to anyone else on the network. These messages can have pictures, sounds, or data included with them (called attachments).
• Expensive things (such as printers or phone lines to the internet) can be shared by all the computers on the network without having to buy a different peripheral for each computer.
• Everyone on the network can use the same data. This avoids problems where some users may have older information than others.
• Share information/files over a larger area
• Large network cover

Disadvantages of WAN

• Expensive and generally slow
• Need a good firewall to restrict outsiders from entering and disrupting the network
• Setting up a network can be an expensive and complicated experience. The bigger the network the more expensive it is.
• Security is a real issue when many different people have the ability to use information from other computers. Protection against hackers and viruses adds more complexity and expense.
• Once set up, maintaining a network is a full-time job which requires network supervisors and technicians to be employed.
• Information may not meet local needs or interests
• Vulnerable to hackers or other outside threats

Metropolitan Area Network

Metropolitan Area Network (MAN) is a computer network usually spanning a campus or a city, which typically connect a few local area networks using high speed backbone technologies. A MAN often provides efficient connections to a wide area network (WAN). There are three important features which discriminate MANs from LANs or WANs:

• The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km range. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings.
• A MAN (like a WAN) is not generally owned by a single organisation. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users.
• A MAN often acts as a high speed network to allow sharing of regional resources. It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Central Processing Unit (CPU)

At the “heart” of every computer lies the CPU, or central processing unit, which is responsible for carrying out arithmetic and logic functions as well as executing instructions to other components. The components of a CPU work together, and depending on how they are made, determine exactly how fast these operations can be carried out along with how complex the operations can be. Each of the separate components of a CPU on their own is relatively simple. Some of the primary components of a CPU, also known as a microprocessor, are the arithmetic logic unit (ALU), the control unit and the registers.

To begin with, the arithmetic logic unit is the part of the CPU that, as its name implies, carries out the mathematical functions of addition, subtraction, multiplication and division. It is often thought that these functions are all the CPU does in a computer, but this is not true. The ALU works along with, and as a major part of, the other components of a CPU to run many complex processes. A CPU can contain more than one arithmetic logic unit, and these ALUs can also be used for the purpose of maintaining timers that help run the computer.

The control unit is another fundamental part of the CPU. Essentially, it regulates the flow of information through the processor. The functions that a control unit performs can vary based on what a particular CPU was built to do. Mostly, this component receives, decodes, stores results and manages execution of data that flows through the CPU. More complex control units need to schedule when and how this great amount of information is to be processed and make sure that the data is sent to the correct components of the computer.

More components of a CPU that are vital to its operation are the registers, which are very small memory locations that are responsible for holding the data that is to be processed. The most important of these registers is known as the instruction pointer, which directs the CPU to the next memory location from where it is to receive information. Another type of register is the accumulator, which is responsible for storing the next values that will be processed by the CPU. Together all of these components of a CPU are becoming faster, more compact and more powerful as time goes on and technology advances.

EBCDIC

EBCDIC (Extended Binary Coded Decimal Information Code) is an eight-bit character set that was developed by International Business Machines (IBM). It was the character set used on most computers manufactured by IBM prior to 1981. EBCDIC is not used on the IBM PC and all subsequent "PC clones". These computer systems use ASCII as the primary character and symbol coding system.

EBCDIC is widely considered to be an obsolete coding system, but is still used in some equipment, mainly in order to allow for continued use of software written many years ago that expects an EBCDIC communication environment. It is the code for text files that is used in IBM's OS/390 operating system for its S/390 servers and that thousands of corporations use for their legacy applications and databases. In an EBCDIC file, each alphabetic or numeric character is represented with an 8-bit binary number (a string of eight 0's or 1's). 256 possible characters (letters of the alphabet, numerals, and special characters) are defined.

MICR

Magnetic ink character recognition, or MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing and clearance of cheques and other document. The MICR encoding, called the MICR line, is located at the bottom of a cheque or other voucher and typically includes the document type indicator, bank code, bank account number, cheque number and the amount, plus some control indicator. The technology allows MICR readers to scan and read the information directly into a data collection device. Unlike barcodes or similar technologies, MICR characters can be easily read by humans.

The use of MICR can enhance security and minimize the losses caused by some types of crime. If a document has been forged - for example, a counterfeit check produced using a color photocopying machine, the magnetic-ink line will either not respond to magnetic fields, or will produce an incorrect code when scanned using a device designed to recover the information in the magnetic characters. Even a legitimate check can be rejected if the MICR reader indicates that the owner of the account has a history of writing bad checks.

What is a computer? What are its major characteristics?

Definition: The term computer has been borrowed from compute that means to calculate. A computer is an electro mechanical device which has capacity to accept, store, process and retrieve data, according to the user requirements. Technically, a computer is a programmable machine. This means it can execute a programmed list of instructions and respond to new instructions that it is given.

Characteristics of a computer:

The following are the characteristics of a typical computer:

·         Speed: Present day computers operate at a very high speed. A computer can perform several million instructions in one second. For example, it can add or multiply 2,000,000 numbers in a second. There are several different types of computers and they all have different speeds ranging from high to very high. The speed of computers is specified in MIP (Million instructions per second).

·         Accuracy: Computers perform with a very high degree of consistent accuracy. Errors may occur due to a program logic error. These are human errors. Hardware errors are usually detected by the computer system itself. The probability of computer error is small and often traceable to faulty data. Computers rarely make mistakes and can accurately perform all kinds of complex computations.

·         Reliability: Computer systems are particularly adept at repetitive tasks. They do not take sick days and coffee breaks and they seldom complain. Computer systems are widely accepted because of their exceptional reliability. Unlike most humans they are capable of operating under most adverse conditions for extended periods of time without showing any signal of fatigue. Computers consistently provide the same accurate results under all operating conditions.

·         Memory Capabilities: Computer systems have total and instant recall of data and an almost unlimited capacity to store these data. A typical mainframe computer system will have many billions of characters, thousands of graphic images, stored and available for instant recall.

·         Versatility: The same computer can be used for various applications. For instance, a PC can be used to prepare a letter, prepare the balance sheet of company, store a database of employee, send/receive fax message etc. For a computer to perform a new job, all it needs is a program.

Computer now a days has become a driving force of way of life. None we can live a civil life without a computer. With trust and accuracy, this device run, protects, and revive the major systems in our daily life.

Describe the features of different generation of computers with example.

First Generation Computers:

The First Generation Computers was marked by the use of vacuum tubes for the electronic components and by the use of electrostatic tubes or mercury delay lines for storage. Examples of first generation computers are EDSAC (1949), EDVAC (1951) etc., this generation lasted until the end of the 1950s and the computers in this era had their basis in wired circuitry and thermion valves. Their outstanding features were:-

§  Very expensive, poor reliability, slow input/output.

§  Quite large, generated lot of heat and required special housing.

§  The medium of internal storage was magnetic drum.

§  Punched cards and paper tapes were used for secondary storage.

§  Continuous maintenance is required; produces lot of heat hence requires special air conditioning.

§  Applications-pay roll and other single applications in large companies.

§  Uses batch processing technology, to process the data.

Examples:

o    In 1949 – at Cambridge University EDSAC (Electronic Delayed Storage Automatic Calculator was developed).

o    In 1952 at Pennsylvania University, EDVAC (Electronic Discrete Variable Automatic Calculator) was developed.

o    In 1951, UNIVAC-I (Universal Automatic Computer) was developed.

Second Generation Computers:

The second-generation computers are initially marked by either magnetic drum or magnetic core storage and later by the use of the transistor in the place of vacuum tubes.
Main features of the second-generation computers are:

§  Magnetic core was used as primary storage device and tape as secondary storage.

§  Used transistor circuits, hence the size of the computer was small compared to that of first generation computer.

§  Greater reliability and higher speed, when compared to that of first generation computers.

§  Uses high level procedural languages viz., FORTRAN (Formula Translator) 1954-57, COBOL (Common Business Oriented Language) 1957-61.

§  They are small, faster and required less power to operate.

§  Applications: Payroll, Inventory, Accounts Receivable, in large and medium sized companies:

Ex: IBM 700, 1401; ATLAS; ICL 1901

Third Generation Computers (1965-1971):

The arrival of the third generation in the mid 1960’s proved to be an important milestone in the evolution of computers. The advances over the previous generations were very significant and allowed an increased number of organizations to reap the undoubted benefits which computerization could bring.

The following are the features of this generation:

§  Further reductions in size of computer.

§  The cost/performance factor has improved significantly.

§  Increased internal core memory capacity.

§  Processor speeds are rated in nano seconds.

§  The use of high-level languages became common e.g.: COBOL, FORTRAN and PL/I.

§  Multiprogramming operating system was developed.

§  Magnetic disk was used as secondary storage.

§  Transistors were replaced with integrated circuits – hence increased miniaturization.

§  Computers were capable of performing both scientific and business tasks with high speed and reliability.

§  Input and Output devices are improved.

§  Applications: Order Processing, air line reservation, real-time inventory control etc.

§  Uses online, real time processing and multiprogramming operating system.

Ex: IBM/360/370; NCR 395; Burroughs-B6500.

Fourth Generation Computers:

The fourth generation computers arrived in mid 1970’s. The distinguishing marks were the introduction of standard architecture, which proved greater mobility of the system. The introduction of micro technology and significant software developments, Micro technology gave rise to the development of microcomputers, work processors and intelligent terminals.

Features of this fourth generation are:

§  Integrated Circuits are replaced with very large-scale integrated circuits.

§  Semiconductors used as primary storage.

§  Dramatic decrease in the size of computer – development of microcomputers, personal computer.

§  Development of electronic spreadsheet.

§  Development of database management systems.

§  Development of distributed databases and virtual storage operating system.

§  Increased use of data communications and computer networks.

§  Increased use of Cathode Ray Tube (CRT) terminals.

§  The computers are compact, faster, and cheaper and are more reliable.

§  Application: Corporate modeling, decision support system, electronic funds transfer, electronic spread sheet, word processing and small business applications.

Future Computers (since 1985):

By the end of 1982, the computers were used every where, in automobiles, appliances, business information systems, and military hardware. With electronic technology advancing rapidly, the use of computers expected to grow in coming years. With the increased user requirements, the technology has evolved with outstanding features.

Some of the important features of the future computers are:

§  Future Computers use organic chips to process the data.

§  Both the software and hardware costs are decreasing at a high speed, so that the computers can be used by every common man (within the reach of common man).

§  Increased miniaturization and price/performance ratio.

§  The computers have high speed, and storage capacity.

§  Has the capacity to make decisions. (Auto decisions).

§  Uses non-procedural software, which is very user friendly.

§  Applications: Artificial Intelligence, Robots, Large Scale Corporate modeling, oil exploration, star wars system and personal robots.

 This is an open age for computer. Its gaining more and more superpower, being more sophisticated and convenient, and human being is going to be completely dependable on this human developed brain. 

Important Short Notes on Information Technology in Financial Services_DAIBB (Paper-4)

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme originally based on the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text. Most modern character-encoding schemes are based on ASCII, though they support many additional characters. It was only developed for communication and first adopted in 1963.

ASCII has been very popular in the computer world. It  contains seven bits to define each letter or character excluding eighth bit for error-checking function. There are 128 specific characters including capital letters, small letters, 0 to 9 digit, special symbols and some specific character having specific different functions.  Thirty-three codes  are used to represent things other than specific characters. The first 32 (0-31) codes represent a chime sound, used  to feed  line as well as to start of a header. The final code, 127 represents a backspace while the first 31 bits are the printable characters. Bits ranging from  48 to 57 represent the numeric digits and 65 to 90  represents the capital letters, while bits 97 to 122 are the lower-case letters. The rest bits represent symbols of punctuation, mathematical symbols, and other symbols such as the pipe and tilde.

Earlier ASCII was developed  only in six bits for a simpler character set. But  finally it has been reconstructed using seven bits for assimilating   lower-case letters, punctuation, and control character sets  to enhance its utility. No other than English characters  has been used in ASCII. ASCII is not used in IBM computers. IBM has its own built-in-code called EBCDIC code containing 256 character sets. Nowadays Unicode character set is replacing ASCII code very rapidly. ASCII is being famous in ASCII art phase that describes the use of the basic character set to create visual approximations of images.

'Personal Identification Number - PIN'

A personal identification number is a secret numeric password shared between a user and a system that can be used to authenticate the user to the system. Typically, the user is required to provide a non-confidential user identifier or token (the user ID) and a confidential PIN to gain access to the system. Upon receiving the user ID and PIN, the system looks up the PIN based upon the user ID and compares the looked-up PIN with the received PIN. The user is granted access only when the number entered matches with the number stored in the system. Hence, despite the name, a PIN does not personally identify the user.

PINs are most often used for automated teller machines (ATMs) but are increasingly used at the point of sale, for debit cards and credit cards. For example, when you take money out of an ATM, you enter your PIN number to prove that you're authorized to make the withdrawal. You might also enter a PIN number if you use your debit card at a retailer (only for POS transactions, not signature transactions).

UPS

Short for uninterruptible power supply, a power supply that includes a battery to maintain power in the event of a power outage. Typically, a UPS keeps a computer running for several minutes after a power outage, enabling you to save data that is in RAM and shut down the computer gracefully. Many UPSs now offer a software component that enables you to automate backup and shut down procedures in case there's a power failure while you're away from the computer.

There are two basic types of UPS systems: standby power systems (SPSs) and on-line UPS systems. An SPS monitors the power line and switches to battery power as soon as it detects a problem. The switch to battery, however, can require several milliseconds, during which time the computer is not receiving any power. Standby Power Systems are sometimes called Line-interactive UPSes.

An on-line UPS avoids these momentary power lapses by constantly providing power from its own inverter, even when the power line is functioning properly. In general, on-line UPSs are much more expensive than SPSs.

A UPS is typically used to protect computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 VA rating) to large units powering entire data centers or buildings

RDBMS

RDBMS stands for Relational Database Management System. RDBMS data is structured in database tables, fields and records. Each RDBMS table consists of database table rows. Each database table row consists of one or more database table fields. An important feature of relational systems is that a single database can be spread across several tables. This differs from flat-file databases, in which each database is self-contained in a single table.

RDBMS store the data into collection of tables, which might be related by common fields (database table columns). RDBMS also provide relational operators to manipulate the data stored into the database tables. Most RDBMS use SQL as database query language.

Relational database management system (DBMS) stores data in the form of related tables. Relational databases are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways.

RAM

RAM is an acronym for random access memory, a type of computer memory that can be accessed randomly; any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.

RAM is a temporary storage for data. For instance, when you open Microsoft Word (or any program), it goes into RAM because your CPU can get it a lot faster from RAM, than if it tried to get it off of your hard drive. However, RAM is dynamic which means if the power is cut off then any data that is in RAM is lost. Let’s say you are typing a letter, each time you hit the keyboard that data is put into RAM until it can be transferred to your hard drive. If the power goes off then whatever is in RAM while you were typing will be lost.

In common usage, the term RAM is synonymous with main memory, the memory available to programs. For example, a computer with 8MB RAM has approximately 8 million bytes of memory that programs can use. In contrast, ROM (read-only memory) refers to special memory used to store programs that boot the computer and perform diagnostics. Most personal computers have a small amount of ROM (a few thousand bytes). In fact, both types of memory (ROM and RAM) allow random access. To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only RAM.

Computer Virus

A computer virus is a computer program or piece of code that can replicate itself and spread from one computer to another. A computer virus is loaded onto computer without user’s knowledge and runs against his/her wishes. All computer viruses are man-made. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.

Types of Viruses

There are many types of computer viruses:

• File virus: Most viruses fall into this category. A virus attaches itself to a file, usually a program file.
• Boot sector virus: These viruses infect floppy and hard drives. The virus program will load first, before the operating system.
• Macro Virus: This is a new type of virus that use an application's own macro programming feature to distribute themselves. Unlike other viruses, macro viruses do not infect programs; they infect documents.
• Virus Hoax: Although there are thousands of viruses discovered each year, there are still some that only exist in the imaginations of the public and the press - known as virus hoaxes.

Disadvantages of computer virus

In the modern world our lives revolve around the computer and the internet. Without these it is simply not possible to envision a single day. We are totally dependent on the technology to get on with our regular activities. In such a scenario anything which threatens the data present in the computer is extremely debilitating indeed. Viruses can really make the life of computer users a living hell. Once they enter the system there is simply nothing to do but to rue the absence of a sturdy firewall. Virus remover programs are really the savior of all those whose lives are totally machine dependent.

Antivirus software has to be installed in the machine if you really give priority to the safety of the data stored there. A computer virus weakens the system, makes it prone to outside attacks of each and every kind. Not only that the machine slows down quite perceptibly and this increase with the length of time, the virus is allowed to remain inside. Virus and malware removal should become the utmost priority once you find that there is an uninvited guest present in your machine. Formatting followed by the addition of good antivirus software are some of the basic steps which need to be taken.

Phishing

Phishing is the act of attempting to acquire information such as usernames, passwords, and credit card details (and sometimes, indirectly, money) by masquerading as a trustworthy entity in an electronic communication. Phishing is a type of online identity theft. It uses email and fraudulent websites that are designed to steal one’s personal data or information such as credit card numbers, passwords, account data, or other information.

Phishing messages usually take the form of fake notifications from banks, providers, e-pay systems and other organizations. The notification will try to encourage a recipient, for one reason or another, to urgently enter/update their personal data. Such excuses usually relate to loss of data, system breakdown, etc.

Digital signature

A digital signature (standard electronic signature) takes the concept of traditional paper-based signing and turns it into an electronic "fingerprint.” This "fingerprint,” or coded message, is unique to both the document and the signer and binds both of them together. A digital signature ensures the authenticity of the signer. Any changes made to the document after it has been signed invalidate the signature, thereby protecting against signature forgery and information tampering. As such, digital signatures help organizations sustain signer authenticity, accountability, data integrity and the non-repudiation of signed electronic documents and forms.

Digital signature software is a powerful business tool that provides your customers, employees, vendors, and other partners the ability to fill out and sign documents online. Contracts, non-disclosure agreements, employment applications, forms, and dozens of other business documents can be executed in a web browser. This technology is secure, legally robust, and efficient, and saves all parties time, money, and hassle.

Many people use the terms “e-signature” and “digital signature” interchangeably. However, an electronic signature and a digital signature are two different types of consent, from both a legal and a technological perspective.

If a signature is digital, electronic, or written by hand on paper the old-fashioned way, the intent is the same. All three forms of signature indicate that the party signing a document agrees to the terms therein.

What Is a Website?

A website is a collection of web pages served from a single web domain. A web page is what you see on the screen when you type in a web address, click on a link, or put a query in a search engine. A web page can contain any type of information, and can include text, color, graphics, animation and sound. A website is hosted on at least one web server, accessible via a network such as the Internet or a private local area network through an Internet address known as

When someone gives you their web address, it generally takes you to their website's home page, which should introduce you to what that site offers in terms of information or other services. From the home page, you can click on links to reach other sections of the site. A website can consist of one page, or of tens of thousands of pages, depending on what the site owner is trying to accomplish.

Cache Memory

Cache memory is extremely fast memory that is built into a computer’s central processing unit (CPU), or located next to it on a separate chip. The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer. Whenever data must be passed through the system bus, the data transfer speed slows to the motherboard’s capability. The CPU can process data much faster by avoiding the bottleneck created by the system bus.

As it happens, once most programs are open and running, they use very few resources. When these resources are kept in cache, programs can operate more quickly and efficiently. All else being equal, cache is so effective in system performance that a computer running a fast CPU with little cache can have lower benchmarks than a system running a somewhat slower CPU with more cache. Cache built into the CPU itself is referred to as Level 1 (L1) cache. Cache that resides on a separate chip next to the CPU is called Level 2 (L2) cache. Some CPUs have both L1 and L2 cache built-in and designate the separate cache chip as Level 3 (L3) cache.

B. SWIFT

The Society for Worldwide Interbank Financial Telecommunication (SWIFT) provides a network that enables financial institutions worldwide to send and receive information about financial transactions in a secure, standardized and reliable environment. SWIFT also markets software and services to financial institutions, much of it for use on the SWIFTNet Network, and ISO 9362 bank identifier codes (BICs) are popularly known as "SWIFT codes".

SWIFT does not facilitate funds transfer; rather, it sends payment orders, which must be settled by correspondent accounts that the institutions have with each other. Each financial institution, to exchange banking transactions, must have a banking relationship by either being a bank or affiliating itself with one (or more) so as to enjoy those particular business features.

Founded in Brussels in 1973, the Society for the Worldwide Interbank Financial Telecommunication (SWIFT) is a co-operative organization dedicated to the promotion and development of standardized global interactivity for financial transactions. SWIFT's original mandate was to establish a global communications link for data processing and a common language for international financial transactions. The Society operates a messaging service for financial messages, such as letters of credit, payments, and securities transactions, between member banks worldwide. SWIFT's essential function is to deliver these messages quickly and securely -- both of which are prime considerations for financial matters. Member organizations create formatted messages that are then forwarded to SWIFT for delivery to the recipient member organization. SWIFT operates out of its Brussels headquarters and processes data at centers in Belgium and the United States.

Who Uses SWIFT?

Although originally the network was designed to support the requirements of Treasury and Correspondent banking operations, it has over the years allowed other institutions access to the services, albeit in some cases only to a limited degree. Currently the following types of organizations can access the service:

• Banks
• Trading Institutions
• Money Brokers
• Securities Broker Dealers
• Investment Management Institutions
• Clearing Systems and Central Depositories
• Recognised Exchanges
• Trust and Fiduciary Service Companies
• Subsidiary Providers of Custody and Nominees
• Treasury Counterparties
• Treasury ETC Service Providers
• Corporates

SWIFT operates a number of services, primarily;

1.    General Purpose Application, which only allows system messages, i.e. messages from a user to SWIFT and vice versa, not from one user to another.

2.    Financial Application, which is the user to user service comprising System Messages MT0nn, User-to-User Messages MT1nn through 9nn and Service Messages such as Acknowledgements.

Additionally, SWIFT provides a number of services that are charged for over and above the normal fees. A few of these are:

• IFT (Interbank File Transfer) -For bulk file transfer of messages, for example low net value, high volume retail payments.
• ACCORD - A centralised confirmation matching bureau service.
• Directory Services - An automated and centralised Standard Settlement Instruction service for message enrichment that at present is limited to Treasury and Payment information.
• RTGS (Y-copy) - Mostly used for sending a copy of a message or parts thereof to a third party, for example a Central Bank
• Country Specific (e.g. CREST, CHAPSEuro) - Where SWIFT are either the carrier of the messages or the supplier of additional network services.

Bangladesh Automated Clearing House (BACH)

BACH, the first ever electronic clearing house of Bangladesh, has two components -

• The Automated Cheque Processing System and
• The Electronic Funds Transfer.

Both the systems operate in batch processing mode – transactions received from the banks during the day are processed at a pre-fixed time and settled through a single multilateral netting figure on each individual bank’s respective books maintained with the Bangladesh Bank. A state-of-the-art Data Center (DC) and a Disaster Recovery Site (DRS) have been established comprising of most modern software and hardware for dealing with the operations of BACH. A Virtual Private Network (VPN) has been created between the participating commercial banks and Data Center (DC) & Disaster Recovery Site (DRS) for communicating necessary information related to BACH. Digital Certificate has been formulated for the first time in Bangladesh for secured data communication.

The automated clearinghouse (ACH) system is a nationwide network through which depository institutions send each other batches of electronic credit and debit transfers. The direct deposit of payroll, social security benefits, and tax refunds are typical examples of ACH credit transfers. The direct debiting of mortgages and utility bills are typical examples of ACH debit transfers. While the ACH network was originally used to process mostly recurring payments, the network is today being used extensively to process one-time debit transfers, such as converted check payments and payments made over the telephone and Internet.

The Reserve Banks and Electronic Payments Network (EPN) are the two national ACH operators. As an ACH operator, the Reserve Banks receive files of ACH payments from originating depository financial institutions, edit and sort the payments, deliver the payments to receiving depository financial institutions, and settle the payments by crediting and debiting the depository financial institutions' settlement accounts. The Reserve Banks and EPN rely on each other to process interoperator ACH payments--that is, payments in which the originating depository financial institution and the receiving depository financial institution are served by different operators. These interoperator payments are settled by the Reserve Banks.

 

Basics of ACH Payments

ACH payments are simply electronic transfers from one account to another. Common uses of ACH payments are:

• Customer pays service provider
• Employer deposits money to employee account
• Consumer moves funds from one bank to another
• Business pays supplier for products

Because they’re electronic, ACH payments use fewer resources (paper, ink, fuel to transport checks, etc). In addition, ACH payments make it easier to keep track of finances. Instead of generic check information on a bank statement, you see the other party’s name if you’ve used an ACH payment. Then it’s easier to categorize the transaction with your financial software.  ACH payments can be electronic from start-to-finish, or they can happen when a paper check is converted and processed electronically.

What is a Cheque Truncation System?

Cheque Truncation System (CTS) is a cheque clearing system for faster clearing of cheques. As the name suggests, truncation is the process of stopping the flow of the physical cheque in its way of clearing. In its place an electronic image of the cheque is transmitted with key important data.

Cheque truncation thus obviates the need to move physical instruments across branches. This effectively eliminates the associated cost of movement of physical cheques, reduces the time required for their collection and brings elegance to the entire activity of cheque processing. It is a system which is practiced worldwide in the banking sector.

Truncation means, stopping the flow of the physical cheques issued by a drawer to the drawee branch. The physical instrument is truncated at some point en route to the drawee branch and an electronic image of the cheque is sent to the drawee branch along with the relevant information like the MICR fields, date of presentation, presenting banks etc.

Cheque truncation, would eliminate the need to move the physical instruments across branches, except in exceptional circumstances. This would result in effective reduction in the time required for payment of cheques, the associated cost of transit and delays in processing, etc., thus speeding up the process of collection or realization of cheques.

What are the benefits of CTS to bank customers?

1. The main feature of the CTS 2010 cheque is that the physical movement of the cheque is stopped and the images of cheques are transmitted electronically thereby speeding up the process of cheque clearance and settlement between banks. This obviously means quicker clearance, shorter clearing cycle and speedier credit of the amount to your account.
2. With the movement of cheques from one bank to another having been stopped, there is no fear of loss of cheques in transit and chances of cheques being lost due to mishandling, etc are totally avoided.
3. At present clearing is restricted to banks operating within a city or within a restricted geographical area. Under the CTS, it is proposed to integrate multiple clearing locations managed by different banks in different centres so that cheques drawn on upcountry banks too can be cleared electronically without any geographical restrictions. Eventually, this will result in integration of clearing houses into a nation-wide standard clearing system, thereby making clearance of cheques drawn on any bank in India within 24 hours possible.
4. The cheques in transit are most susceptible to frauds and customers of banks are the worst sufferers in the present system of physical movement of cheques from one place to another.  Under the CTS system moving of physical cheques at different points is obviated as only electronic images are transmitted between banks, and this will considerably reduce the scope for perpetuation of frauds inherent in paper instruments.
5. With the introduction of homogeneity in security features under CTS standards 2010 such as embedded verifiable features like bar codes, encrypted codes, logos, watermarks, holograms, etc in every cheque leaf, it is now possible to detect frauds easily through interception of altered and forged instruments while passing through the electronic imaging system. This is expected to considerably reduce operational risks and risks associated with paper clearing for the benefit of all bank customers.
6. The CTS is expected to improve operational efficiency of the entire banking system, resulting in better customer service, improved liquidity position for banks’ customers and safe and secure banking for the entire banking public.

What are MICR, OMR and OCR?

MICR:

MICR stands for Magnetic-Ink Character Recognition. It is a special scanner. It reads the characters printed with magnetic ink and converts them into digital signals. These signals are then input to the computer for further processing. MICR devices are normally used in banks for processing cheques. MICR is used extensively in banking because magnetic-ink characters are difficult to forge and are therefore ideal for marking and identifying cheques.

OMR:

OMR stands for Optical Marks Recognition. OMR device is used to read handwritten marks or symbols printed on the paper. It uses a light beam to scan the marks and converts them into digital signals. These signals are then input to the computer for further -processing. OMR device is usually used in education field to check (or mark) the objective type answers of the questions.

OCR:

OCR stands for Optical Character Recognition. OCR device reads preprinted characters in a particular font and converts them into digital code. The characters printed on paper may be typewritten or handwritten. The OCR devices are commonly used to process utility bills and price code printed on the products in departmental stores.

Business continuity planning (BCP)

Business continuity planning (BCP) is a set of documents, instructions, and procedures which enable a business to respond to accidents, disasters, emergencies, and/or threats without any stoppage or hindrance in its key operations. It is also called business continuity and resiliency planning (BCRP). A business continuity plan is a roadmap for continuing operations under adverse conditions such as a storm or a crime.

Creating and maintaining a BCP helps ensure that your business has the resources and information needed to deal with an emergency. Other benefits include:

• Enhance your business image with employees, shareholders and customers by demonstrating a proactive attitude.
• Improve efficiency in the overall organization.
• Identify the relationship of assets both human and financial resources with respect to critical services and deliveries.

e-Governance

Several dimension and factors influence the definition of e-Governance. The word “electronic” in the term e-Governance implies technology driven governance. E-Governance is the application of Information and Communication Technology (ICT) for delivering government services, exchange of information communication transactions, integration of various stand-alone systems and services between Government-to-Citizens (G2C), Government-to-Business (G2B), Government-to-Government (G2G) as well as back office processes and interactions within the entire government frame work. Through the e-Governance, the government services will be made available to the citizens in a convenient, efficient and transparent manner. The three main target groups that can be distinguished in governance concepts are Government, citizens and businesses/interest groups. In eGovernance there are no distinct boundaries.

e-Government refers to government's use of information technology to exchange information and services with citizens, businesses, and other arms of government. e-Government may be applied by the legislature, judiciary, or administration, in order to improve internal efficiency, the delivery of public services, or processes of democratic governance. It also refers to the citizen to government interaction including the feed back of policiesThe primary delivery models are Government-to-Citizen or Government-to-Customer (G2C), Government-to-Business (G2B) and Government-to-Government (G2G) & Government-to-Employees (G2E). The most important anticipated benefits of e-government include improved efficiency, convenience, and better accessibility of public services.

Computer network

A computer network is a telecommunications network that connects a collection of computers to allow communication and data exchange between systems, software applications, and users. The computers that are involved in the network that originate, route and terminate the data are called nodes. The interconnection of computers is accomplished with a combination of cable or wireless media and networking hardware.

Two devices are said to be networked when a process in one device is able to exchange information with a process in another device. Networks may be classified by various characteristics, such as the media used to transmit signals, the communications protocols used to organize network traffic, network scale, network topology and organizational scope. The best-known computer network is the Internet.

Communication protocols define the rules and data formats for exchanging information in a computer network. Well-known communications protocols include Ethernet, a hardware and link layer standard that is widely used for local area networks, and the Internet protocol suite (TCP/IP), which defines a set of protocols for communication between multiple networks, for host-to-host data transfer, and for application-specific data transmission formats. Protocols provide the basis for network programming.

Advantages of Computer Network

• Networks allow data transmission among far areas also within local areas.

• Networks allow different users share the processing characteristics of different computers.

• Network allows users to share common set of data files and software stored in a main system.

• Network allows users to share common hardware resources such as printers, fax machines, modem etc.

• The cost of computing is reduced to each user as compared to the development and maintain of each single computer system.

One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:

• LAN - Local Area Network
• WLAN - Wireless Local Area Network
• WAN - Wide Area Network
• MAN - Metropolitan Area Network
• SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
• CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
• PAN - Personal Area Network
• DAN - Desk Area Network

LAN - Local Area Network

A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN - Wide Area Network

As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

LAN, WAN and Home Networking

Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP.

Other Types of Area Networks

While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:

• Wireless Local Area Network - a LAN based on WiFi wireless network technology
• Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.
• Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
• Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
• System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.

Encryption & Decryption

Encryption is the process of translating plain text data (plaintext) into something that appears to be random and meaningless (ciphertext). Decryption is the process of converting cipher-text back to plain text.

To encrypt more than a small amount of data, symmetric encryption is used. A symmetric key is used during both the encryption and decryption processes. To decrypt a particular piece of ciphertext, the key that was used to encrypt the data must be used.

The goal of every encryption algorithm is to make it as difficult as possible to decrypt the generated ciphertext without using the key. If a really good encryption algorithm is used, there is no technique significantly better than methodically trying every possible key. For such an algorithm, the longer the key, the more difficult it is to decrypt a piece of ciphertext without possessing the key.

It is difficult to determine the quality of an encryption algorithm. Algorithms that look promising sometimes turn out to be very easy to break, given the proper attack. When selecting an encryption algorithm, it is a good idea to choose one that has been in use for several years and has successfully resisted all attacks.

In today’s world Internet has touched each and every aspect of life changing the way we work, communicate and live. But the major concern has been about the security and privacy of the data that is being exchanged via Internet especially when you are sending the sensitive information through it.  Amongst many ways of securing data, encrypting the sensitive data is the most popular and effective way to have data security. Encryption is translation of data into a secret code called a cipher text. Decryption is the process of decoding data that has been encrypted into a secret format this requires secret code or password.

Computer encryption uses the science of cryptography. As the human-based code is too easy for a computer to crack, most of the encryption systems belong to the one of two categories.

1. Symmetric-key encryption:

In Symmetric-key encryption technique single key is used to encrypt and decrypt the message.

2. Public-key encryption:

While in public-key (or asymmetric) encryption technique, uses one key (private key) to encrypt a message while another key (public key) to decrypt the message. Public-key encryption uses the combination of a private key and a public key. The private key is kept secret and is only known to the person who encrypts the message, while the public key is freely disseminated which helps to verify the message. To decode an encrypted message, receiver uses the public key of the sender and his own private key.

Encryption/Decryption is advisable while carrying out any kind of sensitive transaction, such as a online purchases or the communication of a company sensitive documents between different departments in the organization etc. Encryption of the data ensures its secrecy and/or privacy.

Credit Card vs Debit Card

A debit card is either linked to a bank account or is a prepaid card. In either case, the card draws on funds that the consumer (owner of the card) has already deposited with a financial institution. On the other hand, a credit card is a kind of loan. When a consumer uses a credit card, the financial institution fronts to the consumer credit (a loan). Purchases are totaled and billed monthly and the user pays a few weeks after receiving the monthly bill.

Comparison chart

	Credit Card	Debit Card
Where money comes from?:	Borrowing money from a bank or financial institution. (Spending "other's" money)	Funds taken from the money that you have in your bank account. (Spending your "own" money)
Can be used as:	Credit card only	Debit Card and Credit Card
Line of Credit:	Carries Line of Credit	No Line of Credit
PIN Number:	No	PIN number provided, but not is not always asked to punch in.
Picture ID asked for:	Yes	No
Interest:	Pay additional interest drawn on the amount borrowed.	No
Credit History:	Responsible credit card usage and payment can improve one's credit rating. Credit cards typically report account activity to at least one of the three major credit bureaus on a monthly basis.	Does not affect credit history.
Legal Liability laws:	Strict. Consumer liability limit for credit card fraud is $50 if the credit card company is notified within 60 days in written since the fraudulent charges.	Lean. Consumer liability limit for debit card fraud is $50 if the bank is notified within two days of noticing the fraudulent charges.
Risk involved:	Low.	High, as they are attached to a bank account. A person does not need a pin number to use a debit card and therefore can easily drain a persons bank account, causing extreme problems.
Fraud:	Only problem is proving that someone else has used the card.	With a debit card the persons has to figure out how to get their money back and if any checks bounced they are responsible for those as well
Limit:	Credit line, which can be increased/decreased from the time of applying.	Equals your account limit.
Overdraw Fees:	Low.Some credit card companies allow to overdraw amount over the maximum credit line with a fees	High "overdraft" fees. Possible to overdraw amount over the account limit
Connected to:	Need not be connected to any bank account.	Checking Account;Savings Account
Monthly bills:	Yes	No
Offers Protection:	Yes. Example insurance on a rental car	No
Alternate payment type:	cash	cheque & cash

Advantages and Disadvantages of ATM Machines and Bank/Debit Cards 

	Advantages	Disadvantages
Debit Card	You don’t have to carry cash around with you. If your card is stolen, the thief cannot get your money without your PIN. You can use it to pay at some retail shops. Keeps your money safe.	If you forget your PIN number you cannot use the card. The system can be off-line. Training is needed. Difficult to maintain spending discipline.
ATM or Bank Card	You can withdraw cash at any time, day or night. The banks don’t need to be open. ATMs offer the convenience of multiple locations. You can withdraw cash at any bank that is part of the system to which your ATM card is linked. Your ATM card is protected by a PIN, keeping your money safe. You don’t need to fill out withdrawal and deposit slips as is required at the bank. ATMs are faster than going to the bank—no long lines. You can withdraw cash at ATMs in foreign countries.	ATM may be off-line (system down). You may forget your PIN number. Risk of robbery when you leave the ATM. The ATM can break down or run out of cash. Fees charged to use ATMs of other banks can become expensive.

ADVANTAGES & DISADVANTAGES OF AN ATM

Advantages of an ATM:

1. An automated teller machine increases existing business:

2. An automated teller machine generates new business:

3. An automated teller machine provides additional revenue streams :

4. An automated teller machine reduces risk and lowers costs:

Disadvantages:

1. Not available in remote places.

2. Cannot avoid illegal use in case of stolen card.

What are Storage devices?

Storage Devices are the data storage devices that are used in the computers to store the data. The computer has many types of data storage devices. Some of them can be classified as the removable data Storage Devices and the others as the non removable data Storage Devices. 

The memory is of two types; one is the primary memory and the other one is the secondary memory.

The primary memory is the volatile memory and the secondary memory is the non volatile memory. The volatile memory is the kind of the memory that is erasable and the non volatile memory is the one where in the contents cannot be erased. Basically when we talk about the data storage devices it is generally assumed to be the secondary memory.

The secondary memory is used to store the data permanently in the computer. The secondary storage devices are usually as follows: hard disk drives – this is the most common type of storage device that is used in almost all the computer systems. The other ones include the floppy disk drives, the CD ROM, and the DVD ROM. The flash memory, the USB data card etc.

 

 

Storage device

Alternatively referred to as storage, storage media, or storage medium, a storage device is a hardware device capable of holding information. There are two storage devices used in computers; a primary storage device such as computer RAM and a secondary storage device such as a computer hard drive. The secondary storage could be a removable, internal, or external storage. In the picture to the right, is an example of a Drobo, an external secondary storage device. Without a storage device, you and your computer would not be able to save any settings or information and would be considered a dumb terminal. Below, are some additional examples of storage devices that are used with computers:

• Floppy diskette
• CD-ROM disc
• CD-R and CD-RW disc
• Cloud storage
• DVD-R, DVD+R, DVD-RW, and DVD+RW disc
• Jump drive and USB flash drive
• Hard drive
• LS-120
• Tape cassette
• Zip diskette

When saving anything on the computer, you will be asked for the storage location, which is where you want to save the information. By default most of the information you save will be saved to your computer hard drive, however, if you want to move the information to another computer you would want to save it to a removable storage device such as a Jump drive.

 

 

Parity bit

A parity bit is a single bit added to a binary data transmission used to indicate if whether the 0's and 1's within that data transmission is an even or odd number. The parity bit is used in parity error checking to find errors that may occur during data transmission. In the picture to the right, is an example of a 8-bit binary number with the ninth digit being the parity bit.

A parity bit, or check bit, is a bit added to the end of a string of binary code that indicates whether the number of bits in the string with the value one is even or odd. Parity bits are used as the simplest form of error detecting code.

There are two variants of parity bits: even parity bit and odd parity bit. In case of even parity, the parity bit is set to 1, if the number of ones in a given set of bits (not including the parity bit) is odd, making the number of ones in the entire set of bits (including the parity bit) even. If the number of ones in a given set of bits is already even, it is set to a 0. When using odd parity, the parity bit is set to 1 if the number of ones in a given set of bits (not including the parity bit) is even, keeping the number of ones in the entire set of bits (including the parity bit) odd. when the number of set bits is odd, then the odd parity bit is set to 0.

Functional units of a computer

What are the main functional units of a computer? Describe the functions of each unit.

A computer can process data, pictures, sound and graphics. They can solve highly complicated problems quickly and accurately. These multidimensional functions of a computer are executed by a logical and orderly combination of some functional units described as follows:

 

 Fig: Block Diagram of Computer showing the major functional units 

 

1. Input Unit:

Computers need to receive data and instruction in order to solve any problem. Therefore we need to input the data and instructions into the computers. The input unit consists of one or more input devices. Keyboard is the one of the most commonly used input device. Other commonly used input devices are the mouse, floppy disk drive, magnetic tape, etc. All the input devices perform the following functions:

§  Accept the data and instructions from the outside world.

§  Convert it to a form that the computer can understand.

§  Supply the converted data to the computer system for further processing.

2. Processing Unit: This is the responsible for processing all the various operations that goes on in the system unit. It is referred to as the brain of the computer system, without it the computer will be valueless. Example of processing unit is the central processing unit (CPU).

The CPU is like brain performs the following functions:

§  It performs all calculations

§  It takes all decisions

§  It controls all units of the computer
 

The processing unit can be divided into three sections:

i. Memory/Storage Unit

ii. Control Unit

iii. Arithmetic and logical unit (ALU)

The Memory/Storage Unit: The storage unit of the computer holds data and instructions that are entered through the input unit, before they are processed. It preserves the intermediate and final results before these are sent to the output devices. It also saves the data for the later use. The various storage devices of a computer system are divided into two categories.

§  Primary Storage: Stores and provides very fast. This memory is generally used to hold the program being currently executed in the computer, the data being received from the input unit, the intermediate and final results of the program. The primary memory is temporary in nature. The data is lost, when the computer is switched off. In order to store the data permanently, the data has to be transferred to the secondary memory.
The cost of the primary storage is more compared to the secondary storage. Therefore most computers have limited primary storage capacity.

§  Secondary Storage: Secondary storage is used like an archive. It stores several programs, documents, data bases etc. The programs that you run on the computer are first transferred to the primary memory before it is actually run. Whenever the results are saved, again they get stored in the secondary memory. The secondary memory is slower and cheaper than the primary memory. Some of the commonly used secondary memory devices are Hard disk, CD, etc.,

The Control Unit: It controls all other units in the computer. The control unit instructs the input unit, where to store the data after receiving it from the user. It controls the flow of data and instructions from the storage unit to ALU. It also controls the flow of results from the ALU to the storage unit. The control unit is generally referred as the central nervous system of the computer that control and synchronizes its working.

Functions of the control unit:

• It carries out many tasks such as decoding, fetching, handling the execution and finally storing the results.
• It controls the execution of instructions in a sequential order.
• It guides the flow of data through the different parts of the computer.
• It interprets the instructions.
• It regulates the time controls of the processor.
• It sends and receives control signals from various peripheral devices.

The Arithmetic and Logical Unit (ALU): This unit is responsible for performing all the various Arithmetic operation of addition, subtraction, multiplication, division and relational operations Such as not equal to (≠), greater than (>), less than (< ), greater than or equal to (≥) and logical operations Etc. Whenever calculations are required, the control unit transfers the data from storage unit to ALU once the computations are done, the results are transferred to the storage unit by the control unit and then it is send to the output unit for displaying results.

Main Functions:

§  All calculations are performed in the Arithmetic Logic Unit (ALU) of the computer.

§  It also does comparison and takes decision.

3. Output Unit: The output unit of a computer provides the information and results of a computation to outside world. Printers, Visual Display Unit (VDU) are the commonly used output devices. Other commonly used output devices are floppy disk drive, hard disk drive, and magnetic tape drive.