Computer Helath related issues -Assignment-2
When the human race started doing some trade, it felt a need for a calculating device. The first calculating device, which was used 2000 years ago was called abacus and the improvements in the calculating device in that age were slow. The next change came after about 1600 years. Following this, the changes were frequent and the mechanical desk calculator was developed around 1800 A.D.
In 1833, Prof. Charles Babbage, the father of the computer, developed a machine called analytical engine which was the vase for the modern digital computer.
The electronic digital computers, which were introduced in 1950's, were using vacuum tubes. Following this, the development in the electronic components helped in the developed of digital computers also. The second-generation computers used transistors.
The introduction of integrated circuits (ICs), also know as chips opened the door for the developed of third generation computers. A very large number of circuit elements (transistors, diodes, resistors, etc.,) could be integrated into a very small (less than 5mm square) surface of silicon and hence the name IC. The third generation computers used small-scale integrated circuits (SSI) which contain about 10-20 components. When large-scale integrated circuits (LSI) (around 30,000 components) were developed, the fourth generation computers were produced.
A computer is an electronic device capable of executing instructions, developed based on algorithms stored in its memory, to process data fed to it and produced the required results faster than human beings.
A computer is designed using four basic units. They are
1) Input Unit: Computers need to receive data and instructions in order to solve any problem. Therefore we need to put the data and instructions into the computer. The input unit consists of one or more input device. The keyboard and mouse of a computer are the most commonly used input devices.
2) Central Processing Unit (CPU): It is the main part of a computer system like the heart of a human being. It interprets the instructions in the program and executes one by one. It consists of three major units.
Control Unit: It controls and directs the transfer of program instructions and data between various units.
Arithmetic and Logic Unit (ALU): Arithmetic operations like (+,-,*,^,/), logical operations like (AND, OR, NOT) and relational operations like (<,>,<=,>=) are being carried out in this Unit.
Registers: They are used to store instructions and data for further use.
3) Memory Unit: It is used to store the Programs and data.
4) Output Unit: It is used to print/display the results, which are stored in the memory unit.
Secondary stored devices refer to floppy disks, magnetic disks, magnetic disks, magnetic tapes, hard disks, compact disks etc., which are used to store huge information for future use. The input unit, output unit and secondary storage devices are together know as Peripheral devices.
The block diagram of a computer is shown below
The components of a computer are connected by using buses. A bus is a collection of wire that carry electronic signals from one component to another. There are standard buses such as Industry Standard Architecture (ISA), Extended Industry Standard Architecture (EISA), Micro-Channel Architecture (MCA), and so on. The standard bus permits the user to purchase the components from different vendors and connect them easily.
The various input and output devices have a standard way of connecting to the CPU and Memory. These are called interface standards. Some popular interface standards are the RS-232C and Small Computer System Interconnect (SCSI). The places where the standard interfaces are provided are called ports.
Data in Computers are represented using only two symbols '0' & '1'. These are called " Binary digiTS" (or) "BITS" for short. A set of 8 bits is called a byte and each byte stores one character. 2n Unique strings are represented using n bits only. For example, Using 2 bits we can represent 4=(22) unique strings as 00, 01, 10, 11. ASCII (American Standards Code for Information Interchange) codes are used to represent each character. The ASCII code includes codes for English Letters (Both Capital & Small), decimal digits, 32 special characters and codes for a number of symbols used to control the operation of a computer which are non-printable.
Binary numbers are formed using the positional notation. Powers of 2 are used as weights in the binary number system. A binary number system. A binary number 10111, has a decimal value equal to 1*24+0*23+1*21+1*20=23. A decimal number is converted into an equivalent binary number by dividing the number by 2 and storing the remainder as the least significant bit of the binary number. For example, consider the decimal number 23. Its equivalent binary number is obtained as show below in figure
High valued binary numbers will be represented by a long sequence of 0's and 1's. A more concise representation is using hexadecimal representation. The base of the hexadecimal system is 16 and the symbols used in this system are 0,1,2,4,5,6,7,8,9,A,B,C,D,E,F. Strings of 4 bits have an equivalent hexadecimal value. For example, 6B is represented by 0110 1011 or 110 1011, 3E1 is represented by 0011 1110 0001 or 11 1110 0001 and 5DBE34 is represented by 101 1101 1011 1110 0011 0100. Decimal fractions can also be converted to binary fractions.
Errors may occur while recording and reading data and when data is transmitted from one unit to another unit in a computer Detection of a single error in the code for a character is possible by introducing an extra bit in its code. This bit, know as the parity check bit, is appended to the code. The user can set the parity bit either as even or odd. the user chooses this bit so that the total number of ones ('1') in the new code is even or odd depending upon the selection. If a single byte is incorrectly read or written or transmitted, then the error can be identified using the parity check bit.
The most common input device is the Keyboard. It is used to input letters, numbers, and commands from the user.
Mouse is a small device held in hand and pushed along a flat surface. It can move the cursor in any direction. In a mouse a small ball is kept inside and the ball touches the pad through a hole at the bottom of the mouse. When the mouse is moved, the ball rolls. This movement of the ball is converted into electronic signals and sent to the computer. Mouse is very popular in the modern computers that use Windows and other Graphical User Interface (GUI) applications.
In this method, human readable characters are printed on documents such In this method, human readable characters are printed on documents such as cheque using special magnetic ink. The cheque can be read using a special input unit, which can recognize magnetic ink characters. This method eliminates the need to manually enter data from cheques into a floppy. Besides saving time, this method ensures accuracy of data entry and improves security.
In this method, special pre-printed forms are designed with boxes which can be marked with a dark pencil or ink. Such a document is read by a document reader, which transcribes the marks into electrical pulses which are transmitted to the computer. These documents are applicable in the areas where responses are one out of a small number of alternatives and the volume of data to be processed is large. For example:
The advantage of this method is that information is entered at its source and no further transcription is required.
An optical scanner is a device used to read an image, convert it into a set of 0's and 1's and store it in the computer's memory. The image may be hand-written document, a typed or a printed document or a picture.
In this method, small bars of varying thickness and spacing are printed on packages, books, badges, tags etc., which are read by optical readers and converted to electrical pulses. The patterns of bars are unique an standardized. For example, each grocery product has been given unique 10-digit code and this is represented in bar code form on every container of this product.
A unit, which takes spoken words as its input, and converts them to a form that can be understood by a computer is called a speech input unit. By understanding we mean that the unit can uniquely code (as a sequence of bits) each spoken word, interpret the word and initiate action based on the word.
Monitors provide a visual display of data. It looks like a television. Monitors are of different types and have different display capabilities. These capabilities are determined by a special circuit called the Adapter card. Some popular adapter cards are,
The smallest dot that can be displayed is called a pixel. The number of pixels that can be displayed vertically and horizontally gives the maximum resolution of the monitor. The resolution of the monitor determines the quality of the display. The higher the resolution the better is the quality of the display. Some popular resolution are 800*640 pixels, 1024*768 pixels, 1280*1024 pixels.
Drum Printers: It consists of a cylindrical drum. The characters to be printed are embossed on its surface
Chain Printers: I has a steel band on which the character sets are embossed.
Her a character to be printed is made up of a finite number of dots and so, the print head consists of an array of pins.
Characters to be printed are sent one character at a time from the memory to the printer. The character code is decoded by the printer electronics and activates the appropriate pins in the print head.
Many dot matrix printers are bi-directional. i.e. they print form left to right as well as from right to left on return. This enhances the speed of printing.
The printing speed is around 300 characters per second.
It consists of a print head, which has a number of small hole or nozzles.
Individual holes can be heated very rapidly by an integrated circuit resistor. When the resistor heats up, the ink near it vaporizes and is ejected through the nozzle and makes a dot on paper placed near the head.
A high-resolution inkjet printer has around 50 nozzles within a height of 7mm and can print with a resolution of 300 dots per inch.
Latest inkjet printers have multiple heads, on per color, which allows color printing.
The printing speed is around 120 characters per second.
Apart from printers, the other output devices are given below:
A flip-flop made of electronic semiconductor devices is used to fabricated a memory cell. These memory cells organized as a Random Access Memory (RAM). Each cell has a capability to store one bit of information. A main memory or store of a computer is organized using a large number of cells. Each cell stores a binary digit. A memory cell, which does not loose the bit stored in it when no power is supplied to the cell, is know as a non-volatile cell.
A word is a group of bits, which are stored and retrieved as a unit. A memory system is organized to store a number of words. A Byte consists of 8 bits. A word may store one or more bytes. The storage capacity of a memory is the number of bytes it can store. The address of the location from where a word is to be retrieved or to be stored is entered in a Memory Address Register (MAR). The data retrieved from memory or to be stored in memory are placed in a Memory Data Register (MDR). The time taken to write a word is known as the Write time. The time to retrieve information is called the Access time of the memory.
The time taken to access a word in a memory is independent of the address of the word and hence it is know as a Random Access Memory (RAM). The main memory used to store programs and data in a computer is a RAM. A RAM may be fabricated with permanently stored information, which cannot be erased. Such a memory is called a Read Only Memory (ROM). For more specialized uses, a user can store his won special functions or programs in a ROM. Such ROM's are called Programmable ROM (PROM). A serial access memory is organized by arranging memory cells in a linear sequence. Information is retrieved or stored in such a memory by using a read/write head. Data is presented serially for writing and is retrieved serially during read.
Magnetic surface recording devices commonly used in computers are Hard disks, Floppy disks, CD-ROMs and Magnetic tapes. These devices are known as secondary or auxiliary storage devices. We will see some of these devices below.
In this device, the medium used to record the data is called as floppy disk. It is a flexible circular disk of diameter 3.5 inches made of plastic coated with a magnetic material. This is housed in a square plastic jacket. Each floppy disk can store approximately on million characters. Data recorded on a floppy disk is read and stored in a computer's memory by a device called a floppy disk is read and stored in a computer's memory by a device called a floppy disk drive (FDD). A floppy disk is inserted in a slot of the FDD. The disk is rotated normally at 300 revolutions per minute. A reading head is positioned touching a track. A voltage is induced in a coil wound on the head when a magnetized spot moves below the head. The polarity of the induced voltage when a 0 is read. The voltage sensed by the head coil is amplified, converted to an appropriate signal and stored in computer's memory.
CD-ROM (Compact Disk Read Only Memory) used a laser beam to record and read data along spiral tracks on a 51/4 disk. A disk can store around 650 MB of information. CD-ROMs are normally used to store massive text data. (such as encyclopedias) which is permanently recorded and read many times. Recently CD writers have come in the market. Using a CD writer, lot of information can be written on CD-ROM and stored for future reference.
Unlike a floppy disk that is flexible and removable, the hard disk used in the PC is permanently fixed. The hard disk used in a higher end Pc can have a maximum storage capacity of 17 GB (Giga Byte; 1 GB= 1024 MB = 230 bytes). Now a days, hard disks capacities of 540 MB, 1 GB, 2 GB, 4 GB and 8 GB are quite common. The data transfer rate between the CPU and hard disk is much higher as compared to the between the CPU and the floppy disk drive. The CPU can use the hard disk to load programs and data as well as to store data. The hard disk is a very important Input/Output (I/O) device. The hard disk drive doesn't require any special care other than the requirement that one should operate the PC within a dust-free and cool room (preferably air-conditioned).
In summary, a computer system is organized with a balanced configuration of different types of memories. The main memory (RAM) is used to store program being currently executed by the computer. Disks are used to store large data files and program files. Tapes are serial access memories and used to backup the files form the disk. CD-ROMs are used to store user manuals, large text, audio and video data.
A processing unit in a computer interprets instructions in a program and carries them out. An instruction in general, consists of a part, which specifies the them out. An instruction in general, consist of a part, which specifies the operation to be performed and other parts, which specify the address of operand. In a processor, a strong of bits is used to code operations and another string of n operations in binary so that 2x = n. For example to code 16 operations we need 4 bits, since 24=16.
An instruction consisting of an operation code and operand address or addresses designed for a specific computer is know as a machine language instruction of that computer. Machine language instructions for input/output, data movement, arithmetic, logic and controlling sequence of operations are available in all computers. A computer's processor has storage registers to store operands and results. It also has a register to store the instruction being executed called "Instruction Register" and a register which store the address of the next instruction to be executed called " Program Counter Register".
A sequence of machine language instructions to solve a problem is know as a machine language program. A computer executes a machine language programs in two phases. In the first phase, it reads and stores the program in its memory. After storing the program, it initiates program execution. In this phase, instructions are retrieved from memory one after another and are decoded and executed.
A set of programs associated with the operation of a computer is called software. The electronic circuits used in building the computer that executes the software is known as the hardware of the computer. For example, a TV bought from a shop is hardware; the various entertainment programs transmitted from the TV station are software. An important point to note is, hardware is a one-time expense and is necessary whereas software is a continuing expense and is vital. Computer software may be classified into two broad categories:
It is the set of programs necessary to carry out operations for a specified application.
Example
Programs
To solve a set of equations
To process examination results
To prepare a Pay-Bill for an organization
To prepare Electricity-Bill for each month.
These are general program written for the system, which provide the environment to facilitate writing of Application software. Some of the system programs are given below:
Compiler: It is a translator system program used to translate a High-level language program into a Machine language program.
Assembler: It is another translator program used to translate an Assembly language program into a Machine language program.
Interpreter: It is also a translator system program used to translate a High level language program into a Machine language program, but it translates and executes line by line.
Loader: It is a system program used to store the machine language program into the memory of the computer.
The computers can execute a program written using binary digits only. This type of programs is called machine language programs. Since these programs use only '0's and '1's it will be very difficult for developing programs for complex problem solving. Also it will be very difficult for a person to understand a machine language program written by another person. At present, computer users do not write programs using machine language. Also these programs written for execution in one computer cannot be used on another type of computer. i.e., the programs were machine dependent.
In assembly language mnemonic codes are used to develop program for problem solving. The program given below shows assembly language program to add two numbers A & B.
| Program code | Description |
| READ A ADD B STORE C PRINT C HALT |
It reads the value of A. The value of B is added with A. The result is store in C. The result in 'C' is printed. Stop execution. |
Assembly language is designed mainly to replace each machine code with and understandable mnemonic code. To execute an assembly language program it should first be translates into an equivalent machine language program. Writing and understanding programs in assembly language is easier than that of machine language. The programs written in assembly language are also machine dependent.
High level language are developed to allow application programs, which are machine independent. High level language permits the user to use understandable codes using the language structure. In order to execute a high-level language program, it should be translated into a machine language either using a compiler or interpreter. The high level languages commonly used are FORTRAN (FORmula TRANslation), BASIC (Beginner's All-purpose Symbolic Instruction Code), COBOL (COmmon Business Oriented Language). Recently developed programming language such as Visual Foxpro, Visual Basic (VB), Visual C++ (VC++) are more popular among the software developers. The following program written in BASIC language is to add two given numbers.
| Program Code | Description |
| 10 INPUT A,B 20 LET C=A+B 30 PRINT C 40 END |
To read the value of A&B A&B are added and result is stored in C Print the value of C Stop execution |
Computers available in remote locations can communicate with each other using a telecommunication line. One way of connecting the computers is by using devices called modems. A modem is used to transfer data from one computer to another using the telephone lines. A modem converts the strings of 0s and 1s into electrical signals which can be transferred over the telephone lines. Both the receiving and the transmitting computer have a telephone connection and a modem. An external modem is connected to the computer like a typical input or an output device. An internal modem is fitted into the circuitry related to the CPU and Memory.
Interconnection of computers which are within the same building or nearby locations forms a network of computers and this network is called a Local Area Network (LAN). A LAN permits sharing of data files, computing resources and peripherals. Interconnection of computers located in far away locations using telecommunication system is know as Wide Area Network (WAN).
Intercommunication between computer network is possible now. Computer networks located in different Organizations can communicate with each other through a facility know as Internet. Internet is a world wide computer network, which interconnects computer networks across countries. The Internet facility know as Internet. Internet is a world wide computer network, which interconnects computer networks across countries. The Internet facilitates electronic mail (email), file-transfer between any two computers and remote access to a computer connected in the internet. This intercommunication facility has changed the style of functioning of the business organization and it has made the world a global village.
