C1 introduction to computers, Study notes of Computer science

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Introduction to Computers

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Contents

• 1. Definition of Computers
• 2. History of Computers
• 3. Classification of Computers.................................................................................
• 4. Components of the Computer Systems
• 5. Basic Organisation of a Computer
• 6. Number System
• 7. Miscellaneous

Comparison Between Computer with Calculator

S. No. Characteristics (^) Calculator Computer

1. Speed Fast Much Fast
2. Performance

Simple Calculation and numeric processing

Complex problem and non- numeric processing also

3. Memory

Less internal memory, no permanent storage, temporary storage only

Large internal memory and large permanent storage available

4. Machine Electronic Device Electronic Device
5. Operation Arithmetic Arithmetic and logical

2. History of Computers

Charles Babbage is the father of computer, because the parts and working principle of the Analytical Engine, which is invented by him is similar to today‘s computer.

Evolution of Computer

• Abacus
• Astrolabe
• Pascaline
• Stepped Reckoner
• Difference Engine
• Analytical Engine
• Punch Cards
• ENIAC (Electrical Numerical Integrator and Calculator)
• Von Neumann Machine

Generations of Computers with Features The computer can be classified into four generations according to their type of electronic

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devices such as Vacuum Tube, Transistor, IC etc. The First Generation Computers (1949-55)

Main Features: The computers of this generation used vacuum tubes. These computers used machine language for giving instructions. They used the concept of stored program. These computers were 5000 times faster than the MARK-I. The first generation computers were welcomed by Government and Universities.

Limitations: These computers were very big in size. The ENIAC machine (Electronic Numerical Integrator and Calculator) was 30 x 50 feet in size and 30 tons in weight. So, these machines required very large space for their workings. Their power consumption was very high. These computers had slow operating speed and small computing capacity. These computers had a very small memory.

The Second Generation Computers (1956-65)

Main Features: The computers of this generation replaced vacuum tubes with transistors. Magnetic cores were invented for storage. Different magnetic storage devices were developed in this generation. Commercial applications were developed during this period. Eighty present of these computers were used in business and industries.

Third Generation Computers (1966-75)

Main Features: The third generation computers replaced transistors with ‗Integrated Circuits‘. These Integrated Circuits are also known as chips. The size of main memory was increased and reached about 4 megabytes. Magnetic disk technology had been improved and drive having capacity up to 100 MBPS came into existence.

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Languages Used in Computer Generations

Generations Languages used First Generation Machine Language Second Generation Assemble Language, Mnemonics

Third Generation High Level Language, BASIC, PASCAL, COBOL, FORTRON Fourth Generation 4 th^ Generation Languages Fifth Generation Artificial Intelligence

Expand COBOL, BASIC, FORTRON and IBM

• COBOL – Common Business Oriented Language
• BASIC - Beginner‘s All Purpose Symbolic Instruction Code
• FORTRON – Formula Translation
• IBM – International Business Machine

Expand IC, SSI, MSI, LSI, and VLSI

• IC – Integrated Circuit.
• SSI - Small Scale Integration.
• MSI - Medium Scale Integration.
• LSI - Large Scale Integration.
• VLSI - Very Large Scale Integration.

3. Classification of Computers

Based on physical size, performance and application areas, we can generally divide computers into seven major categories:

1. Personal Computer
2. Portable Computers
3. Workstations
4. Micro Computer
5. Mini Computer
6. Mainframe Computer, and
7. Super Computer

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Personal Computers A Personal Computer (PC) is a self-contained computer capable of input, processing, output, and storage. A personal computer is designed to be a single-user computer and must have at least one input device, one output device, a processor, and memory. The three major groups of PCs are Desktop Computers, Portable Computers, and Handheld Computers. Let‘s describe one type of Personal Computers,

Desktop Computers: A desktop computer is a PC designed to allow the system unit, input devices, output devices, and other connected devices to fit on top of, beside, or under a user‘s desk or table. This type of computer may be used in the home, a home office, a library, or a corporate setting.

Features:

• A small, relatively inexpensive computer designed for an individual user.
• In price, personal computers range anywhere from a few hundred dollars to thousands of dollars.
• All are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Example:
• Businesses use personal computers for word processing, accounting, desktop publishing, and for running Spreadsheet and database management applications.
• At home, the most popular use for personal computers is for playing games.

Portable Computers A portable computer is a PC small enough to be moved around easily. As the name suggests, a laptop computer fits comfortably on the lap. As laptop computers have decreased in size, this type of computer is now more commonly referred to as a notebook computer. Manufacturers recently began introducing a new type of computer called the tablet PC, which has a Liquid Crystal Display (LCD) screen on which the user can write using a special-purpose pen, or stylus. Tablet PCs rely on digital ink technology that allows the user to write on the screen. Another type of portable computer, called a Wearable Computer, is worn somewhere on the body, thereby providing a user with access to mobile computing capabilities and information via the Internet.

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Analog and Digital Computers Based on type of operations, computers can be classified into Analog and Digital computers. The major differences are highlighted in following table, S. No. Analog Computers Digital Computers

1. Process measured data Process discrete data
2. Analog computers are not precise

Digital computers are more precise

3. Processing speed is low Processing speed is high
4. Less accuracy More accuracy Hybrid Computer A computer which is capable of inputting and outputting in both Digital and Anlog signals. In other words, it is combination of Analog and Digital computers.

Mainframe Computer Mainframes are computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial processing.

These computers are larger, more powerful, and more expensive than midrange servers; a mainframe computer is capable of accommodating hundreds of network users performing different computing tasks. These computers are useful for dealing with large, ever- changing collections of data that can be accessed by many users simultaneously. Government agencies, banks, universities, and insurance companies use mainframes to handle millions of transactions each day.

Super Computer The fastest type of computer. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations.

For example, weather forecasting requires a supercomputer. Other uses of supercomputers include animated graphics, fluid dynamic calculations, nuclear energy research, and petroleum exploration.

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4. Components of the Computer Systems

Basic components of the computer system are: Input Unit Output Unit Central Processing Unit Memory Unit

Input Units An input device is a device that is used to input data or information into a computer. Some examples of input devices include:

Keyboard: It is a text base input device that allows the user to input alphabets, numbers and other characters. It consists of a set of keys mounted on a board.

Alphanumeric Keypad - It consists of keys for English alphabets, 0 to 9 numbers, and special characters like + − / * ( ) etc. Function Keys - There are twelve function keys labelled F1, F2, F3… F12. The functions assigned to these keys differ from one software package to another. These keys are also user programmable keys. Special-function Keys - These keys have special functions assigned to them and can be used only for those specific purposes. Functions of some of the important keys are defined below. o Enter - It is similar to the ‗return‘ key of the typewriter and is used to execute a command or program. o Spacebar - It is used to enter a space at the current cursor location. o Backspace - This key is used to move the cursor one position to the left and also delete the character in that position. o Delete - It is used to delete the character at the cursor position. o Insert - Insert key is used to toggle between insert and overwrite mode during data entry. o Shift - This key is used to type capital letters when pressed along with an alphabet key. Also used to type the special characters located on the upper-side of a key that has two characters defined on the same key. o Caps Lock - Cap Lock is used to toggle between the capital lock features. When ‗on‘, it locks the alphanumeric keypad for capital letters input only.

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Scanner: Scanner is an input device used for direct data entry from the source document into the computer system. It converts the document image into digital form so that it can be fed into the computer. Capturing information like this reduces the possibility of errors typically experienced during large data entry. Hand-held scanners are commonly seen in big stores to scan codes and price information for each of the items. They are also termed the bar code readers.

Bar Codes: A bar code is a set of lines of different thicknesses that represent a number. Bar Code Readers are used to input data from bar codes. Most products in shops have bar codes on them. Bar code readers work by shining a beam of light on the lines that make up the bar code and detecting the amount of light that is reflected back

Light Pen: It is a pen shaped device used to select objects on a display screen. It is quite like the mouse (in its functionality) but uses a light pen to move the pointer and select any object on the screen by pointing to the object. Users of Computer Aided Design (CAD) applications commonly use the light pens to directly draw on screen.

Digital camera: A digital camera can store many more pictures than an ordinary camera. Pictures taken using a digital camera are stored inside its memory and can be transferred to a computer by connecting the camera to it. A digital camera takes pictures by converting the light passing through the lens at the front into a digital image.

The Speech Input Device: The ―Microphones - Speech Recognition‖ is a speech Input device. To operate it we require using a microphone to talk to the computer. Also we need to add a sound card to the computer. The Sound card digitizes audio input into 0/1s.A speech recognition program can process the input and convert it into machine-recognized commands or input.

Touch Screen: It allows the user to operate/make selections by simply touching the display screen. Common examples of touch screen include information Kiosks, and bank ATMs.

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Output Units

In computers, a unit which delivers information from the computer to an external device or from internal storage to external storage.

Monitor: Monitor is an output device that resembles the television screen and uses a Cathode Ray Tube (CRT) to display information. The monitor is associated with a keyboard for manual input of characters and displays the information as it is keyed in. It also displays the program or application output. Like the television, monitors are also available in different sizes.

Liquid Crystal Display (LCD): LCD was introduced in the 1970s and is now applied to display terminals also. Its advantages like low energy consumption, smaller and lighter have paved its way for usage in portable computers (laptops).

Printer: Printers are used to produce paper (commonly known as hardcopy) output. Based on the technology used, they can be classified as Impact or Non-impact printers. Impact printers use the typewriting printing mechanism wherein a hammer strikes the paper through a ribbon in order to produce output. Dot-matrix and Character printers fall under this category. Non-impact printers do not touch the paper while printing. They use chemical, heat or electrical signals to etch the symbols on paper.

Inkjet, Deskjet, Laser, Thermal printers fall under this category of printers - When we talk about printers we refer to two basic qualities associated with printers: resolution, and speed. Print resolution is measured in terms of number of dots per inch (dpi). Print speed is measured in terms of number of characters printed in a unit of time and is represented as characters-per-second (cps), lines-per-minute (lpm), or pages- per-minute (ppm).

Plotter - Plotters are used to print graphical output on paper. It interprets computer commands and makes line drawings on paper using multi-coloured automated pens. It is capable of producing graphs, drawings, charts, maps etc. Computer Aided Engineering (CAE) applications like CAD (Computer Aided Design) and CAM (Computer Aided Manufacturing) are typical usage areas for plotters.

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the hard drive, optical storage devices such as CD-ROMs and DVD-ROMs, as well as read- only memories.

Technical Characteristics: a) Capacity, representing the global volume of information (in bits) that the memory can store b) Access Time, corresponding to the time interval between the read/write request and the availability of the data c) Cycle Time, representing the minimum time interval between two successive accesses d) Throughput, which defines the volume of information exchanged per unit of time, expressed in bits per second e) Non-volatility, which characterizes the ability of a memory to store data when it is not being supplied with electricity

The ideal memory has a large capacity with restricted access time and cycle time, a high throughput and is non-volatile.

However, fast memories are also the most expensive. This is why memories that use different technologies are used in a computer, interfaced with each other, and organised hierarchically.

The fastest memories are located in small numbers close to the processor. Auxiliary memories, which are not as fast, are used to store information permanently.

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Memory can also be classified as, Primary Memory Secondary Memory

Primary Memory: The primary memory or the main memory is part of the main computer system. The processor or the CPU directly stores and retrieves information from it. This memory is accessed by CPU, in random fashion. That means any location of this memory can be accessed by the CPU to either read information from it, or to store information in it.

Primary memory stores and provides very fast access. 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.

• 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.

Types of Primary Memory

RAM is RWM (Read Write Memory) - Random access memory, generally called RAM is the system's main memory, i.e. it is a space that allows you to temporarily store data when a program is running.

Unlike data storage on an auxiliary memory such as a hard drive, RAM is volatile, meaning

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• 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.,

Secondary Storage Devices - Secondary storage devices, as indicated by the name, save data after it has been saved by the primary storage device, usually referred to as RAM (Random Access Memory). From the moment we start typing a letter in Microsoft Word, for example, and until we click on "Save," your entire work is stored in RAM. However, once you power off your machine, that work is completely erased, and the only copy remaining is on the secondary storage device where we saved it, such as internal or external hard disk drive, optical drives for CDs or DVDs, or USB flash drive.

Internal Hard Disk Drive - The internal hard disk drive is the main secondary storage device that stores all of your data magnetically, including operating system files and folders, documents, music and video. The hard disk drive is a stack of disks mounted one on top of the other and placed in a sturdy case. They are spinning at high speeds to provide easy and fast access to stored data anywhere on a disk.

External Hard Disk Drive - External hard disk drives are used when the internal drive does not have any free space and you need to store more data. In addition, it is recommended to always back up all of our data and an external hard drive can be very useful, as they can safely store large amounts of information. They can be connected by either USB connection to a computer and can even be connected with each other in case you need several additional hard drives at the same time.

Optical Drive - An optical drive uses lasers to store and read data on CDs and DVDs. It basically burns a series of bumps and dips on a disc, which are associated with ones and zeros. Then, this same drive can interpret the series of ones and zeros into data that can be displayed on your monitors. There are a few different types of both CD and DVD disks, but the main two types include R and RW, which stand for Recordable (but you can write information on it just once) and Rewritable (meaning you can record data on it over and over again).

USB Flash Drive - Flash memory is a compromise between RAM-type memories and ROM memories. Flash memory possesses the non-volatility of ROM memories while providing

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both read and writes access. However, the access times of flash memories are longer than the access times of RAM.

Memory Size All digital computers use the binary system, i.e. 0‘s and 1‘s. Each character or a number is represented by an 8 bit code. The set of 8 bits is called a byte. A character occupies 1 byte space. A numeric occupies 2 byte space. Byte is the space occupied in the memory. The size of the primary storage is specified in KB (Kilobytes) or MB (Megabyte). One KB is equal to 1024 bytes and one MB is equal to 1000 KB. The size of the primary storage in a typical PC usually starts at 16 MB. PCs having 32 MB, 48 MB, 128 MB, 256 MB memory are quite common.

Volatile and Non-Volatile Memory

• Volatile Memory: Also known as volatile storage is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply. It has been less popularly known as temporary memory.
• Non-Volatile Memory: Non-volatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. Examples of Non-Volatile Memory:
• Read-only memory
• Flash memory
• Most types of magnetic computer storage devices (e.g. hard / floppy disks &magnetic tape)
• Optical discs
• Early computer storage methods such as paper tape and punch cards.

Non-volatile memory is for long-term persistent storage. The most widely used form of primary storage today is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost.

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