Computer System

Computer System:

A computer is a machine that are widely used in homes, offices, banks, hospitals, schools, for weather forecasting, satellite launching and at many others places.

Every machine requires instructions for its proper operations. For example, the remote control of your television set at home has some buttons which help to change  channels, adjust volume and other settings. So, we can say that the remote control helps you input instructions. The display you see on the television screen as a result of those instructions is the television set's output. Similarly, computer being a machine, needs some input and output devices for its correct operations or function.

HOW THE COMPUTER WORKS:

A computer is a programmable electronic device that works according to the instructions given by us. It has the ability to accept data, process it and give useful output. We can also say that computer is a machine that follows the IPO (Input-Process-Output) cycle. The input devices are used to give instructions to the computer which are then processed by the CPU (Central Processing Unit). The results of processing are displayed on the output devices. A computer makes use of different types of memory to store data and instructions.

A computer runs on electricity and understands only two states ON and OFF. ON is represented by 1 and OFF is represented by 0. The computer understands the language on only 0's and 1's. It is called the binary language or the machine language.

Block Diagram of a Computer

INPUT DEVICES:

An input device is a hardware or peripheral device takes data and instructions from us and converts them into binary form that the computer can understand. Some of the devices which are used to enter data into the computer are as follows:

1.     Keyboard:
A computer keyboard is an input device that allows a person to enter letters, numbers, and other symbols. Using a keyboard to enter lots of data is called typing. A keyboard can be connected to the computer through a wire or through a wireless connection.

2.     Mouse:
A computer mouse is a handheld hardware input device that controls a cursor in a GUI (graphical user interface) and can move and select text, icons, files, and folders on your computer. A mouse can be a ball mouse, an optical mouse or a wireless mouse.

The ball mouse has a small metal or rubber ball under it. The movement of the mouse causes the ball to move.

The optical mouse uses light beam or light-emitting diode (LED) to detect the motion of the mouse.

A wireless mouse is not attached to the computer through a wire. Instead, the mouse uses some manner of wireless technology, like Bluetooth, infrared radio waves. Usually, a USB receiver is plugged into the computer and receives signals from the wireless mouse. A wireless mouse is more expensive than an optical or a ball mouse.

3. Scanner:
A scanner is a device that is used for creating a digital copy of the printed images or documents. The digital copy can be edited, sent as attachments through emails or saved. There are various types of scanners such as flatbed scanners, sheet-fed scanners, Drum scanners and handheld scanners. The most commonly used is the flatbed scanner.

4.     Joystick:
A joystick is a cursor control device that is  used to change the position of the cursor or any object on the screen. joysticks are popularly used for playing video games.

5.     Light Pen:
A light pen is an input device and is shaped like a pen. It allows the user to point to displayed objects or draw on the screen in a similar way to a touchscreen but with greater positional accuracy.

6.     Microphone:
A microphone is used to input sound into a computer. It helps in recording your voice or other sounds.

7.     Graphic Tablet:
A graphic tablet is an input device. It is used to draw images and pictures on the computer screen and capturing the handwritten signatures of people in a similar way as you draw pictures with a pencil on paper. A graphic tablet consists of a flat surface on which a user can draw using a pen-like drawing device called stylus.

8.     Barcode Reader:
A barcode is device used to capture and read information contained in a barcode. A barcode is a small image of lines and spaces that can be seen on the packets of many products. Barcodes are widely used in supermarkets for recording the sale of items quickly.

9.     Touch Screen:
A touch screen is a touch-sensitive computer display screen that can also act as an input device.Touch screens are easy to use, and are often found in public places such as cell phones, ATM machines, video games and airports.

10. MICR:
MICR stands for Magnetic Ink Character Recognition. An MICR reader is a device used mainly by the banking industry to ease the processing and clearance of cheques and other documents. The MICR line on a cheque contains details such as the branch code and cheque number. They are printed at the bottom using a special magnetic ink.

11. OCR:
OCR stands for Optical Character Recognition. OCR is an input device used to read a printed text. OCR scans the text optically, character by character, converts them into a machine readable code, and stores the text on the system memory.

12. OMR:
OMR stands for Optical Mark Recognition. OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked. It is specially used for checking the answer sheets of examinations having multiple choice questions.

OUTPUT DEVICES:

An output device takes data in the binary form from the computer and converts it into a form that we can read i.e user-readable form. Some of the devices which are used to display the processed result or output are as follows:

1.     Monitor:
A computer monitor is an output device that displays information in pictorial form. It is also known as VDU (Visual Display Unit). The picture on a monitor is made up of thousands of tiny colored dots called pixels or picture elements. The quality and details of a picture depend on the number of pixels that the monitor can display. The higher number of pixels, the better is the quality of the output. There can two types of monitors-

CRT (Cathode Ray Tube):  CRT is the old style monitors that are bulky and heavy.

TFT (Thin Film Transistor): TFT is a liquid crystal display (LCD) technology. All LCD color display such as televisions use TFT technology. TFT monitors are thin and lightweight.

2. Printer:

Printers are output devices which are used to prepare permanent output on paper.  The output of the printer taken on paper is known as hard copy. There can two types of Printers

Impact Printers: An impact printer is a class of printers that functions by making physical contact with an ink ribbon before striking the page.

Examples: Daisy wheel, dot matrix and line printers

Non-impact printer: Non-impact printer prints without making contact with the paper. They are generally quieter and more efficient than their impact counterparts.

Examples: Laser printer and Inkjet printers

3.     Plotter:

A plotter is a special output device used to produce hard copies of large graphs and designs on paper, such as construction maps, engineering drawings, architectural plans and business charts. 

4.     Speaker:

A computer speaker is an output hardware device that connects to a computer to generate sound. The signal used to produce the sound that comes from a computer speaker is created by the computer's sound card.

COMPUTER MEMORY:

A computer memory is just like a human brain. It is used to store data and instructions. Computer Memory are three types:

A. Primary Memory/Main Memory.

B. Secondary Memory.

C. Cache Memory

A. Primary Memory or Main Memory:

Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device.

Characteristics of Main Memory

1. These are semiconductor memories
2. It is known as main memory.
3. Usually volatile memory.
4. Data is lost in case power is switched off.
5. Faster than secondary memories.
6. A computer cannot run without primary memory.

It is divided into two subcategories RAM and ROM.

1. Random Access Memory (RAM):

RAM is a read/write memory. Information can be written into and read from RAM. It is a volatile memory. This means that any interruption in power supply results in loss of data in RAM. It retains the stored information as long as the power is switched on. When a computer starts, it loads the operating system into RAM. The amount of RAM installed in a computer decides the number and size of programs that the system can run simultaneously.

Types of RAM:

1. Dynamic Random Access Memory (DRAM)
2. Static Random Access Memory (SRAM)

2. Read Only Memory (ROM)

This memory uses Metal Oxide Semiconductor Technology. RAM is read-write memory whereas ROM is Read-Only-Memory. This memory is used to store frequently used programs in the system. ROM is a non-volatile memory as it retains the contents even when the power is switched off. In most computers, ROM is used for storing a special piece of software known as BIOS (Basic Input/Output System). It helps in loading the operating system when the computer is switched on.

Types of ROM:

1. Programmable read-only memory (PROM) 
2. Erasable programmable read-only memory (EPROM) 
3. Electrically erasable programmable read-only-memory (EEPROM)

Distinguish between RAM and ROM:

RAM:

1. The full form of RAM is Random Access Memory.
2. It is Volatile or temporary memory.
3. Data gets erased when power supply off.
4. Faster memory.
5. It is used in the normal operations of a computer after starting up and loading the operating system.

ROM:

1. The full form of ROM is Read Only Memory.
2. It is Non Volatile or permanent memory.
3. Data stored permanently.
4. Slow memory.
5. A ROM chip is used primarily in the start-up process of a computer.

B. Secondary Memory or Auxiliary Memory:

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example- Magnetic Disk, Floppy Disk, Hard Disk, Optical Disks, CD-ROM, DVD, etc.

Characteristic of Secondary memory

1. These are magnetic and optical memories
2. It is non-volatile memory which is used for storage of data in a computer.
3. Data is permanently stored even if power is switched off.
4. Computer may run without secondary memory.
5. Slower than primary memories.

Hard Disk:

A hard disk is the main storage device found inside a computer. A hard disk consists spindle that holds one or more disks called platters. The platters are coated with a thin layer of magnetic material and data is written on them with the help of read-write head. A hard disk can store several gigabytes (GBs) of data and is used for storing applications and files for a user.

Compact Disc:

Compact discs are known as optical storage devices. A compact disc can store approximately 700 MB of data. A laser beam is used for storing data on the disc. Compact disc can be of two types-

1. CD-R: CD-R is called recordable CD. Data once recorded on CD-R cannot be erased.
2. CD-RW: CD-RW is called rewritable CD. Data stored on the CD-RW can be erased and new data can be stored in its place.

DVD:

The full form of DVD is Digital Video Disc or Digital Versatile Disc. A DVD is capable of storing six times more data than a CD. Leaser beam is used to store and read the data. A single-sided DVD can store about 4.7 GB of data. DVDs whcore data on both sides can hold over 9 GB of data.

Blu-ray Disc:
The name Blu-ray Disc is derived from the blue-violet laser that is used to read and right this type of disc. A Blu-ray disc can store more data than a DVD. A Blu-ray disc can store 25 GB of data which is five times tha storage capacity of a DVD. It is mainly used for storing very high-quality video files and video games that require large amounts of storage space.

Pen / Flash Drive:

A pen drive is a storage device that is small in size and can be carried easily. It is a USB (Universal Serial Bus) device that can be used to quickely transfer audio, video and data files from the hatd disk of one computer to another. A pen drive uses flash memory. Flash memory is a technology that allows data to be electrically stored, erased and reprogrammed.

DVD:

A memory card is small in size and can store data in digital format. It is used in various electronic devices like mobile phones, digital cameras, mp3 players and many other portable devices.

C. Cache Memory:

Input- Output operations are very slow. CPU speeds are quite high compared to the access time of main memory. Thus the processor performance is limited by the slow speed of the main memory. To speed up fetching of instructions to CPU, a buffer or cache (pronounced as cash) is used. Normal RAM is expensive and is not fast enough to match the speed of CPU. To reduce the processing time, certain computers use costlier and higher speed memory devices to form a buffer or cache. Cache memory is used between CPU and RAM.

Advantages

The advantages of cache memory are as follows:

1. Cache memory is faster than main memory.
2. It consumes less access time as compared to main memory.
3. It stores the program that can be executed within a short period of time.
4. It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows:

1. Cache memory has limited capacity.
2. It is very expensive

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