Memory : Memory Memory is a place in computer where the data, commands and the results after processing are stored. It may be considered like a spread sheet which have rows and columns. The intersection of row and column makes a cell. Each cell has its own number which is called address of memory location.
Types of Memory : Types of Memory Memory
Primary Memory Secondary Memory
RAM ROM Floppy, CD, DVD,
DRAM PROM Pen Drive &
SRAM EPROM Hard Disc etc
SDRAM EEPROM
Primary Memory : Primary Memory It is also called Internal Memory, Main Memory or IAS (Immediate Access Storage). It is a part of CPU & works like human memory, the stored data can be retrieved as & when required. Programs & instructions are stored in it to make work it automatically. It is very costly so it is used in limited capacity of storage. Main memory stores:
Instructions to be obeyed by other components of CPU.
Instructions currently being obeyed.
Instructions awaiting to be obeyed.
Data awaiting for processing.
Data currently being processed.
Processed data awaiting for output.
Primary memory is contained in two types of chips:
a) RAM (Random Access Memory)
b) ROM (Read Only Memory)
RAM (Random Access Memory) : RAM (Random Access Memory) It is a short term volatile memory which holds information needed for a particular task. New information can be recorded, read & erased. So it is also called read & write memory. RAM forgets every thing as the computer is switched off. Random access memory means that CPU can find each part of the memory straight away because each part of memory is numbered (address of memory location). It is of three types:-
DRAM (Dynamic RAM)
SRAM (Static RAM)
SDRAM (Synchronous Dynamic RAM)
Slide 5 : DRAM: The word dynamic means that this memory needs to be refreshed continuously. To refresh it the power is supplied thousands times per second otherwise it will loose its data.
SRAM: It is more faster & lesser volatile than DRAM. It is costly & more power is required. The word static means that the refreshing in SRAM is not required as frequently as in DRAM.
SDRAM: It is very much like a DRAM which works on high clock rate speed.
ROM (Read Only Memory) : ROM (Read Only Memory) It holds sets of program which tell processor what to do, e.g. how to recognize keys, which key is to be processed & how to light up the screen. It checks memory & operating system. These programs are burnt in ROM at the time of manufacturing. So it is also called firmware. The programs in ROM cannot be changed. Some variations of ROM are:
PROM (Programmable Read only Memory)
EPROM (Erasable Programmable ROM)
EEPROM (Electrically Erasable Programmable ROM)
Slide 7 : PROM: Original program in ROM can slightly be altered by using special instruments.
EPROM: The instructions/programs can be erased with the help of Ultra Violet Light & then programmed again. For this purpose the ROM chip needs to be removed from the motherboard.
EEPROM: The instructions/programs can be erased electrically & then programmed. For this purpose there is no need to remove the ROM chip from the motherboard.
Secondary Memory : Secondary Memory It is also called auxiliary memory, backing storage devices & external memory. It holds mass of information that may be transferred to CPU as and when required.
It is much cheaper than primary memory
Larger Capacity
Less speed
Portable
e.g. Hard Disc, Compact Disc, Floppy Disc & Pen Drive
Measuring Unit of Memory : Measuring Unit of Memory Bit is the smallest measuring unit of Memory. The word bit is derived from combination of Binary + Digit.
Here 0 is 1 Bit & 1 is 1 Another Bit.
4 Bit = 1 Nibble
8 Bit = 1 Byte
1024 Bytes = 1 Kilo Byte (KB)
1024 Kilo Byte = 1 Mega Byte (MB)1024 Mega Byte = 1 Giga Byte (GB)
1024 Giga Byte = 1 Terra Byte (TB)
Secondary Memory Devices or Backing Storage Devices : Secondary Memory Devices or Backing Storage Devices Floppy Disc: It is a magnetic storage media, using flat circular platter. In it a magnetic disc is covered by a plastic cover. The magnetic disc is divided into tracks & sectors. The magnetic head is used to read & write data on it.
Non reliable.
Less Cost.
Available in 3.5 inches to 5.25 inches size.
Storage capacity may be 1.44 MB.
Slide 11 : Compact Disc (CD): Laser beams are used to read & write data. It is also called optical disc. It is most popular optical storage media & available in two types :
CD/R = CD Readable
CD/RW = CD Rewriteable
The storage capacity of CD is 550 MB to 760 MB.
LASER : Light Amplification of Stimulated Emissions of Rays.
Slide 12 : Digital Versatile Disc (DVD): A special technique is used to store data in it. The storage capacity of DVD is 6 time greater than CD. It is available in storage capacity of 4.17 GB.
Pen Drive:
A New secondary storage device with USB Features.
At present very popular media.
Easy to store, read & carry.
Storage capacity varies from 2 GB to 40 GB.
Slide 13 : Hard Disc: It is permanently fixed in CPU. In it many magnetic discs are packed in a metal box. Both sides of magnetic disc are used to store data. To store & read data magnetic heads are used. Available in 40, 80, 120 or 160 GB storage capacity. Its speed is measured in RPM (Rotation Per Minute).
Speed may be 3600 or 7200 RPM depending upon the quality of Hard disc.
Input Devices : Input Devices Microphone
Mouse
Keyboard
Optical Scanner
OCR (Optical Character Recognition)
BCR (Bar Code Reader)
OMR (Optical Mark Reader)
MICR (Magnetic Ink Character Reader)
Light Pen
Touch Screen
Track Ball
Joy Stick & A Wheel
Microphone : Microphone It is an input device. In it inputs are given to the CPU as voice. We can use it with VRS (Voice Recognition System) where we dictate & computer types that automatically. In this system there are more possibilities of mistakes than keyboard typing. It is of two types:
Hand Held Microphone.
Desktop Microphone.
Mouse : Mouse It is a pointing device used in GUI based operating systems. It is used to:
Select Menus & Commands.
Move & open the icons.
Resize windows.
Start or Close a program/application.
Choose options.
Mainly there are three types of mouse:
Scroll Mouse
Optical Mouse
Wireless Mouse
Slide 17 : Scroll Mouse: It has a magnetic ball in its base. The movement of that ball controls the movement of pointer on the screen or a particular window.
Optical Mouse: In it the movement of pointer is controlled by laser lights & small sensors.
Wireless: In it there is no need of wire to connect it with CPU. Its working is just like a remote control. A signal receiver is attached with CPU, that receives the signals from the mouse and controls the pointer.
Keyboard : Keyboard It is a flat piece of plastic board which holds small buttons on it. These buttons are called keys. Normally, there are 104 keys on a standard keyboard. Keys may be divided as following:
Alphabetic Keys (A to Z) or (a to z)
Numeric Keys (0 to 9)
Function Keys (F1 to F12)
Lock Keys ( Caps Lock, Num Lock & Scroll Lock)
Special Keys (Enter, Ctrl, Esc, Del, Insert & Backspace)
Key Symbol (Tab, Shift, Print Screen & Pause)
Cursor Movement Keys or Arrows Keys.
Slide 19 : There are three types of keyboards:
Alphanumeric Keyboard.
Multimedia Keyboard.
Wireless Keyboard.
Slide 20 : Optical Scanner: These devices are used for automatic data input. The devices of this category completely eliminate manual input data.
OCR (Optical Character Recognition): It is an example of optical scanner. Mainly used in Banks to convert the scanned image of a typed or printed page into text that can be edited on the computer.
BCR (Bar Code Reader): It is actually a special type of image scanner. It translates printed images into an electronic format (0 & 1) that can be stored in a computer’s memory. It also can be altered with the help of right kind of software.
Bar Code : Bar Code Special identification code that consists of a set of vertical lines and spaces of different widths
It is used for fast identification of items like books, badges, postal packages etc.
Universal Product .
Slide 22 : OMR (Optical Mark Reader): It is used for checking documents and question papers. OMR directs thin beam of light on the surface of the paper. Lesser amount of light is transmitted through dots as compared to nearby surface due to which answer is recognized by computer.
Can read 10,000 documents per hour.
Results on the same day.
No favoritism or mistake.
Slide 23 : MICR (Magnetic Ink Character Reader): In it a special ink is used which contains magnetic particles of iron oxide. The characters are printed in different styles. These characters can be recognized by the reader from the shape of the wave form of the electronic pulse induced in the magnetism. Its reading speed is 24000 documents per minute. Mainly used in banks for cheques & DDs.
Slide 24 : Light Pen: It is an input device that allows user to write on or point at a special pad or the screen of pen-based computer, such as a PDA.
Touch Screen: Touch screen or touch panel display are an alternative of keyboard. Here input can be given through computer screen. Users touch electronic buttons displayed on the screen or they may use light pen.
Track Ball: It is a pointing device. In it there are three buttons which works as mouse button. The movement of pointer is controlled by a Ball. It takes lesser space than a mouse and can be used on any type of surface. Mainly used in portable computers.
Slide 25 : Joystick & a wheel: It is a pointing device commonly used in games, CAD & CAM. The movement of pointer is controlled with the help of lever which can move in all sides. It provides more realistic control than a mouse or a keyboard for many games. The joystick attached with computer through a cable connected to the game port.
CAD: Computer Aided Designing.
CAM: Computer Aided Manufacturing.
Output Devices : Output Devices Monitor: Of all the devices, monitor is perhaps the most important, because it is the output device that user interact with most intensively. Computer information is displayed visually with a video adapter card and monitor. Information is processed within the CPU that needs to be visually displayed is sent to video adapter. The video adapter converts information from binary to human understandable form. Two basic types of monitors are used with microcomputers or PCs.
C.R.T. (Cathode Rays Tube): It is used with desktop computers and looks/works like a typical television screen. This type uses a large vacuum tube, called CRT.
L.C.D. (Liquid Crystal Display): It is also called flat panel monitor, & commonly used with notebook computers. Most of these employ liquid crystal display to render images.
Either of above types can be monochrome monitor, displaying one color against a contrasting background, or color monitor displaying more than 65000 colors depends on the quality. Any color may be obtained by mixing the three primary colors Red, Green, Blue i.e. RGB
Slide 27 : Resolution: The mode of dividing screen into small square grid areas for visual display is known as resolution. One square area is meant for displaying one dot. A group of several dots makes up a pixels. Every character is made up of several pixels. The quality of monitor depends on the resolution. High resolution means high quality of monitor. VDU has separate storage of about 1 KB. Most of the monitors are:
800 x 600 Pixels
1024 x 768 Pixels
1280 x 1024 Pixels resolutions.
Printer : Printer After a document is created on the computer, it can be sent to a printer for a “hard copy” (printout). Some printer offer special features such as colored and large page formats. Some of the most commonly used printers are:
Laser Printer: A laser printer produces high quality print that one normally finds in publishing. It is extremely fast and quiet. Moreover, the operation of a laser printer is easy with automatic paper loading and no smudging or messing up of ink ribbons. Most laser printers output 6 to 12 pages per minute. Minimum buffer memory in a laser printer is 1 MB. It is a non-impact printer.
Slide 29 : Dot Matrix Printer (DMP): The DMP is a versatile and inexpensive output device and is suitable for most of our printing jobs. In a DMP, the print head physically “hits” (Impacts) the paper through the ribbon and produces text (or image) by combinations of dots; hence the name dot matrix printer. Its speed is measured in CPS (Characters Per second). Although DMP is less expensive, but is louder, slower and produces lower quality than a laser printer. It is an impact printer.
Slide 30 : Inkjet Printer: An inkjet printer creates an image directly on paper by spraying ink through as many as 64 tiny nozzles. Although the image it produces is not generally quite as sharp as the output of a laser printer, the quality of ink-jet images is still high.
In general, ink-jet printer offers printing quality lying between Dot-Matrix and laser printer, providing print resolution of around 360 or more dots per inch. Like laser printer, an ink-jet printer is quiet and convenient, but not particularly fast. Typically, an ink-jet printer is more expensive than a dot-matrix printer, but costs only half as much as a laser printer.
Slide 31 : Printers may also be classified as:
Character Printer. (e.g. Dot Matrix Printer)
Line Printer.
Page Printer. (e.g. Laser Printer & works like a Photocopier)
Slide 32 : Line Printer: A line printer is generally used with large computer systems to produce data processing reports for use within the organization. Line printers are high speed printers with speeds ranging anywhere from 100 to about 3800 lines per minutes. In the past, print quality on line printers was not high. Developments in technology are improving the print quality on line printer. Minimum cost of a line printer is about Rs. One Lac.
Plotter : Plotter A plotter is a special kind of output device, that like a printer, produces images on paper, but does so in a different way. Plotters are designed to produce large drawings or image, such as construction plans for buildings or blueprints for mechanical objects.
An array of different colored pens in a clip rack and a robotic arm to draw with colored pens. Plotter receives the instructions from the computer & picks up appropriate pen through its arm, draw the images according to information. Mainly plotters are two types:
Flat Bed Type: Its size is small & can be put on a table.
Drum Type: These plotters have very big size & a big size of paper can be used in it.
Speaker : Speaker Speaker is an output device which converts electric energy into sound energy. Mainly used to hear music, any type of voice & conversations of people with each other etc. Speakers may be of following types:
Stereo Headphones.
Desktop Stereo Speakers.
Laptop Mono Speakers.
Laptop Stereo Speakers.
Monitor Stereo Speakers.
Monitor Stand Speakers.
Monitor Mounted Speakers.
Keyboard stereo Speakers.
Quadraphonic Speakers.
Surround Sound Speakers.
51. Surround Speakers.
7.1 Surround Speakers.
7.1 Wide Configuration Speakers.