Chapter No 4 Secondary Storage Devices Magnetic Storage

Chapter No. 4 Secondary Storage Devices

Magnetic Storage Devices

Magnetic storage Devices � Magnetic storage devices are the storage of data on a magnetized medium. � Magnetic storage uses different patterns of magnetization in a magnetized material to store data and is a form of non-volatile memory. � The information is accessed using one or more read/write heads. � Hard disks is widely used to store computer data as well as audio and video signals.

Magnetic storage Devices � Following are the examples of magnetic storage devices: ◦ ◦ Hard Disc Floppy Disc Zip Disk Magnetic Tapes

Hard Disc � Hard disks are manufactured in metal and coated with a magnetisable recording medium, similar to the material used in a floppy disk or audio tape. � A hard disk is a higher capacity medium, with up to hundreds of gigabytes. � Hard disks are much faster than floppy disks and can store much larger amounts of data. � They are usually non-removable, but removable hard disks are becoming more common. � They can be both read from and written to, and are the standard medium for storage on computer systems today.

Hard Disc � It is normally supplied as a sealed unit and will often consists of a number of disks (platters) on a common spindle. � A hard disk is made up of Sectors, Tracks and Cylinders.

Hard Disc � Each disk is divided into tracks and sectors. Each sector can store between 256 and 512 bytes. � The tracks are immediately above and below each other. A particular set of such tracks is called a cylinder. • As the spindle turns the platters, the read/write heads move together in and out between the platters. • At any point in time they are all positioned over one particular cylinder

Hard Disc � It is now fairly standard for a pc to have a hard disk of at least 60 GB. When PCs were first used in the 1980 s, the hard disk’s capacity was measured in MB. But modern data and programs take up much more space especially as they are now GUI based. � Hard disks are pretty reliable � However as a standard they are fixed inside the systems unit/computer case. � Portable (removable) units are available though, and tend to be used mostly by laptop owners. � The specification of a hard disk depends not only on its capacity but also Access time to data. This is affected by the rotation Speed of the disk and also the way in which the disk is connected to the motherboard.

Hard Disc � The hard disk and the hard drive are packaged together.

Floppy Disc � A floppy disk is a low capacity disk which may be removed from the computer. � Data may be written to and read from a floppy. A small notch can be used to make the disk read-only. � Those holding a small amount of data (typically 1. 44 Mb) And ‘Super floppies’ known as ZIP disks (typically 100 Mb) � Floppies have come a long way. There was the 8” floppy, and the 5¼” floppy, and then the 3½“ floppy.

Floppy Disc � The present floppy is a 3. 5 inch magnetic disk of flexible material which typically stores 1. 44 MB of data maximum. � The thin plastic circle is enclosed in rigid plastic to protect it. � A metal sliding access shutter opens when the disk is in the drive so that the read/write head can access the disk itself. � Data can be written to and read from a floppy disk. � A write protected Notch can be used to prevent accidental overwriting of data.

Metal Shutter Plastic Jacket Diskette Write Protected Notch Floppy Disc

� They are small lightweight and easy to transport. � Ideal for backups of small amounts of data or for transfer of data from one machine to another. � Floppy Drives are common to most if not all computers. � On the down side, they may be easily misplaced, damaged or stolen. � There is a risk of transferring VIRUSES

Zip Disk � The zip disk comes in different capacities ranging from 100 MB to 750 MB. � Zip disks are relatively inexpensive. The 750 MB version can store the same amount of data as 520 floppy disks. � Physically the zip disk is about 1½ times the size of a floppy. � Zip disks are popular for backing up hard disks and for transferring large files from one computer to another. � The zip disk is portable and the disk itself operates similarly to a hard disk.

Zip Disk � Zip disks require a zip drive. These are not automatically attached to new systems however, they have to be specially ordered. � A zip drive can be external or internal.

Magnetic Tape � Tape is flexible reels of plastic with a magnetic coating. � It may range from ¼” cartridges to large reels. � Magnetic tape requires a special drive of course and access is slow as it is a sequential access devices. � It is an ideal medium for backup however, because it is fast, inexpensive and has a high storage capacity.

Magnetic Tape �The data is stored in tracks that run along the entire length of the tape. Usually there are 9 tracks.

Types of Monitors �There are two kinds of viewing screen used for monitors. ◦ Cathode-Ray Tube (CRT) ◦ Flat-Panel Display

Cathode-Ray Tube (CRT) Monitor � The CRT display is made up of small picture elements called pixels. The smaller the pixels, the better the image clarity or resolution. It takes more than one illuminated pixel to form a whole character, such as the letter ‘e’ in the word help. � A finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes - fixed location on the screen where a standard character can be placed. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically.

Flat-Panel Display Monitor � The flat-panel display refers to a class of video devices that have reduced volume, weight and power requirement in comparison to the CRT. You can hang them on walls or wear them on your wrists. Current uses of flat-panel displays include calculators, video games, monitors, laptop computer, and graphics display.

Categories of flat-panel display � The flat-panel display is divided into two categories − ◦ Emissive Displays − �Emissive displays are devices that convert electrical energy into light. For example, plasma panel and LED (Light. Emitting Diodes). ◦ Non-Emissive Displays − �Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. For example, LCD (Liquid-Crystal Device).

Printers � Printer is an output device, which is used to print information on paper. � There are two types of printers − ◦ Impact Printers ◦ Non-Impact Printers

Impact Printers � Impact printers print the characters by striking them on the ribbon, which is then pressed on the paper. � Characteristics of Impact Printers are the following − ◦ Very low consumable costs ◦ Very noisy ◦ Useful for bulk printing due to low cost ◦ There is physical contact with the paper to produce an image

Types of Impact Printers � These printers are of two types − � Character printers ◦ Dot Matrix Printer(DMP) ◦ Daisy Wheel � Line printers ◦ Drum Printer ◦ Chain Printer

Character Printers � Character printers are the printers which print one character at a time. � These are further divided into two types: ◦ Dot Matrix Printer(DMP) ◦ Daisy Wheel

Dot Matrix Printer � In the market, one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in the form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character which is why it is called Dot Matrix Printer. � Advantages ◦ Inexpensive ◦ Widely Used ◦ Other language characters can be printed � Disadvantages ◦ Slow Speed ◦ Poor Quality

Daisy Wheel Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower) which is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices that require a few letters to be sent here and there with very nice quality. � Advantages � ◦ More reliable than DMP ◦ Better quality ◦ Fonts of character can be easily changed � Disadvantages ◦ Slower than DMP ◦ Noisy ◦ More expensive than DMP

Line Printers � Line printers are the printers which print one line at a time. � These are of two types − ◦ Drum Printer ◦ Chain Printer

Drum Printer This printer is like a drum in shape hence it is called drum printer. The surface of the drum is divided into a number of tracks. Total tracks are equal to the size of the paper, i. e. for a paper width of 132 characters, drum will have 132 tracks. A character set is embossed on the track. Different character sets available in the market are 48 character set, 64 and 96 characters set. One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000 lines per minute. � Advantages ◦ Very high speed � Disadvantages ◦ Very expensive ◦ Characters fonts cannot be changed �

Chain Printer � In this printer, a chain of character sets is used, hence it is called Chain Printer. A standard character set may have 48, 64, or 96 characters. � Advantages ◦ Character fonts can easily be changed. ◦ Different languages can be used with the same printer. � Disadvantages ◦ Noisy

Non-impact Printers � Non-impact printers print the characters without using the ribbon. These printers print a complete page at a time, thus they are also called as Page Printers. � Characteristics of Non-impact Printers ◦ Faster than impact printers ◦ They are not noisy ◦ High quality ◦ Supports many fonts and different character size

Types of Non-Impact Printers � These printers are of two types − ◦ Laser Printers ◦ Inkjet Printers

Laser Printers These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page. � Advantages ◦ Very high speed ◦ Very high quality output ◦ Good graphics quality ◦ Supports many fonts and different character size � Disadvantages ◦ Expensive ◦ Cannot be used to produce multiple copies of a document in a single printing. �

Inkjet Printers Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features. � They make less noise because no hammering is done and these have many styles of printing modes available. Color printing is also possible. Some models of Inkjet printers can produce multiple copies of printing also. � Advantages ◦ High quality printing ◦ More reliable � Disadvantages ◦ Expensive as the cost per page is high ◦ Slow as compared to laser printer �

Plotters � 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. The plotter is either a peripheral component that you add to your computer system or a standalone device with its own internal processor.

Types of Plotters �Following are two types of plotter ◦ Drum Plotter ◦ Flat-Bed Plotter

Drum Plotter � The drum plotter was the first output device for printing graphics. A drum plotter contains a pen, drum, paper, and ink for output. In this drum rotates the pages and pens draw the images on papers. The drum rotates to change the position of the paper. The length of image is limited. It is because of the limited size of the drum.

Flatbed Plotter � A flatbed plotter is used with many CAD programs for designs. In this plotter writing pen move x-axis and yaxis direction to draw the image. The papers remain stationary on the surface of the flatbed plotter. Different types of pens are used to draw a colorful sketch. The size of the images depends on the size of the flatbed plotter.