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Secondary storage devices are required mainly because primary storage devices are volatile and information is lost the moment power is switched off. Floppy Disks and Drive, Hard Disks, CD/DVD drive, Pen drive and magnetic tapes are some of the secondary storage devices.
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I.T. for Management Chapter 4 Secondary Storage Devices
Secondary Storage Devices• Most business information and particularly transactions require semi permanent storage• The primary storage is Volatile in nature• I.e all information is lost when power is switched off• Hence the need of secondary devices
Secondary Storage Devices• Some of commonly used secondary devices – Floppy Disks & drive – Hard disks – CD/DVD Drive – Pen drive – Magnetic tapes
Secondary Storage Devices Floppy DisksThe first floppy diskettes were introduced in the year 1971The floppy disk is packaged in a 8 inch square soft plastic envelope They had a capacity of 1 M.BLater in 1976 5.25 inch diskettes were introduced ………Cont.
Secondary Storage Devices Floppy DisksBasically, a floppy disk drive reads and writes data to a small, circular piece of metal-coated plastic similar to audio cassette tape. In this article, you will learn more about what is inside a floppy disk drive and how it works.You will also find out some cool facts about FDD’ s. …. cont
Secondary Storage Devices Floppy Disks Parts of a Floppy Disk Drive Floppy Disk Drive Terminology• Floppy disk - Also called diskette. The common size is 3.5 inches.• Floppy disk drive - The electromechanical device that reads and writes floppy disks.• Track - Concentric ring of data on a side of a disk.• Sector - A subset of a track, similar to wedge or a slice of pie. The Disk floppy disk is a lot like a cassette tape:•
Secondary Storage Devices Floppy Disks Parts of a Floppy Disk Drive• Both use a thin plastic base material coated with iron oxide. This oxide is a ferromagnetic material, meaning that if you expose it to a magnetic field it is permanently magnetized by the field.• Both can record information instantly.• Both can be erased and reused many times.• Both are very inexpensive and easy to use.
Secondary Storage Devices Floppy Disks Parts of a Floppy Disk DriveIf you have ever used an audio cassette, you know that it has one big disadvantage -- it is a sequential device.The tape has a beginning and an end, and to move the tape to another song later in the sequence of songs on the tape you have to use the fast forward and rewind buttons to find the start of the song, since the tape heads are stationary.For a long audio cassette tape it can take a minute or two to rewind the whole tape, making it hard to find a song in the middle of the tape.•
Secondary Storage Devices Floppy Disks• A floppy disk, like a cassette tape, is made from a thin piece of plastic coated with a magnetic material on both sides. However, it is shaped like a disk rather than a long thin ribbon. The tracks are arranged in concentric rings so that the software can jump from "file 1" to "file 19" without having to fast forward through files 2-18. The diskette spins like a record and the heads move to the correct track, providing what is known as direct access storage. In the illustration , you can see how the disk is divided into tracks (brown) and sectors (yellow).
Secondary Storage Devices Floppy Drive• The Drive The major parts of a FDD include: Read/Write Heads: Located on both sides of a diskette, they move together on the same assembly. The heads are not directly opposite each other in an effort to prevent interaction between write operations on each of the two media surfaces. The same head is used for reading and writing, while a second, wider head is used for erasing a track just prior to it being written.
Secondary Storage Devices Floppy Drive• This allows the data to be written on a wider "clean slate," without interfering with the analog data on an adjacent track.• Drive Motor: A very small spindle motor engages the metal hub at the center of the diskette, spinning it at either 300 or 360 rotations per minute (RPM).• Stepper Motor: This motor makes a precise number of stepped revolutions to move the read/write head assembly to the proper track position. The read/write head assembly is fastened to the stepper motor shaft.
Secondary Storage Devices Floppy Drive• Mechanical Frame: A system of levers that opens thelittle protective window on the diskette to allow theread/write heads to touch the dual-sided diskette media.An external button allows the diskette to be ejected, atwhich point the spring-loaded protective window on thediskette closes.• Circuit Board: Contains all of the electronics to handlethe data read from or written to the diskette. It alsocontrols the stepper-motor control circuits used to movethe read/write heads to each track, as well as themovement of the read/write heads toward the diskettesurface.
Secondary Storage Devices Floppy Drive• The read/write heads do not touch the diskette media when the heads are traveling between tracks. Electronic optics check for the presence of an opening in the lower corner of a 3.5-inch diskette (or a notch in the side of a 5.25-inch diskette) to see if the user wants to prevent data from being written on it.
Secondary Storage Devices Floppy DriveMerits:•In a floppy disk the files can be arranged Sequentially• or in a random mannerThe floppies being Removable makes it very easy totransportRequests for information can be answered quickly and atrandomDe Merits :The Floppy disks tend to get corrupted very easily becauseof which of these factorsFloppy have lesser storage spaceThey are sources of virus
Secondary Storage Devices Hard Disk Drive• IBM developed the idea of the Winchester or the hard disk The hard disks are enclosed in a hermetically enclosed container Capacities of the order of 20 GB,40 GB,80 GB are typical
Secondary Storage Devices Hard Disk Drive • How hard disk works:A hard disk works on the same principle of Floppy drive The entire assembly is permanently installed in the pcThe hard disk has one or more platter(disks) each with both sides which are recordableAll platters rotate on a central spindle at continuous speed are of the order of 7500 rpmSeveral read write heads are position on top of each rotating surfaceWhen the hard disk drive receives the instruction to read or write ,it uses the available data to locate the correct surface track & sector & reads or writes on it
Secondary Storage Devices Hard Disk Drive • How hard disk works:Hard disk is fast since it has to at most wait for the correct track or sector to come below read or write track,unlike floppy drive where the drive works in addition to searching for trackResponse time is of the order of 20 to 25 Millisecond is common
Secondary Storage Devices Hard Disk Drive• Here is a typical hard-disk drive: Front side
Secondary Storage Devices Hard Disk Drive• Here is a typical hard-disk drive: Backside
Secondary Storage Devices Hard Disk DriveIn order to increase the amount of information the drive can store, mosthard disks have multiple platters. This drive has three platters and sixread/write heads:Many drives use a "voice coil"approach -- the same technique usedto move the cone of a speaker on yourstereo is used to move the arm.
Secondary Storage Devices Hard Disk Drive• Merits: – Hard drive provides on line information & very fast. – Data access randomly & not sequentially – Extra hard disk can be added increasing storage capacity – Hard disks are hermetically sealed reducing chances of damage
Secondary Storage Devices Pen Drive What is pen driveA pen drive is a small removable Flash memory drive usually connected to the USB portIt provides storage ranging from 16 MB to several Giga bytesData can be stored as long as it is neededIt is plug & play deviceOS Xp automatically senses pen drive when inserted to USB portTypical dimensions are 77*25*9 mm
Secondary Storage Devices Pen Drive(Inside) Internals of a typical flash drive (Saitek brand USB1.1 pictured) 1 USB connector 2 USB mass storage controller device 3 Test points 4 Flash memory chip 5 Crystal oscillator 6 LED 7 Write-protect switch 8 Space for second flash memory chip
Secondary Storage Devices Pen Drive• Merits: – Massive storage capacity – Portable & compact – Solid state(no moving parts) hence less chance of corruption – USB compliant making easy to connect externally – Does not require external power source – Low cost (Rs 800-1000)
Secondary Storage Devices DVD• DVDs are of the same diameter and thickness as CDs, and they are made using some of the same materials and manufacturing methods. Like a CD, the data on a DVD is encoded in the form of small pits and bumps in the track of the disc.• A DVD is composed of several layers of plastic, totaling about 1.2 millimeters thick. Each layer is created by injection molding polycarbonate plastic. This process forms a disc that has microscopic bumps arranged as a single, continuous and extremely long spiral track of data.
Secondary Storage Devices DVD• Once the clear pieces of polycarbonate are formed, a thin reflective layer is sputtered onto the disc, covering the bumps. Aluminum is used behind the inner layers, but a semi-reflective gold layer is used for the outer layers, allowing the laser to focus through the outer and onto the inner layers.• After all of the layers are made, each one is coated with lacquer, squeezed together and cured under infrared light. For single-sided discs, the label is silk-screened onto the non readable side. Double-sided discs are printed only on the non readable area near the hole in the middle. Cross sections of the various types of completed DVDs (not to scale) look like this:
Secondary Storage Devices How DVD works• Each writable layer of a DVD has a spiral track of data. On single-layer DVDs, the track always circles from the inside of the disc to the outside. That the spiral track starts at the center means that a single- layer DVD can be smaller than 12 centimeters if desired.• What the image to the right cannot impress upon you is how incredibly tiny the data track is -- just 740 nanometers separate one track from the next (a nanometer is a billionth of a meter). And the elongated bumps that make up the track are each 320 nanometers wide, a minimum of 400 nanometers long and 120 nanometers high. The following figure illustrates looking through the polycarbonate layer at the bumps.
Secondary Storage Devices Data storage DVD/CD • DVDs can store more data than CDs for a few reasons: • Higher-density data storage • Less overhead, more area • Multi-layer storage• Higher Density Data Storage Single-sided, single-layer DVDs can store about seven times more data than CDs. A large part of this increase comes from the pits and tracks being smaller on DVDs.• Specification CD DVD• Track Pitch 1600 nanometers 740 nanometers• Minimum Pit Length (single-layer DVD) 830 nanometers 400 nanometers </FONT< td>• Minimum Pit Length (double-layer DVD) 830 nanometers 440 nanometers
Secondary Storage Devices DVD • Merits• Superior quality• Interactivity• Flexibility• Durability• Low cost• Compatibility• Can handle all kinds of data including sound & multimedia files• Many drives allow read/write of both CDS & DVD