physical storage media

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IntroductionAs you can imagine, the cost of managing huge amount of paper documents and their storagearea can be overwhelming, both in a monetary sense and in personal management sense. Indeed,this cost is often the main reason for business to switch to a computer base system. Computerbase system is:

1) Economical. It takes up far less space than paper documents.2) Secure. With use of storage control, data is usually safe from unauthorized users, and with useof back up systems that duplicate data is also safe from natural and People made disasters.3) Almost unlimited. There is virtually no limit to the amount of data that can be stored of-line.

Why Is Storage An Important Concept?Not understanding the concept of computer storage is not to understanding the concept of carsgasoline tank. Without using gasoline tank, you would not be able to get your car to go very farbecause, without the tank, you cannot use the gasoline. Similarly, if you do not use the storagedevice with your computer, you would not have the capability to store the data that will make

your computer useful.

In General, data is stored in the computer system for three principal reasons. First, current inputdata needs to be held for processing. For instance, the sales order data is input and storedtemporarily in a transaction file until the need arises to produce invoice. Second, some type ofdata is stored in relatively permanent basis and retrieves as required during processing. Forexample to produce customer invoice, you need data from customer file: customers name,address, billing instructions, and terms. Third, data is stored to be periodically updated. In ourcase, after the invoice have been produced, the account receivable file (reflecting what customerowes) need to be updated to reflect the last purchase. In additional to all this data, computersoftware instruction must be stored in a computer- usable from because a copy of the software

must be read into the main memory from a storage device before data processing can begin.Traditionally the most important part of every computer is the central processing unit (CPU, orsimply a processor), because it actually operates on data, performs any calculations, and controlsall the other components.Processor without a memory would not be a computer, merely a simple digital signal processingdevice, able to perform a fixed operation and immediately output the result. It would have to bere-built to change its behaviour, like in case of a calculator. The ability to store and change bothinstructions and data, the important von Neumann's idea, makes computers versatile. It basicallyintroduces the concept of computer programming, as opposed to re-building the hardware.A computer can exist that uses the single type of storage for all the data. However, to provideacceptable computer performance at a lower cost, computers usually use a whole storage

hierarchy. The traditional division of storage to primary, secondary, tertiary and off-line storageis based on the speed and cost per bit. The lower a storage is in hierarchy, the bigger is itsdistance from the CPU.

Data Representation: Binary CodeWhen you begin to write a report, you have quite collection of symbols to choose from: theletters A-Z, both upper and the lower case; the numerous punctuation and other symbols $ and%. People understand what these character means; computer cannot. Computers deal with the

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data converted in to simplest form that can be processed magnetically or electronically, that is,binary form. The binary is used to refer to two distinct states, on or off, yes or no, present orabsent, 1 or 0.For example, a light switch can be either on or off, so it can be viewed as a binarydevice. When data is stored on magnetic tape or disk, it appears as the presence or absence, Onor Off, of magnetic spots.

To store and process data in binary form, a way of representing characters, numbers, and othersymbols had to be developed. In other words, coding schemes had to be devised as standardizedmethods of encoding data for use in computer storage and processing.

Scheme for encoding data using a series of binary digits is called a binary code. A binary digit(bit) is either the character 1 (on) or the character 0(off). It represents one of two distinct state-magnetically, electrically, or optically.

The acronym ASCII stands for the American Standard Code for Information Interchange, whichis widely to represent characters in microcomputers and many minicomputers becausemicrocomputers operate on data in 8-bit groups ASCII uses 8 bit to represent a character, only 7bits are meaningful, but u do not need to worry about that. For example character A in ASCII in01000001.

The acronym EBCDIC refers to Extended Binary Code Decimal Interchange Code. Which is themost popular code used for IBM compatible mainframe computers. Unlike ASCII, this schemeuses all 8 bits to represent data in EBCDIC A is 11000001.

Primary and Secondary Storage

The term primary storage referees to the main memory of the computers, where both data andinstructions are held for immediate access and use by the computer central processing. Althoughtechnology is changing, most primary storage today is considered a Volatile form of storage,meaning that the data and the instruction are lost when the computer is turned off. Secondarystorage (or auxiliary storage) is any storage device designed to retain data and instructions in amore permanent form. Secondary storage is nonvolatile, meaning that the data and instructionsremain intact when the computer is turned off.

Primary Storage Unit

Random Access Memory (RAM).

Ram stands for Random Access Memory. As the name suggests data or instruction could beaccessed quickly/randomly from the RAM. It is a temporary/volatile memory i.e. what ever dataor instruction is in RAM would be lost when the computer is switched off. Also whenthe program is been completely executed it is automatically removed from the RAM .Theinformation stored in RAM could be read, written, modified or erased. RAM stores the usersdata, instruction, intermediate and final result temporally.

Read-only memory (ROM)

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Read-only memory (usually known by its acronym, ROM) is a class of storage media used incomputers and other electronic devices. Because data stored in ROM cannot be modified (at leastnot very quickly or easily), it is mainly used to distribute firmware (software that is very closelytied to specific hardware, and unlikely to require frequent updates).Modern semiconductor ROM chips are not immediately distinguishable from similar chips like

RAM modules, except by the part numbers printed on the package.

Secondary Storage Devices

Most Business information and particularly Transactions require semi-permanent Storage i.e. weneed to store a transaction for either further processing or references. It should also be possible toedit and update such transactions. Primary Storage such as the RAM though fastcannot be used for this purpose due to the sheer size of the information that an organizationneeds to store over a period of time. Further primary storage is volatile in nature. I.e. allinformation in the primary storage is lost as soon the power is turned off or the programmewhich has generated or is processing the information completes it job.

Some of the commonly used secondary storage devices include:

Floppy Disks and Drives

Hard Disks

CDs/DVDs and CD/DVD drives

Pen Drives.

Primary Storage UnitRAM:The key benefit of RAM over types of storage which require physical movement is that retrievaltimes are short and consistent. Short because no physical movement is necessary, and consistentbecause the time taken to retrieve a piece of data does not depend on its current distance from aphysical head; it requires practically the same amount of time to access any piece of data storedin a RAM chip. Most other technologies have inherent delays for reading a particular bit or byte.The disadvantage of RAM over physically moving media is cost, and the loss of data whenpower is turned off.

Because of this speed and consistency, RAM is used as 'main memory' or primary storage: theworking area used for loading, displaying and manipulating applications and data. In most

personal computers, the RAM is not an integral part of the motherboard or CPUit comes in theeasily upgraded form of modules called memory sticks or RAM sticks about the size of a fewsticks of chewing gum. These can quickly be removed and replaced should they becomedamaged or too small for current purposes. A smaller amount of random-access memory is alsointegrated with the CPU, but this is usually referred to as "cache" memory, rather than RAM.

Modern RAM generally stores a bit of data as either a charge in a capacitor, as in dynamic RAM,or the state of a flip-flop, as in static RAM. Some types of RAM can detect or correct random

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faults called memory errors in the stored data, using RAM parity and error correction codes.

Secondary Storage DevicesFloppy Disk

What is Floppy Disk and Disk Drive?< The first diskettes were introduced in 1971.

< They had a capacity of one megabyte i.e. roughly 1Million Bytes or characters

< The diskettes are placed in a drive, which has read and write heads.

< Later in 1976, 5.25 diskettes were introduced.

< They were inexpensive and easy to work with.

< Like the 8 diskettes, he 5.25 was soft and flexible. Therefore they were named floppy disks.

< In 1987 IBMs revolutionary PS/2 PCs were introduced and with them the 3.5 hard diskettewe know today.

How does it Work?

< The floppy disk is packaged in a 3.5-inch square hard plastic envelope.

< It has a long slit for read-write head access.

< And a hole in the centre for mounting the disk drive hub.

< The disk is logically divided into Tracks and Sectors; data is written/read from these sectors bya read write head. Except in the earlier days, reading and writing is done on tracks on both sidesof the diskette.

< Floppy disks are made of magnetic oxide-coated Mylar computer tape material.

< These diskettes have a thinner magnetic coating, allowing more tracks on a smaller surface.

< The track density is measured in TPI (trackes per inch).

< The TPI has been increased from 48 to 96 and now 135 in the 3.5 diskettes.

< When the computer requests the drive to be accessed, the floppy revolves on the centralspindle while the read write head picks up data.

Merits

< Floppies make it possible to store an infinite amount of information since the data can spanmultiple floppies.

< Requests for information can be answered quickly and at random.

< Files can be arranged sequentially or in a random manner.

< Floppies being removable make it a very easy way it transport data from one computer andlocation to another.

Demerits

< Floppy disks tend to get corrupted very fast either due to physical handling or due to dirt,moisture, radiation etc

< Compatibility of the drive and alignment of the head has often been a cause of problems whenusing a floppy from one machine onto another.

< Floppy disks have lesser storage space and transfer rates as compared to several other new

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Pen DriveWhat is a Pen Drive?

A pen drive is a small removable FLASH MEMORY DRIVE usually connected to the USBport of a computer.

It provides storage ranging from 16MB, to several Gigabytes. Data can be stored for as long as required even up to 10 years.

It is a Plug and Play device.

Typical Dimensions are approx. 77mm*25mm*9mm and weight of approx 20 grams.- It isthus compact and easy to carry around even in your pocket.

How does it Work

The pen drive is really a memory chip. It therefore does not have any moving electromechanical parts. The computer reads/writes to the Pen Drive as it would to the RAM. This ispossible since the Flash Memory card (pen Drive) is directly connected to the USB bus just asthe memory is connected to the bus.

The drive can be connected and in an instance a Windows based computer recognizes thepresence of the drive, loads the necessary driver (special software required to read or write.

The Pen Drive also has a write protect tab just like a floppy drive has.

This prevents the computer from writing to the driver if the user so wishes.

Merits

Massive Storage Capacity

Portable and Compact

Solid-State (No moving internal parts) hence less chance of damage and corruption.

Provides useful features such as Write-Protect switch (stops you accidentally erasing any

data), LED Read/Write Indicator (You can see when the drive is working), Password protectionsoftware included to protect your data.

It is USB Compliant making it easy to connect externally to any computer making it plug andpay. It therefore does not suffer from in-compatibility issues such as those faced in Floppy disksetc.

Does not require an external source of power.

It provides very fast rates up to 12mbit per second at full speed.

Very Affordable starts at approx Rs 800/--Rs 1000/- at the low end.

CDs.

What are CDs?

A Compact Disc or CD is an optical disc used to store digital data, originally developed forstoring digital audio. The CD, available on the market since late 1982, remains the standardplayback medium for commercial audio recordings to the present day, although it has lost groundin recent years to MP3 players, which have greater storage capability (albeit with lower soundquality).

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An audio CD consists of one or more stereo tracks stored using 16-bit PCM coding at a samplingrate of 44.1 kHz. Standard CDs have a diameter of 120 mm and can hold approximately 80minutes of audio. There are also 80 mm discs, sometimes used for CD singles, which holdapproximately 20 minutes of audio. The technology was later adapted for use as a data storagedevice, known as a CD-ROM, and to include record-once and re-writable media (CD-R and CD-

RW respectively). CD-ROMs and CD-Rs remain widely used technologies in the computerindustry as of 2007. The CD and its extensions have been extremely successful: in 2004, theworldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007, 200billion CDs had been sold worldwide.

DVDsWhat are DVDs?DVD (also known as "Digital Versatile Disc" and "Digital Video Disc") is a popular optical discstorage media format used for data storage. Its main uses are for movies, software, and dataarchiving. Most DVDs are of the same dimensions as compact discs (CDs) but store more than 6times the data.

The term DVD is used in describing three ways that data is stored on the disks DVD-ROMhas data which can only be read and not written, DVD-R can be written once and then functionsas a DVD-ROM, and DVD-RAM holds data that can be re-written multiple times.

Physical Formats

DVD-R - is a DVD recordable format. A DVD-R has a larger storage capacity than its opticalpredecessor, the 700 MB CD-R, typically storing 4.71 GB (or 4.382 GiB), although the capacityof the original standard developed by Pioneer was 3.95 GB (3.68 GiB). Pioneer has alsodeveloped an 8.54 GB dual layer version, which appeared on the market in 2005. Data on aDVD-R cannot be changed, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple(1000+) times

DVD-RAM - (DVDRandom Access Memory) is a disc specification presented in 1996 bythe DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers.

DVD-RAM media have been used in computers as well as camcorders and personal videorecorders since 1998. The direct successor of this format will be HD DVD-RAM

DVD+RW - is the name of a standard for optical discs: one of several types of DVD, whichhold up to about 4.7GB per disc (interpreted as approximately 4.7 109 bytes; actually 2295104sectors of 2048 bytes each) and are used for storing films, music or other data.DVD+RW supports random write access, which means that data can be added and removedwithout erasing the whole disc and starting over (up to about 1000 times). With suitablesupport from the operating system, DVD+RW media can thus be treated like a large floppy disk,in contrast to DVD-RW which must be erased before re-writing can take place.

DVD+RW was primarily developed for holding discrete data sets (which change with time) or asrecyclable discs for backing up collections of files. However, they (and DVD-RW) are lesspopular for computer use than DVD-R or DVD+R discs, because they are not suitable forpermanent backup files (because non-rewritable media is significantly cheaper). For similarreasons, rewritable discs are not as widely used for permanent storage of home DVD video

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recorders as DVD-R and DVD+R

Logical Formats

DVD-VIDEO - is a standard for storing video content on DVD media. In the U.S., weeklyDVD-Video rentals first out-numbered weekly VHS cassette rentals in June 2003, illustrating the

rapid adoption rate of the technology in the marketplace.Though many resolutions and formats are supported, most consumer DVD-Video disks useeither 4:3 or 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720480 (NTSC) or720576 (PAL). Audio is commonly stored using the Dolby Digital (AC-3), Digital TheaterSystem (DTS) formats, ranging from monaural to 5.1 channel "Surround Sound" presentations,and/or MPEG-1 Layer 2. Although the specifications for video and audio requirements vary byglobal region and television system, many DVD players support all possible formats. DVD-Video also supports features like menus, selectable subtitles, multiple camera angles, andmultiple audio tracks

DVD-AUDIO - is a format for delivering high-fidelity audio content on a DVD. It offersmany channel configuration options (from mono to 5.1 surround sound) at various sampling

frequencies. Compared with the CD format, the much higher capacity DVD format enables theinclusion of either considerably more music (with respect to total running time and quantity ofsongs) or far higher audio quality (reflected by higher linear sampling rates and higher verticalbit-rates, and/or additional channels for spatial sound reproductionDespite DVD-Audio's superior technical specifications, there is debate as to whether theresulting audio enhancements are distinguishable to typical human ears. DVD-Audio currentlyforms a niche market, probably due to its dependency upon new and relatively expensiveequipmentHow does a CD/DVD work?

A DVD is composed of several layers of plastic & each layer is created by injection moldingpolycarbonate plastic.

In a DVD, Data is encoded in the form of small pits and bumps in the track of the disc. Theencoding is done by a sharp laser beam. While reading the laser beam detects the pits and bumpsand the combination of these gives a stream of bits which can interpreted as characters by thecomputer.

Meritso Superior qualityo Interactivityo Flexibilityo Durabilityo Low Cost

o Compatibilityo Can handle all kinds of data including sound and multimedia files.o Unlimited storage since it is a removable medium-thus data can span across multipleCDs/DVDs. In addition each DVD/CD can take upwards of 600 GB of data which is quite large.Many Drives today allow read/write of both CDs and DVDs making them even more flexible touse.

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Tertiary storage ortertiary memory,[3] provides a third level of storage. Typically it involves arobotic mechanism which will mount (insert) and dismount removable mass storage media into a

storage device according to the system's demands; this data is often copied to secondary storagebefore use. It is primarily used for archival of rarely accessed information since it is much slowerthan secondary storage (e.g. 560 seconds vs. 1-10 milliseconds). This is primarily useful forextraordinarily large data stores, accessed without human operators. Typical examples includetape librariesand optical jukeboxes.

When a computer needs to read information from the tertiary storage, it will first consult acatalog database to determine which tape or disc contains the information. Next, the computerwill instruct a robotic arm to fetch the medium and place it in a drive. When the computer hasfinished reading the information, the robotic arm will return the medium to its place in thelibrary.

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http://en.wikipedia.org/wiki/Tertiary_storage#cite_note-2http://en.wikipedia.org/wiki/Tertiary_storage#cite_note-2http://en.wikipedia.org/wiki/Tape_libraryhttp://en.wikipedia.org/wiki/Tape_libraryhttp://en.wikipedia.org/wiki/Optical_jukeboxhttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Industrial_robothttp://en.wikipedia.org/wiki/Tertiary_storage#cite_note-2http://en.wikipedia.org/wiki/Tape_libraryhttp://en.wikipedia.org/wiki/Optical_jukeboxhttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Industrial_robot

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