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Shweta Vanjari
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primary & secondary storage devices - April 2nd, 2008

Index



 Introduction
 Primary and Secondary Storage
 Random Access Memory (RAM)
 Floppy Disk
 Hard Disk Drive
 Pen Drive
 CDs
 DVDs
 Summary
 Reference




Introduction
As you can imagine, the cost of managing huge amount of paper documents and their storage area 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. Computer base 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 use of 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 car’s gasoline tank. Without using gasoline tank, you would not be able to get your car to go very far because, without the tank, you cannot use the gasoline. Similarly, if you do not use the storage device 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 input data needs to be held for processing. For instance, the sales order data is input and stored temporarily in a transaction file until the need arises to produce invoice. Second, some type of data is stored in relatively permanent basis and retrieves as required during processing. For example to produce customer invoice, you need data from customer file: customer’s name, address, billing instructions, and terms. Third, data is stored to be periodically updated. In our case, after the invoice have been produced, the account receivable file (reflecting what customer owes) need to be updated to reflect the last purchase. In additional to all this data, computer software 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, or simply a processor), because it actually operates on data, performs any calculations, and controls all the other components.
Processor without a memory would not be a computer, merely a simple digital signal processing device, able to perform a fixed operation and immediately output the result. It would have to be re-built to change its behaviour, like in case of a calculator. The ability to store and change both instructions and data, the important von Neumann's idea, makes computers versatile. It basically introduces 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 provide acceptable 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 storage is based on the speed and cost per bit. The lower a storage is in hierarchy, the bigger is its distance from the CPU.

Data Representation: Binary Code
When you begin to write a report, you have quite collection of symbols to choose from: the letters 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 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 or absent, 1 or 0.For example, a light switch can be either on or off, so it can be viewed as a binary device. When data is stored on magnetic tape or disk, it appears as the presence or absence, “On” or “Off”, of magnetic spots.
To store and process data in binary form, a way of representing characters, numbers, and other symbols had to be developed. In other words, coding schemes had to be devised as standardized methods 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, which is widely to represent characters in microcomputers and many minicomputers because microcomputers operate on data in 8-bit groups ASCII uses 8 bit to represent a character, only 7 bits are meaningful, but u do not need to worry about that. For example character A in ASCII in 01000001.

The acronym EBCDIC refers to Extended Binary Code Decimal Interchange Code. Which is the most popular code used for IBM compatible mainframe computers. Unlike ASCII, this scheme uses 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 and instructions are held for immediate access and use by the computer central processing. Although technology 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. Secondary storage (or auxiliary storage) is any storage device designed to retain data and instructions in a more permanent form. Secondary storage is nonvolatile, meaning that the data and instructions remain 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 be accessed quickly/randomly from the RAM. It is a temporary/volatile memory i.e. what ever data or instruction is in RAM would be lost when the computer is switched off. Also when
the program is been completely executed it is automatically removed from the RAM .The information stored in RAM could be read, written, modified or erased. RAM stores the user’s data, instruction, intermediate and final result temporally.

Read-only memory (ROM)
Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified (at least not very quickly or easily), it is mainly used to distribute firmware (software that is very closely tied 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. we need to store a transaction for either further processing or references. It should also be possible to edit and update such transactions. Primary Storage such as the RAM though fast
cannot be used for this purpose due to the sheer size of the information that an organization needs to store over a period of time. Further primary storage is volatile in nature. I.e. all information in the primary storage is lost as soon the power is turned off or the programme which 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 Unit
RAM:
The key benefit of RAM over types of storage which require physical movement is that retrieval times are short and consistent. Short because no physical movement is necessary, and consistent because the time taken to retrieve a piece of data does not depend on its current distance from a physical head; it requires practically the same amount of time to access any piece of data stored in 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 when power is turned off.

Because of this speed and consistency, RAM is used as 'main memory' or primary storage: the working 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 CPU—it comes in the easily upgraded form of modules called memory sticks or RAM sticks about the size of a few sticks of chewing gum. These can quickly be removed and replaced should they become
damaged or too small for current purposes. A smaller amount of random-access memory is also integrated 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 faults called memory errors in the stored data, using RAM parity and error correction codes.














Secondary Storage Devices
Floppy 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 IBM’s revolutionary PS/2 PC’s were introduced and with them the 3.5” hard diskette we 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 by a read write head. Except in the earlier days, reading and writing is done on tracks on both sides of 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 central spindle while the read write head picks up data.





Merits
 Floppies make it possible to store an infinite amount of information since the data can span multiple 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 and location 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 when using a floppy from one machine onto another.
 Floppy disks have lesser storage space and transfer rates as compared to several other new devices such as CD-ROMS and pen drives. Hence is data volumes are high floppies can become a very clumsy and unreliable was of storage and transport.
 People have broken through security provisions and gained access to sensitives as these can also source of viruses etc.
















Hard Disk Drives

 IBM developed the idea of a Winchester or Hard Disk
 A Hard disk is a device and a storage medium which is permanently fixed into the computer.
 Hard disks of the available as well desired for storage have to be bought along with computer.
 Capacities of the order of 20GB, 30GB, 40GB, and 60 GB are typical on many desktops.

How does it Work?
 A hard disk works on the same principle as a floppy drive. However unlike a floppy drive the entire assembly is permanently installed in the PC. The Hard Disk usually has one or more platters (i.e. Disks) each with both the sides which are recordable.
 All the platters rotate on a central spindle at a continuous speed. Typical speeds are of the order of 7500 rpm.
 Several read write heads are position on top of each rotating surface.
 When the hard disks drive receives an instruction to read or write information, it uses the available data to locate the correct surface track and sector and reads or writes data on it.
 The hard disk is fast since it has to at most wait for the correct track and sector to come below the read write head. Unlike a floppy drive where the drive works in addition to searching for the track and sector works on a start-stop mode.
 Response time of the order of 20-25 milliseconds is quite common.









Merits
 Hard drives provide on-line information and are very fast.
 Data can be accessed randomly and not just sequentially as it happens in some devices such as tapes.
 Most computer configurations allow extra hard disks to be added thereby making it possible to increase the on-line storage incrementally.
 Hard Disks are enclosed in a hermetically closed container thereby reducing the chance of damage and are therefore a fairly reliable mans of on-line storage.

Demerits
 The amount of storage is restricted by capacity of the disk installed at that time on his computer. Hence data has to be constantly removed/bacledup. This could impose limitations for some applications. However of a much higher capacity than enquired to take care of this issue.
 Though usually Hard Disks are reliable they can crash due to a mechanical defect or electrical surges which may have a damaging effect. Hence a back up on floppies or tapes of atleast the critical data needs to be kept for such eventualities.

















Pen Drive
What is a Pen Drive?
 A pen drive is a small removable FLASH MEMORY DRIVE usually connected to the USB port 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 is thus 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 electro mechanical parts. The computer reads/writes to the Pen Drive as it would to the RAM. This is possible since the Flash Memory card (pen Drive) is directly connected to the USB – bus just as the memory is connected to the bus.
 The drive can be connected and in an instance a Windows based computer recognizes the presence 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 protection software included to protect your data.
 It is USB Compliant making it easy to connect externally to any computer making it plug and pay. It therefore does not suffer from in-compatibility issues such as those faced in Floppy disks etc.
 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 for storing digital audio. The CD, available on the market since late 1982, remains the standard playback medium for commercial audio recordings to the present day, although it has lost ground in recent years to MP3 players, which have greater storage capability (albeit with lower sound quality).

An audio CD consists of one or more stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard CDs have a diameter of 120 mm and can hold approximately 80 minutes of audio. There are also 80 mm discs, sometimes used for CD singles, which hold approximately 20 minutes of audio. The technology was later adapted for use as a data storage device, 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 computer industry as of 2007. The CD and its extensions have been extremely successful: in 2004, the worldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide.



























DVDs
What are DVDs?
DVD (also known as "Digital Versatile Disc" and "Digital Video Disc") is a popular optical disc storage media format used for data storage. Its main uses are for movies, software, and data archiving. Most DVDs are of the same dimensions as compact discs (CDs) but store more than 6 times the data.
The term DVD is used in describing three ways that data is stored on the disks — DVD-ROM has data which can only be read and not written, DVD-R can be written once and then functions as 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 optical predecessor, the 700 MB CD-R, typically storing 4.71 GB (or 4.382 GiB), although the capacity of the original standard developed by Pioneer was 3.95 GB (3.68 GiB). Pioneer has also developed an 8.54 GB dual layer version, which appeared on the market in 2005. Data on a DVD-R cannot be changed, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple (1000+) times
 DVD-RAM - (DVD–Random Access Memory) is a disc specification presented in 1996 by the 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 video recorders 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, which hold up to about 4.7GB per disc (interpreted as approximately 4.7 × 109 bytes; actually 2295104 sectors 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 removed without erasing the whole disc and starting over (up to about 1000 times). With suitable
support 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 as recyclable discs for backing up collections of files. However, they (and DVD-RW) are less popular for computer use than DVD-R or DVD+R discs, because they are not suitable for permanent backup files (because non-rewritable media is significantly cheaper). For similar reasons, rewritable discs are not as widely used for permanent storage of home DVD video 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., weekly DVD-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 use either 4:3 or 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL). Audio is commonly stored using the Dolby Digital (AC-3), Digital Theater System (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 by global region and television system, many DVD players support all possible formats. DVD-Video also supports features like menus, selectable subtitles, multiple camera angles, and multiple audio tracks
 DVD-AUDIO - is a format for delivering high-fidelity audio content on a DVD. It offers many 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 the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction
Despite DVD-Audio's superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable to typical human ears. DVD-Audio







currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment
How does a CD/DVD work?
 A DVD is composed of several layers of plastic & each layer is created by injection molding polycarbonate plastic.
 In a DVD, Data is encoded in the form of small pits and bumps in the track of the disc. The encoding is done by a sharp laser beam. While reading the laser beam detects the pits and bumps and the combination of these gives a stream of bits which can interpreted as characters by the computer.

Merits
o Superior quality
o Interactivity
o Flexibility
o Durability
o Low Cost
o Compatibility
o 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 multiple CDs/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 to use.











Summary

Various forms of storage, based on various natural phenomena, have been invented. So far, no practical universal storage medium exists, and all forms of storage have some drawbacks. Therefore a computer system usually contains several kinds of storage, each with an individual purpose.

Processor without a memory would not be a computer, merely a simple digital signal processing device, able to perform a fixed operation and immediately output the result. It would have to be re-built to change its behaviour, like in case of a calculator. The ability to store and change both instructions and data, the important von Neumann's idea, makes computers versatile. It basically introduces 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 provide acceptable 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 storage is based on the speed and cost per bit. The lower a storage is in hierarchy, the bigger is its distance from the CPU.

Primary storage, presently known as memory, is the only one directly accessible to the CPU. CPU continuously reads instructions stored there and executes them. Any data actively operated on is also stored there in uniform manner. RAM is zeroed after computer powers on. If a computer contained only RAM, the CPU would not have a place to read any instructions from. Hence a non-volatile primary storage is used, containing small initial program, both to perform hardware power-on self test, and to bootstrap, that is, to read the larger program from






non-volatile secondary storage to RAM and execute it. A non-volatile technology known as read-only memory (ROM) is used for this purpose.

Secondary storage most business information and particularly Transactions require semi-permanent Storage i.e. we need to store a transaction for either further processing or references. It should also be possible to edit and update such transactions. Primary Storage such as the RAM though fast cannot be used for this purpose due to the sheer size of the information that an organization needs to store over a period of time. Further primary storage is volatile in nature. I.e. all information in the primary storage is lost as soon the power is turned off or the programmed which 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.











Reference




 It For Management.
-By Pradeep Pendse.


 Information Technology For Management
-By C.S.V Murthy.


 Introductions to computers
-By NIIT Computers.
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Re: primary & secondary storage devices - February 25th, 2016

Quote:
Originally Posted by shwetas_52 View Post
Index



 Introduction
 Primary and Secondary Storage
 Random Access Memory (RAM)
 Floppy Disk
 Hard Disk Drive
 Pen Drive
 CDs
 DVDs
 Summary
 Reference




Introduction
As you can imagine, the cost of managing huge amount of paper documents and their storage area 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. Computer base 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 use of 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 car’s gasoline tank. Without using gasoline tank, you would not be able to get your car to go very far because, without the tank, you cannot use the gasoline. Similarly, if you do not use the storage device 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 input data needs to be held for processing. For instance, the sales order data is input and stored temporarily in a transaction file until the need arises to produce invoice. Second, some type of data is stored in relatively permanent basis and retrieves as required during processing. For example to produce customer invoice, you need data from customer file: customer’s name, address, billing instructions, and terms. Third, data is stored to be periodically updated. In our case, after the invoice have been produced, the account receivable file (reflecting what customer owes) need to be updated to reflect the last purchase. In additional to all this data, computer software 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, or simply a processor), because it actually operates on data, performs any calculations, and controls all the other components.
Processor without a memory would not be a computer, merely a simple digital signal processing device, able to perform a fixed operation and immediately output the result. It would have to be re-built to change its behaviour, like in case of a calculator. The ability to store and change both instructions and data, the important von Neumann's idea, makes computers versatile. It basically introduces 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 provide acceptable 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 storage is based on the speed and cost per bit. The lower a storage is in hierarchy, the bigger is its distance from the CPU.

Data Representation: Binary Code
When you begin to write a report, you have quite collection of symbols to choose from: the letters 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 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 or absent, 1 or 0.For example, a light switch can be either on or off, so it can be viewed as a binary device. When data is stored on magnetic tape or disk, it appears as the presence or absence, “On” or “Off”, of magnetic spots.
To store and process data in binary form, a way of representing characters, numbers, and other symbols had to be developed. In other words, coding schemes had to be devised as standardized methods 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, which is widely to represent characters in microcomputers and many minicomputers because microcomputers operate on data in 8-bit groups ASCII uses 8 bit to represent a character, only 7 bits are meaningful, but u do not need to worry about that. For example character A in ASCII in 01000001.

The acronym EBCDIC refers to Extended Binary Code Decimal Interchange Code. Which is the most popular code used for IBM compatible mainframe computers. Unlike ASCII, this scheme uses 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 and instructions are held for immediate access and use by the computer central processing. Although technology 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. Secondary storage (or auxiliary storage) is any storage device designed to retain data and instructions in a more permanent form. Secondary storage is nonvolatile, meaning that the data and instructions remain 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 be accessed quickly/randomly from the RAM. It is a temporary/volatile memory i.e. what ever data or instruction is in RAM would be lost when the computer is switched off. Also when
the program is been completely executed it is automatically removed from the RAM .The information stored in RAM could be read, written, modified or erased. RAM stores the user’s data, instruction, intermediate and final result temporally.

Read-only memory (ROM)
Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified (at least not very quickly or easily), it is mainly used to distribute firmware (software that is very closely tied 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. we need to store a transaction for either further processing or references. It should also be possible to edit and update such transactions. Primary Storage such as the RAM though fast
cannot be used for this purpose due to the sheer size of the information that an organization needs to store over a period of time. Further primary storage is volatile in nature. I.e. all information in the primary storage is lost as soon the power is turned off or the programme which 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 Unit
RAM:
The key benefit of RAM over types of storage which require physical movement is that retrieval times are short and consistent. Short because no physical movement is necessary, and consistent because the time taken to retrieve a piece of data does not depend on its current distance from a physical head; it requires practically the same amount of time to access any piece of data stored in 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 when power is turned off.

Because of this speed and consistency, RAM is used as 'main memory' or primary storage: the working 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 CPU—it comes in the easily upgraded form of modules called memory sticks or RAM sticks about the size of a few sticks of chewing gum. These can quickly be removed and replaced should they become
damaged or too small for current purposes. A smaller amount of random-access memory is also integrated 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 faults called memory errors in the stored data, using RAM parity and error correction codes.














Secondary Storage Devices
Floppy 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 IBM’s revolutionary PS/2 PC’s were introduced and with them the 3.5” hard diskette we 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 by a read write head. Except in the earlier days, reading and writing is done on tracks on both sides of 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 central spindle while the read write head picks up data.





Merits
 Floppies make it possible to store an infinite amount of information since the data can span multiple 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 and location 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 when using a floppy from one machine onto another.
 Floppy disks have lesser storage space and transfer rates as compared to several other new devices such as CD-ROMS and pen drives. Hence is data volumes are high floppies can become a very clumsy and unreliable was of storage and transport.
 People have broken through security provisions and gained access to sensitives as these can also source of viruses etc.
















Hard Disk Drives

 IBM developed the idea of a Winchester or Hard Disk
 A Hard disk is a device and a storage medium which is permanently fixed into the computer.
 Hard disks of the available as well desired for storage have to be bought along with computer.
 Capacities of the order of 20GB, 30GB, 40GB, and 60 GB are typical on many desktops.

How does it Work?
 A hard disk works on the same principle as a floppy drive. However unlike a floppy drive the entire assembly is permanently installed in the PC. The Hard Disk usually has one or more platters (i.e. Disks) each with both the sides which are recordable.
 All the platters rotate on a central spindle at a continuous speed. Typical speeds are of the order of 7500 rpm.
 Several read write heads are position on top of each rotating surface.
 When the hard disks drive receives an instruction to read or write information, it uses the available data to locate the correct surface track and sector and reads or writes data on it.
 The hard disk is fast since it has to at most wait for the correct track and sector to come below the read write head. Unlike a floppy drive where the drive works in addition to searching for the track and sector works on a start-stop mode.
 Response time of the order of 20-25 milliseconds is quite common.









Merits
 Hard drives provide on-line information and are very fast.
 Data can be accessed randomly and not just sequentially as it happens in some devices such as tapes.
 Most computer configurations allow extra hard disks to be added thereby making it possible to increase the on-line storage incrementally.
 Hard Disks are enclosed in a hermetically closed container thereby reducing the chance of damage and are therefore a fairly reliable mans of on-line storage.

Demerits
 The amount of storage is restricted by capacity of the disk installed at that time on his computer. Hence data has to be constantly removed/bacledup. This could impose limitations for some applications. However of a much higher capacity than enquired to take care of this issue.
 Though usually Hard Disks are reliable they can crash due to a mechanical defect or electrical surges which may have a damaging effect. Hence a back up on floppies or tapes of atleast the critical data needs to be kept for such eventualities.

















Pen Drive
What is a Pen Drive?
 A pen drive is a small removable FLASH MEMORY DRIVE usually connected to the USB port 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 is thus 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 electro mechanical parts. The computer reads/writes to the Pen Drive as it would to the RAM. This is possible since the Flash Memory card (pen Drive) is directly connected to the USB – bus just as the memory is connected to the bus.
 The drive can be connected and in an instance a Windows based computer recognizes the presence 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 protection software included to protect your data.
 It is USB Compliant making it easy to connect externally to any computer making it plug and pay. It therefore does not suffer from in-compatibility issues such as those faced in Floppy disks etc.
 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 for storing digital audio. The CD, available on the market since late 1982, remains the standard playback medium for commercial audio recordings to the present day, although it has lost ground in recent years to MP3 players, which have greater storage capability (albeit with lower sound quality).

An audio CD consists of one or more stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard CDs have a diameter of 120 mm and can hold approximately 80 minutes of audio. There are also 80 mm discs, sometimes used for CD singles, which hold approximately 20 minutes of audio. The technology was later adapted for use as a data storage device, 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 computer industry as of 2007. The CD and its extensions have been extremely successful: in 2004, the worldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide.



























DVDs
What are DVDs?
DVD (also known as "Digital Versatile Disc" and "Digital Video Disc") is a popular optical disc storage media format used for data storage. Its main uses are for movies, software, and data archiving. Most DVDs are of the same dimensions as compact discs (CDs) but store more than 6 times the data.
The term DVD is used in describing three ways that data is stored on the disks — DVD-ROM has data which can only be read and not written, DVD-R can be written once and then functions as 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 optical predecessor, the 700 MB CD-R, typically storing 4.71 GB (or 4.382 GiB), although the capacity of the original standard developed by Pioneer was 3.95 GB (3.68 GiB). Pioneer has also developed an 8.54 GB dual layer version, which appeared on the market in 2005. Data on a DVD-R cannot be changed, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple (1000+) times
 DVD-RAM - (DVD–Random Access Memory) is a disc specification presented in 1996 by the 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 video recorders 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, which hold up to about 4.7GB per disc (interpreted as approximately 4.7 × 109 bytes; actually 2295104 sectors 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 removed without erasing the whole disc and starting over (up to about 1000 times). With suitable
support 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 as recyclable discs for backing up collections of files. However, they (and DVD-RW) are less popular for computer use than DVD-R or DVD+R discs, because they are not suitable for permanent backup files (because non-rewritable media is significantly cheaper). For similar reasons, rewritable discs are not as widely used for permanent storage of home DVD video 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., weekly DVD-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 use either 4:3 or 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL). Audio is commonly stored using the Dolby Digital (AC-3), Digital Theater System (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 by global region and television system, many DVD players support all possible formats. DVD-Video also supports features like menus, selectable subtitles, multiple camera angles, and multiple audio tracks
 DVD-AUDIO - is a format for delivering high-fidelity audio content on a DVD. It offers many 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 the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction
Despite DVD-Audio's superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable to typical human ears. DVD-Audio







currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment
How does a CD/DVD work?
 A DVD is composed of several layers of plastic & each layer is created by injection molding polycarbonate plastic.
 In a DVD, Data is encoded in the form of small pits and bumps in the track of the disc. The encoding is done by a sharp laser beam. While reading the laser beam detects the pits and bumps and the combination of these gives a stream of bits which can interpreted as characters by the computer.

Merits
o Superior quality
o Interactivity
o Flexibility
o Durability
o Low Cost
o Compatibility
o 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 multiple CDs/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 to use.











Summary

Various forms of storage, based on various natural phenomena, have been invented. So far, no practical universal storage medium exists, and all forms of storage have some drawbacks. Therefore a computer system usually contains several kinds of storage, each with an individual purpose.

Processor without a memory would not be a computer, merely a simple digital signal processing device, able to perform a fixed operation and immediately output the result. It would have to be re-built to change its behaviour, like in case of a calculator. The ability to store and change both instructions and data, the important von Neumann's idea, makes computers versatile. It basically introduces 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 provide acceptable 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 storage is based on the speed and cost per bit. The lower a storage is in hierarchy, the bigger is its distance from the CPU.

Primary storage, presently known as memory, is the only one directly accessible to the CPU. CPU continuously reads instructions stored there and executes them. Any data actively operated on is also stored there in uniform manner. RAM is zeroed after computer powers on. If a computer contained only RAM, the CPU would not have a place to read any instructions from. Hence a non-volatile primary storage is used, containing small initial program, both to perform hardware power-on self test, and to bootstrap, that is, to read the larger program from






non-volatile secondary storage to RAM and execute it. A non-volatile technology known as read-only memory (ROM) is used for this purpose.

Secondary storage most business information and particularly Transactions require semi-permanent Storage i.e. we need to store a transaction for either further processing or references. It should also be possible to edit and update such transactions. Primary Storage such as the RAM though fast cannot be used for this purpose due to the sheer size of the information that an organization needs to store over a period of time. Further primary storage is volatile in nature. I.e. all information in the primary storage is lost as soon the power is turned off or the programmed which 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.











Reference




 It For Management.
-By Pradeep Pendse.


 Information Technology For Management
-By C.S.V Murthy.


 Introductions to computers
-By NIIT Computers.
Hey Dear,

Here i am sharing Introduction on Secondary Storage, please check attachment below.
Attached Files
File Type: pdf Introduction on Secondary Storage.pdf (3.41 MB, 0 views)


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