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Monday, July 14, 2008



Introduction: -
Computer mainly consists of three parts, namely – input devices, output devices and the Central Processing Unit (CPU). The CPU, in turn, consists of 3 parts-Memory, Arithmetic Logic Unit (ALU) and Control Unit. The memory is the ability of the computer to store information i.e. data. The data is stored in computer in the form of storage devices.
Computer is regarded as the most popular invention of the 21st century. Thus, computer is used in each and every field. All manual work done in organizations is now being done with the help of computer. Organizations have a large amount of data consisting of customer information, research, financial transactions etc. Computer has to perform some instructions on it and has to generate new data. Thus, new data is added everyday. New data generated and the old data processed can be required for future reference. For this purpose it has to be stored in some form of medium. The storage devices attached to the computer satisfy this purpose.
In some fields like weather forecasting, satellite transmission, nuclear technology tremendous amount of data is generated. For storing this data within the available resources, some special techniques have to be adopted.
So mankind has been trying to improve the quality of storage devices and developing new softwares. Thus , the constantly improving storage devices and softwares are included in the term ‘STORAGE SOLUTIONS’.

Computer memory: -
Computer memory is of 2 types-internal and external.
1. Internal memory: -

This type of memory is not useful for storing our data, the reasons being listed below. It is the computer’s own memory useful for its successful booting. Internal memory is broadly classified into 2 types, RAM and ROM.

a. RAM

System (main) memory is called RAM (Random Access Memory) and is most responsible for handling, operating and application needs. It is a read/write memory i.e. we can view as well as modify the contents of RAM. The contents of RAM are erased after the computer is switched off. Thus RAM belongs to the so-called volatile memory. The RAM has storage capacity in mega –bytes (MB). But it can be utilized to a larger capacity by using a software called as virtual memory i.e. by keeping memory in instant, with pieces of program being swapped between disk and memory as needed. Depending on the constructional features , RAM is of 2 types Static RAM(SRAM) and Dynamic RAM(DRAM).

b. ROM

ROM means Read Only Memory. The contents of ROM are read-only, but are not erased even if the computer is switched off. Thus it belongs to the non-volatile memory. The ROM contains system files required for the setup of the computer. ROM is of 3 types PROM(Programmable ROM) , EPROM(Erasable Programmable ROM) , EEPROM(Electrically Erasable ROM).PROM cannot be erased after recorded once. EPROM allows manufacturer to remove one set of instructions in exchange for another set. EEPROM is upgraded by flashing the chip using electrical methods and hence also known as FLASH ROM.

2. External Memory: -
There are 2 types of external memory namely, magnetic and optical.
Magnetic memory: -

There are 3 devices working on the principle of magnetic memory:-
a. Hard disk :-

Introduced in 1957, the IBM-made random access method of accounting and control (RAMAC) was the first disk drive. It consisted of 50 magnetic disks of 24-inch in diameter and rotating at 1200 RPM (rotations per minute). About 40 years later, the IBM Travelstar 6GT drive has 3 thin-film 2.5 inch disks and 6 ceramic sliders with the heads working on magneto-resistive principles and flying over the disk surface at only about a few dozens nm. The track density is 16,000 TPI (track per inch) and the areal density is 4.1 GB/in2.
. The HDD is used by a computer to store operating system (OS) and the user's data. Fierce competition between the drive manufacturers has pushed the cost of one MB of data to a very small number of $1 to $2 per MB making a HDD of several GB in capacity relatively inexpensive and easily affordable by almost anyone. The HDD is one of the most important components of the modern PC: no application will run reasonably without the hard drive. Continuous improvement of the head design allowed extremely high densities of magnetic recording with magnetic bits getting smaller and smaller. But, the head is only one component of the magnetic recording system, with magnetic media being extremely important as well. The first magnetic media was called "particulate media" because it included particles of iron oxide (as the magnetic medium) and aluminum oxide (for abrasive resistance). Modern magnetic media is called "thin-film media" and consists of very thin layers with a total thickness about 500 angstroms or 50 nm .
Every hard drive has one or many platters (which store magnetic data), usually twice as many sliders with magnetic heads (to read and write data), an actuator arm (to hold the suspension with the slider at the end), and a voice-coil actuator (to move the actuator when the head is accessing data). The drive is connected to the computer via the interface connector. Currently, the maximum capacity hard drive available is of 80 GB and data storage capacity is increasing day-by-day.

b. Floppy disk: -

In its design, the floppy disk is similar to the hard drive: it operates on the principles of magnetic recording, it uses magnetic heads for data storage and retrieval from the rotating magnetic media. The main differences are in the quality of the media (with much lower magnetic performance for the floppy) and low rotational speed of the disk - about 300 rotations per minute. Another difference - continuous contact between two spring-loaded sliders and the media is not, most likely, going to exist forever. Today's hard drives already show some level of slider-disk interference at much higher velocities (beyond 7500 rpm).
The capacity and data transfer rates of floppy drives saturated at extremely low levels (1.44 MB and about 0.06 MB/sec). These parameters could be improved dramatically with today's technology but... do not expect changes. There are millions and millions of floppy drives out there and it is too late to change standards. Today, the only two functions left for the floppy disks are serving as boot disks in the case of system conflicts on your PC and serving as movable storage for those who still live in the sub-two-megabytes-of-storage world. The main advantage of floppy drives is still low cost and universal compatibility.

c. Magnetic tapes :-
The magnetic tapes look somewhat like a tape of an audio cassette. They support serial access of data storage. They are not useful for storing our day-to-day data but are used for storing archival data. They have a slow data transfer rate as they have serial data access. Nowadays new types of magnetic tape i.e. DAT (Digital Audio Tape) are available. They are faster than normal tapes but are quite expensive.

Optical memory: -

Today’s meaning of optical data storage refers to storage systems that use light for recording and retrieval of information. Optical drives of all kinds operate on the same principle of detecting variations in the optical properties of the media surface. Optical recording potentially have much greater readability than magnetic recording systems since there is a much larger distance between read/write head and moving media. Another advantage of the optical recording systems over the best performing magnetic recording systems – hard drives -is their removability. The main disadvantage of the optical storage when compared to magnetic is slower data random access.


The CD-ROM is a prerecorded disc. It has a capacity of storing 700 MB of data or 74 minutes of audio files. The CD has a formation of lands and pits. The land and the pit refer to the flat surface and depressed surface respectively. If the laser reflects(after falling on a land)it gets reflected back and interpreted is interpreted as 1. While if the laser does not reflect but scatters(after falling on a pit)it is interpreted as 0.

b. CD-RW

The CD-RW is a read/write disc. Contents of this CD may be changed. But the speed of this CD is less than that of CD-ROM. They are expensive than CD-ROM but are quite useful because of their capacity of modifying the contents. Many materials exist in one or more states may have different optical properties. This phenomenon is ysed in CD-RW disks.

c. CD-R
Initially, a CD-R is blank. The structure of the disk is somewhat different from that of a CD-ROM, but they both have a similar substrate layer, protective layer, and reflective metal layer. The difference is really in the organic dye layer. The CD-R drive is different from the regular CD-ROM drive since its laser can operate on different power levels. The highest level burns the pits on the disk surface; the lowest reads the pits and lands without damaging the disk surface. The recording spiral starts, like in CD-ROM, from the inner radius of the disk and continues towards the outer edge of the disk till all required data are recorded or the data limit is reached. To simplify the head positioning mechanism, a special pre-groove is usually created on a blank CD-R. The laser beam can follow this groove during both data reading and writing. Standard CD-R disks are relatively inexpensive (less than $1-$2) and accommodates about 650 MB of data (or 74 minutes of audio recording).
The design of CD-R itself makes them write-once media, since it is impossible to erase the pits from the disk surface using the same laser. This is why the CD-R is a relatively inexpensive option for permanent data archiving and backup.
d. DVD
DVD initially stood for Digital VideoDisc but now stands for Digital Versatile Disc. Like a CD, DVD is an optical storage system for read-only, recordable and rewritable applications. But, being similar to a CD in many ways, DVD is considered to be a CD future replacement.
The main features of the DVD formats can be summarized as follows:
· Backwards compatibility with current CD media (at least the newest models of DVD drives)
· Physical dimensions identical to compact disc with total thickness equal to 1.2 mm, but with capacity at least 7 times larger than that of CD.
· Capacities of 4.7 GB, 8.54 GB, 9.4 GB, and 17.08 GB, depending on the disk structure.
· Single-layer/dual-layer and single/double sided options.
· DVD replication process is similar to that used for compact disks.
· A disc-based format means fast random access like in hard drives and CDs and unlike tapes.
· Designed from the outset for video, audio and multimedia. Meets the requirement for 133 minutes of high quality video on one side of a disk.
· DVD-ROM for enhanced multimedia and games applications.
· DVD-Video for full length high quality movies on one disc.
· DVD-Audio for higher quality music, surround sound and optional video, graphics and other features.
· All formats use a common file system.
The backward compatibility of the DVD drives means that it will read both CD-ROM and CD-audio, which makes them a great replacement for CD-drives. Because of higher bit density and other advantageous features, even a 5x-speed DVD drive will read the CD at the rate equivalent to about 40x for the regular CD drive. For now, DVD drives are, in general, more expensive, and require special MPEG-2 hardware or software decoders to read the compressed data. To have the best video quality, the hardware approach is better unless the fastest processors are used.
This clearly makes DVD-ROM a computer storage of the near future, especially for databases, multimedia, games, interactive video, etc.
e. Photo CD
The photo CD is used to store photos. This CD was developed by KODAK. These CD’s are of the read –only type i.e. data when once recorded, then it is not possible to modify it’s contents. This CD can be read using normal CD-ROM drives.

Some advanced removable devices:-

1. Clik drive

The Iomega Clik! drive is an attempt by Iomega to enter a new market of portable electronic devices such as digital cameras, phones, hand-help PCs, global positioning systems, etc. With its 40 MB of storage, Clik! The 40MB Clik! disk can hold approximately 40 mega-pixel images or hundreds of lower resolution images.
For this, you will need to download the images from your camera's removable flash memory card to the Clik! disk via the Clik! drive. Then, keep using the same memory card for more pictures. You can later download the pictures from the Clik! drive to your PC for editing, printing, etc. Clik! drives cost about $200 and disks are about $10.

2. IBM Microdrive

"real" storage devices such as IBM Microdrive (about the size of a flash memory card and capable of storing 170 MB or 340 MB of data) became available recently. The Microdrive can hold 1,000 digital compressed photographs or six hours of near CD-quality audio or 300 hefty novels or the equivalent of more than 200 standard-size floppy disks. Its MSRP (manufacturer’s suggested retail price) is about $500, which is expected to go down with time. Its weight is 16 grams.

3. ORB
Like Jaz drive, ORB is designed for data backup and exchange. Castlewood claims that their drive is faster (see comparison below) and more reliable. It also comes in all thinkable configurations, such as internal (EIDE, SCSI) and external (Parallel, SCSI, USB, IEEE 1394 Firewire). It is also available for both PC and Macintosh computers. Similar to Jaz, ORB drive can be used to store, backup, and move large office application files, digital music, presentations, digital photos, digital video, and to provide back-up for your OS. These products are much closer to the category of 'backup' storage than the infamous 100-MB and 250 MB Zip drives and have relatively large storage capacity even by today's standards.

4. Pen-drive

The pen-drive consists of a small cubical box for storing data. They are available in storage capacity of 64 MB, 28 MB, 256 MB and 512 MB. Currently they are expensive and the storage capacity is also not very large.

5. Jaz

Jaz disks can be used to store, backup, and move large office application files, digital music, presentations, digital photos, digital video, and to provide back up for your OS. These products are much closer to the category of 'backup' storage than the infamous Zip drives and have relatively large storage capacity even by today's standards. On the other hand, with the modern hard drive capacities exceeding 20 GB, back up with Jaz 2 GB disks is too expensive. One will need to spent about $1500 (including the cost of the drive itself) to back up a 20 GB hard drive. It is much cheaper to, for example, buy 1 more hard drive and back up you data on it, or, just go with tape storage.

6. Magneto-optical (MO) storage

The MO systems include basic principles of both magnetic and optical storage systems: MO systems write magnetically (with thermal assist) and read optically.
Presently, there are two standard form-factors used for MO systems: 5.5-inch and 3.5-inch, which are protected by hard envelops. The larger form-factor MO disks are capable of holding about as much as the standard CD-ROM. Under pressure from the inexpensive and relatively fast CD-R and CD-RW, MO drives seems to be losing ground. On the other hand, some of the principles of the MO technology (thermally assisted magnetic recording) may find their way into the most advanced magnetic storage devices of the future.

7. Removable HDD

The removable hard drive is a simple and effective way to meet your need for removable storage and data back up. Assuming you have a free IDE connector (SCSI removable drives are also available) and a free 3.5" floppy drive bay, installing a removable drive may be the cheapest (per GB of data) option for the storage-hungry PC user. In fact, there is almost nothing wrong with these removable drives, except for the little fact that they are far less popular than Zip or Jaz drives. The only thing needed is the docking bay (about $35 to $100 depending on quality and interface type), a key (provided with the drive for security reasons), and computer restart - and you have one extra hard drive! And this is a real hard drive with its large capacity and fast data transfer rates. With the today's falling price for HDDs, you can easily have about 10 mobile GBs of storage and backup.

Data Compression softwares: -

Winzip: -
Winzip is a software which compresses data i.e. a large amount of data is fit into small memory space. Eventually it helps to increase utility of storage devices.

Conclusion: -
Thus we have observed the different types of storage devices and we find that each one has its own advantages and limitations. Computer users have to function each of them for storing maximum data and thus reduce the amount of economy spent on storage devices.

References: -

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