Overview Of Various Data Storage Computer Science Essay

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In this survey paper we are providing the overview of various data storage techniques(magnetic, semiconductor and optical).This paper covers the storage techniques range from oldest magnetic tape to latest hologram data storage and 3D optical memory. the capacity and some of the basic information is presented in this paper.So, starting from the the old memories,we will be having the overview of various memory techniques which are available in the market or will be coming soon.


Storing of data is very important and basic requirement of today's life. All the applications we are using requires the storage of many programms and day by day the applications are improoving andthe memory requirement is increasing. and to meet the current storage requirement we are reached to holography and 3D optical storing techniques,as for various multimedia applications the storage need is increasing day by day. memories are categerised in 3types

a) magnetic storage

b) semiconductor storage

c) optical storage



Magnetic disk storage is used in mechanical hard drives to keep track of permanent information. Main memory, on the other hand, is used by RAM chips to store the data temporarily that the computer needs to calculate and track the programs it runs.



The biggest advantage of magnetic disk storage over main memory is persistence of data. The RAM chips that house our main memory contain large numbers of tiny electric switches, each stores a bit of information. When the power goes off, all of that information disappears forever. hard drive, on the other hand, has a magnetic platter covered with tiny zones of charged magnetic fields. Those magnetic fields stay there, storing our information even when we aren't actively using our computer.


One of the greatest things about magnetic disk storage is its ability to fit a tremendous amount of information into a small amount of space. Hard drives stay the same size but are able to fit more and more information onto magnetic platters. High-end hard-drive storage is measured in terabytes -- thousands of gigabytes of information.


Since the beginning of computing, hard drives have come down in price, and they continue to do so. Main memory also has become a lot cheaper, but its storage limitation is still a big factor. A RAM stick often holds less than 1 percent of the data capacity of a hard drive with the same price.

various types of magnetic memories are:-

1.delay line memory:-

Delay line memory is not used now a days but it was used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay line memory was a refreshable memory, but it was not like modern random-access memory as it was sequential-access. In its earliest forms, information introduced to the memory in the form of electric pulses which was transduced into mechanical waves that propagated relatively slowly through a medium, such as a cylinder filled with a liquid like mercury, a magnetostrictive coil, or a piezoelectric crystal. The propagation medium should be enoughcapable so that it could support the propagation of hundreds or thousands of pulses at single time instant. Upon reaching the other end of the propagation medium(at destination), the waves were re-transduced into electric pulses, amplified, shaped, and reintroduced to the propagation medium at the beginning, and then it refresh the memory.

2.core dump memory:-

In computing, a core dump, memory dump, or storage dump consists of the recorded state of the working memory of a computer program at a specific time, generally when the program has terminated abnormally (crashed), due to power failure or any other hardware failure etc. Core dumps are often used to assist in diagnosing and debugging errors in computer programs.

The term "core dump", "memory dump", or just "dump" has become jargon to indicate any storing of a large amount of raw data for further examination or for the future use.

Core dumps can serve as useful debugging aids in several situations. On early standalone or batch-processing systems, core dumps allowed a user to debug a program without monopolizing the (very expensive) computing facility for debugging; a printout could also be more convenient than debugging using switches and lights. On shared computers, whether time-sharing, batch processing, or server systems, core dumps allow off-line debugging of the operating system, so that the system can go back into operation immediately(access time of the system reduces or it increases the speed of the system). Core dumps allow a user to save a crash for later or off-site analysis, or comparison with other crashes.

3.Twistor memory:-

Twistor is a form of computer memory, similar to core memory, formed by wrapping or closing magnetic tape around a current-carrying wire.Twistor was similar in concept, but to store the patterns it replaced the circular magnets with magnetic tape. The tape was wrapped, in such a way that it formed a 45-degree helix, around one set of the wires, say X. The Y wires were replaced by solenoids wrapping a number of twistor wires. Selection of a particular bit was the same as in core, with one X and Y line being powered, generating a field at 45 degrees. The magnetic tape was selected specifically only to allow magnetization along the length of the tape, so only a single point of the twistor would have the right direction of field to become magnetized.

4. Bubble memory:-

Bubble memory is a type of non-volatile computer memory. It uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains. Each stores one bit of data. Bubble memory started out as a very promising technology in the 1970s, but failed commercially because of hard disk performance and cost improvements in the 1980s overtook its advantages.

5.Thin film memory:-

Thin-film memory is a high-speed variation of core memory developed by Sperry Rand in a government-funded research project. Instead of threading individual ferrite cores on wires, thin-film memory consisted of 4 micrometre thick dots of permalloy, an iron-nickel alloy, deposited on small glass plates by vacuum evaporation techniques and a mask. To provide very fast access times (in the range of 670 nanoseconds)the drive and sense lines were then added using printed circuit wiring over the alloy dots , but it was very expensive to produce.


Semiconductor memory is an electronic data storage device, implemented on a semiconductor-based integrated circuit.It is often used as computer memory. It is made in many different types and technologies. This memory has the property of random access, which means that it takes the same amount of time to access any memory location, so data can be efficiently accessed in any random order, it increases the speed of the system, which is opposite of data storage media such as hard disks and CDs which read and write data consecutively and therefore data can be accessed in only that way in which it was written.Hence due to random access semiconductor memories has faster access times than other types of data storage(a bit can access in nanoseconds). For these reasons it is used for computer memory. Shift registers, processor registers, data buffers and other small digital registersalso store digital data but they have no memory address decoding mechanism, so they are not considered as memory .A volatile memory is something which loses its stored data when the power to the memory chip is turned off, although it can be faster and less expensive than non-volatile memory. Main memory in most computers is of this type, as data is stored on the disk while the computer is off.




GRAETER CAPACITY that can be produced from small I'Cs ( intergrated circuits).

Major types are:


1. DRAM (Dynamic random-access memory)

It uses memory cells to store a bit consisting of one capacitor and one transistor. The reason why it is used for the main memory in computers is this as it is cheapest and highest in density. , But the memory cells must be periodically refreshed (rewritten) because the electric charge that stores the data in the memory cells slowly leaks off requiring additional circuitry. The refresh process in this is automatic and transparent to the user.

2. SDRAM (Synchronous dynamic random-access memory)

This was a reorganization of the DRAM memory chip, It was made to operate in synchronism with the computer's memory bus clock by adding a clock line. The chip has an internal command pipeline so it works on several memory accesses simultaneously.

3. DDR SDRAM (Double data rate SDRAM)

This was an increased data rate modification, which make the chip capable of transfering double memory data (two consecutive words) on one clock cycle by double pumping, transferring data on both the leading and trailing edges of the clock pulse. Extensions of this idea are the current (2012) technique being used to increase memory access rate and bandwidth. Since it is very difficult or becoming impractical to further increase the internal clock speed of memory chips. So, to increase data rates these chips transfer the data in larger blocks:

DDR2 SDRAM transfers 4 consecutive words per internal clock cycle

DDR3 SDRAM transfers 8 consecutive words per internal clock cycle.

DDR4 SDRAM transfers 16 consecutive words per internal clock cycle. It is scheduled to debut in 2012.

RDRAM (Rambus DRAM) is an alternate double data rate memory standard which was used on some Intel systems but ultimately disappears because of DDR SDRAM.

4. SGRAM (Synchronous graphics RAM)

It is a specialized type of SDRAM made for graphics adaptors. It was able to perform graphics-related operations such as bit masking and block write, and other important feature was that it can open two pages of memory at once.

5. PSRAM (Pseudostatic RAM)

It is a DRAM and to perform memory refresh on the chip it has circuitry , hence it save energy for the external memory controller can be shut down . It is used only in some portable game controllers such as the Wii.

6. SRAM (Static random-access memory)

It relies on digital flip-flop formed by several transistors to store each bit.Although it is less dense and more expensive per bit than DRAM, but it is faster and moreover it does not require memory refresh. Its main use is for smaller cache memories in computers .

7. Content-addressable memory:-

It is a special type of memory in which a data word is applied and the memory returns the location if the word is stored in the memory, instead of accessing data using an address. It is mainly incorporated in other chips where it is used for cache memory,such as microprocessors.

Nonvolatile memory preserves the data stored in it during periods even when the power to the chip is turned off. Therefore it is used for the memory in such devices, which don't have disks, and if have then it for removable memory cards among other uses(portable devices). Major types are:


This type of memory is designed to hold the data permanently, and its main normal operation is only read, not written. Although in some types of memory we can write too, but the writing process is slow and in this case usually all the data in the chips must be rewritten at once. It is mostly used to store system software which must be immediately accessible to the computer, for example the BIOS program whose main task is to start the computer, and the software for portable devices and embedded computers such as microcontrollers.

1. Mask programmed ROM

In this type of ROM the data is programmed into the chip during manufacturing process, so it is used only for large production runs.

2. PROM (Programmable read-only memory)

In this type of ROM the data is written into the chip before its installation in the circuit, but we can write only once. The data is written by plugging the chip into PROM programmer (device name).

3. EPROM (Erasable programmable read-only memory)

In this type of ROM the data contained in it can be rewritten by following steps

1.removing the chip from the circuit board,

2.exposing it to an ultraviolet light to erase it, and

3. plugging it into a PROM programmer.

It is mostly used for prototypes and small production run devices, where the program it is having must be changed at the factory.

4. EEPROM (Electrically erasable programmable read-only memory)

In this type of ROM the data can be rewritten electrically, while the chip is on the circuit board, but in this the writing process is slow. This is mainly used to hold the BIOS program in most computers, so that it can be updated as per requirment.

5. Flash memory

In this type the speed of writing process is intermediate between EEPROMS and RAM memory; it can be written too, but not as fast as enough to serve as main memory. It is mostly used to store files, as a semiconductor version of a hard disk,. It is mainly used in portable devices such as PDAs, USB flash drives, and removable memory cards which are used in digital cameras and cellphones.

6. MRAM (Magnetoresistive random-access memory)

It is a non-volatile random-access memory technology which is under development since the 1990s.Because of continued increases in density of existing memory technologies â€" mainly flash RAM and DRAM â€" kept it in a niche role in the market, but its proponents believe that the advantages of MRAM are so overwhelming that it will eventually become dominant for all types of memory and soon will be considered as a universal memory.


Optical storage is a term from engineering which refers to the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, mostly a beam of laser light precisely focused on a spinning disc. There are also some other means of optically storing data and some of the new methods are under development. Optical storage is a different form of data storage that make use of other technologies such as magnetism or semiconductors.

Optical storage can range from a single drive reading a single CD-ROM to multiple drives reading multiple discs such as an optical jukebox. Single compact discs can hold around 700MB (megabytes) and optical jukeboxes can hold much more.

The term optical drive oftenly refers to a device in a computer that can read CD-ROMs or other optical discs.

It was estimated in 2007 that the optical storage will represent 27% of the world's technological capacity to store information.


Durability. optical media can last a long time, depending on what kind of optical media you choose, but proper care is required.

Great for archiving. Several forms of optical media are write-once read-many, which means that when data is written to them, they cannot be reused for writing but data can be read by user as many times. This is an advantage for archiving because if data is written then data is preserved permanently with no possibility of being overwritten.

Transportability. Optical media is used on many platforms, such as PC. For example, the data written on a DVD-RAM can easily read on a PC or any other system which will be having an optical device and the same file system.

Random access. Optical media provide the capability to pinpoint a particular piece of data stored on it and it is independent of the other data on the volume or the sequence in which that data was stored on the volume.


Not-Reusable :- May be the write-once read-many (WORM) characteristic of some optical media makes it good for archiving, but it also prevents us from being able to use that particular media again.

Writing time:- The server uses software compression to write compressed data to our optical media. This process takes considerable processing unit resources and this may increase the time required to write and restore that data.

1. optical jukebox

An optical jukebox is basically a robotic data storage device which can automatically load and unload optical discs, such as Compact Disc, DVD, Ultra Density Optical or Blu-ray disc and it can also provide terabytes (TB) and petabytes (PB) of tertiary storage. These devices are oftenly known as robotic drives , optical disk libraries or autochangers. The Jukebox devices may have a picking device that traverses the slots and drives and they have up to 2,000 slots for disks. The arrangement of the slots and picking devices affects its performance, depending on the space between a disk and the picking device.In the optical technology seek times and transfer rates can vary.

Jukeboxes are used in imaging, medical, and video that is high-capacity archive storage environments. migration is a process in which little-used or unused files from fast magnetic storage to optical jukebox devices, it is done by Hierarchical storage management. when there is a need of any file, they are migrated back to magnetic disk. Also for making backups and in disaster recovery situations optical disc libraries are useful. Today data archiveing is one of the most important uses of jukeboxes. Archiving data is different from backups because in that the data is stored on media and it will last up to 100 years. The data can't erased or changed as it is written on Write Once Read Many (WORM) type discs.

optical disc drive:-

Optical disc drives are an integral part of stand-alone consumer appliances which include CD players, DVD players and DVD recorders. They are used in computers to read software and consumer media distributed on disc, and to record discs for archival and data exchange purposes very commonly.As we know that Optical media are cheap and have vastly higher capacity to handle the large files used since the days of floppy discs, and we also know that the vast majority of computer systems and most of the consumer entertainment hardware have optical writers.

optical tape:-

Optical tape is an optical storage medium which generally consist of a long and narrow strip of plastic on to which patterns can be written and from which the patterns can be read back. It also shares some technologies with cinema film stock and optical discs, but it is not compatible with either of them. The primary motivation behind the development of this technology was the possibility of far greater storage capacities than magnetic tape or optical discs.

hologram memory:-

Holographic data storage is a volumetric concept, that is it stores data throughout the volume(not only on the surface like previous existing memories) and it contains information using an optical interference pattern within a thick, photosensitive optical material. Light coming from a single laser beam is divided into two separate optical patterns of dark and light pixels. By the adjustment of the the reference beam angle, wavelength, or media position, a multitude of holograms (theoretically it can be upto several thousand) can be stored on a single volume.


Holographic memory allows a user to write something to disc and has a capability of saving that data up to 50 years. As magnetic storage degrades over time, and mechanical issues generally lead to the failure of the disk itself.The contact which is required by the Magnetic storage between a reader and the recording surface generally results in breakdown in about five years. On the other hand, overcoming this drawback of magnetic memory, the holographic storage requires no points of direct contact, because it uses lasers.

Faster Data Retrieval

In Holographic data storage data is stored multi-dimensionally rather than linearly , so, it allows for faster data retrieval (as it allows multiple points to be accessed simultaneously). For this reason holographic data storage can provide transfer speeds of up to 1 GB per second. Holographic systems are able to do this because they retrieve whole pages of data, roughly 60,000 bits of data, within a single pulse of light ,which is really very high as compared to traditional storage mediums such as DVDs as they can only transfer one bit of data per pulse.

3D optical data storage

As the name suggest that it is a kind of memory or storage technique in which information can be recorded and/or read with three dimensional resolution.

This new innovation has enough potential that it can provide petabyte-level mass storage on just DVD-sized disks.The process of Data recording and readback are achieved by focusing lasers within the medium. However, it is also of volumetric nature and therefore because of the volumetric nature of the data structure, the laser light must travel through other data points before it reaches the point where reading or recording is desired. Therefore, here some kind of nonlinearity is required to ensure that other data points will not interfere with the addressing of the desired point.

No commercial product based on 3D optical data storage has yet arrived on the mass market, although many companies (IBM etc.)are actively developing the technology and they are claiming that it may become available "soon".


In this paper we have seen basic features of various memories, their advantages and applications and how further developments are occured as applications increases and hence storage requirments increases. Today we are moving forward to hologram technique and 3D optical storage to meet the storage requirement of this multimedia world. It will be a big and satisfactory acheviement for all capacity hunger multimedia applications and advancements.


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