Magnetic storage devices

Magnetic storage devices

1. Name Bilal Maqbool
Department CS&IT
Class SE-I
Roll # 10
Assignment Magnetic Storage Devices
Submitted
to
Sir. Shujahat Hussain
Date 08/02/12
Day Wednesday
University University of Azad Jammu &
Kashmir
References
1. www.wikipedia.org
2. www.ehow.com
3. www.howstuffworks.com
4. Digital Electronics by Floyd
5. www.digitalelectronics.com

2. Data Storage Device
A data storage device is a device for recording (storing) information (data).
Recording can be done using virtually any form of energy, spanning from manual
muscle power in handwriting, to acoustic vibrations in phonographic recording, to
electromagnetic energy modulating magnetic tape and optical discs.
A storage device may hold information, process information, or both. A device that
only holds information is a recording medium. Devices that process information (data
storage equipment) may either access a separate portable (removable) recording
medium or a permanent component to store and retrieve information.
Different types of storage devices?
Different types of storage devices are best for different situations.
 RAM Electronic data storage device
 Hard disk Optical data storage device
 Floppy disk Magnetic data storage device
 CD ROM
 Tape
Electronic Data Storage Device
Electronic data storage is storage which requires electrical power to store and retrieve that data.
Most storage devices that do not require vision and a brain to read data fall into this category.
Electromagnetic data may be stored in either an analog or digital format on a variety of media. This
type of data is considered to be electronically encoded data, whether or not it is electronically stored
in a semiconductor device, for it is certain that a semiconductor device was used to record it on its
medium. Most electronically processed data storage media (including some forms of computer data
storage) are considered permanent (non-volatile) storage, that is, the data will remain stored when
power is removed from the device. In contrast, most electronically stored information within most
types of semiconductor (computer chips) microcircuits are volatile memory, for it vanishes if power
is removed.
With the exception of barcodes and OCR data, electronic data storage is easier to revise and may be
more cost effective than alternative methods due to smaller physical space requirements and the ease
of replacing (rewriting) data on the same medium. However, the durability of methods such as
printed data is still superior to that of most electronic storage media. The durability limitations may
be overcome with the ease of duplicating (backing-up) electronic data.
Optical Storage Devices
• An optical disk is a high-capacity storage medium.
An optical drive uses reflected light to read data.
• To store data, the disk's metal surface is covered with
tiny dents (pits) and flat spots (lands), which cause
light to be reflected differently.
• When an optical drive shines light into a pit, the light
cannot be reflected back. This represents a bit value
of 0 (off). A land reflects light back to its source,
representing a bit value of 1 (on).

3. Magnetic Storage Devices
Magnetic storage media and devices store data in the form of tiny magnetized dots. These
dots are created, read and erased using magnetic fields created by very tiny electromagnets.
In the case of magnetic tape the dots are arranged along the length of a long plastic strip
which has been coated with a magnetisable layer (audio and video tapes use a similar
technology).
In the case of magnetic discs (e.g. floppy disc or hard-drive), the dots are arranged in circles
on the surface of a plastic, metal or glass disc that has a magnetizable coating.
Magnetic storage and magnetic recording are terms from engineering referring to the
storage of data on a magnetized medium. Magnetic storage uses different patterns of
magnetization in a magnetizable material to store data and is a form of non-volatile memory.
The information is accessed using one or more read/write heads. As of 2011, magnetic
storage media, primarily hard disks, are widely used to store computer data as well as audio
and video signals. In the field of computing, the term magnetic storage is preferred and in
the field of audio and video production, the term magnetic recording is more commonly
used. The distinction is less technical and more a matter of preference.




History
Magnetic storage in the form of audio recording on a wire was publicized by Oberlin Smith
in 1888. He filed a patent in September, 1878 but did not pursue the idea as his business was
machine tools. The first publicly demonstrated (Paris Exposition of 1900) magnetic recorder
was invented by Valdemar Poulsen in 1898. Poulsen's device recorded a signal on a wire
wrapped around a drum. In 1928, Fritz Pfleumer developed the first magnetic tape recorder.
Early magnetic storage devices were designed to record analog audio signals. Computer and
now most audio and video magnetic storage devices record digital data.
In old computers, magnetic storage was also used for primary storage in a form of magnetic
drum, or core memory, core rope memory, thin film memory, twistor memory or bubble
memory. Unlike modern computers, magnetic tape was also often used for secondary
storage.

4. Magnetic recording classes
Analog recording
Analog recording is based on the fact that remnant magnetization of a given material depends on the
magnitude of the applied field. The magnetic material is normally in the form of tape, with the tape
in its blank form being initially demagnetized. When recording, the tape runs at a constant speed.
The writing head magnetizes the tape with current proportional to the signal. A magnetization
distribution is achieved along the magnetic tape. Finally, the distribution of the magnetization can be
read out, reproducing the original signal. The magnetic tape is typically made by embedding
magnetic particles in a plastic binder on polyester film tape. The commonly used magnetic particles
are Iron oxide particles or Chromium oxide and metal particles with size of 0.5 micrometers. Analog
recording was very popular in audio and video recording. In the past 20 years, however, tape
recording has been gradually replaced by digital recording.
Digital recording
Instead of creating a magnetization distribution in analog recording, digital recording only needs two
stable magnetic states, which are the +Ms and -Ms on the hysteresis loop. Examples of digital
recording are floppy disks and HDDs.
Magneto-optical recording
Magneto-optical recording writes/reads optically. When writing, the magnetic medium is heated
locally by a laser, which induces a rapid decrease of coercive field. Then, a small magnetic field can
be used to switch the magnetization. The reading process is based on magneto-optical Kerr effect.
The magnetic medium are typically amorphous R-FeCo thin film (R being a rare earth element).
Magneto-optical recording is not very popular. One famous example is Minidisc developed by Sony.
Domain propagation memory
Domain propagation memory is also called bubble memory. The basic idea is to control domain wall
motion in a magnetic medium that is free of microstructure. Bubble refers to a stable cylindrical
domain. Data is then recorded by the presence/absence of a bubble domain. Domain propagation
memory has high insensitivity to shock and vibration, so its application is usually in space and
aeronautics.
Technical details
Access method
Magnetic storage media can be classified as either sequential access memory or random or serial access
memory although in some cases the distinction is not perfectly clear. The access time can be defined as the
average time needed to gain access to stored records. In the case of magnetic wire, the read/write head only
covers a very small part of the recording surface at any given time. Accessing different parts of the wire
involves winding the wire forward or backward until the point of interest is found. The time to access this
point depends on how far away it is from the starting point. The case of ferrite-core memory is the opposite.
Every core location is immediately accessible at any given time.
Hard disks and modern linear serpentine tape drives do not precisely fit into either category. Both have many
parallel tracks across the width of the media and the read/write heads take time to switch between tracks and
to scan within tracks. Different spots on the storage media take different amounts of time to access. For a hard
disk this time is typically less than 10 ms, but tapes might take as much as 100 s.
Current usage
As of 2011, common uses of magnetic storage media are for computer data mass storage on hard disks and
the recording of analog audio and video works on analog tape. Since much of audio and video production is
moving to digital systems, the usage of hard disks is expected to increase at the expense of analog tape.
Digital tape and tape libraries are popular for the high capacity data storage of archives and backups. Floppy
disks see some marginal usage, particularly in dealing with older computer systems and software. Magnetic
storage is also widely used in some specific applications, such as bank cheques (MICR) and credit/debit cards
(mag stripes).

6. - How Magnetic Storage Works

• A magnetic disk's medium contains iron particles,
which can be polarized—given a magnetic charge—in
one of two directions.
• Each particle's direction represents a 1 (on) or 0 (off),
representing each bit of data that the CPU can
recognize.
• A disk drive uses read/write heads containing
electromagnets to create magnetic charges on the
medium.

Magnetic Storage Devices - Formatting

• Before a magnetic disk can be used, it must be
formatted—a process that maps the disk's surface and
determines how data will be stored.
• During formatting, the drive creates circular tracks
around the disk's surface, then divides each track into
sectors.
• The OS organizes sectors into groups, called clusters,
then tracks each file's location according to the clusters
it occupies.

Magnetic Storage Devices - Disk Areas

When a disk is formatted, the OS creates four
areas on its surface:
• Boot sector – stores the master boot record, a small
program that runs when you first start (boot) the
computer
• File allocation table (FAT) – a log that records each
file's location and each sector's status
• Root folder – enables the user to store data on the disk
in a logical way
• Data area – the portion of the disk that actually holds data

7. Types of Magnetic Storage
Hard Drive Storage Device
Hard drives are the most popular storage subsystem in the computers. Hard drives are responsible for
storing persistent info on a computer and due to its persistency it has been considered as the most
important computer storage system sold in the market.
Hard-drives have a very large storage capacity (up to 1TB). They can be used to store vast amounts
of data. Hard-drives are random access devices and can be used to store all types of films, including
huge files such as movies. Data access speeds are very fast.
Data is stored inside a hard-drive on rotating metal or glass discs (called ‘platters’).

Fixed Hard Drive
A hard-drive built into the case of a computer is known as ‘fixed’. Almost every computer has a
fixed hard-drive.
Fixed hard-drives act as the main backing storage device for almost all computers since they
provide almost instant access to files (random access and high access speeds).

Portable Hard Drive
A portable hard-drive is one that is placed into a small case along with some electronics that allow
the hard-drive to be accessed using a USB or similar connection.
Portable hard-drives allow very large amounts of data to be transported from computer to
computer.

Many portable music players (such as the iPod classic) contain tiny hard-drives. These miniature
devices are just not much bigger than a stamp, but can still store over 100MB of data!

8. Magnetic Tape Storage Device
A magnetic tape storage device contains a plastic tape that is coated with magnetic material, which
records characters in form of combinations of points on tracks parallel to longitudinal axis of tape. These
tapes are sequential media. There is a problem with magnetic tapes because every time access to
certain information becomes necessary to read all data that precedes it resulting in loss of time.
Magnetic tape is a large capacity, serial access medium. Because it is a serial access medium,
accessing individual files on a tape is slow.
Tapes are used where large amounts of data need to be stored, but where quick access to individual
files is not required. A typical use is for data back-up (lots of data, but rarely only accessed in an
emergency)
Tapes are also used and in some batch-processing applications (e.g. to hold the list of data that will
be processed).


Magnetic Drum Storage Device
Magnetic drum storage device contains either a hollow cylinder or a solid cylinder, which rotate at a
consistent velocity. These cylinders are covered with magnetic material that is capable of retaining
information, which is recorded and read by a head whose arm moves in the direction of the axis of
rotation of the drum. In magnetic drum, access to information is direct and not in a sequential pattern like
magnetic tapes.

Magnetic drum storage device by IBM

9. Floppy disk or Diskette Storage Device
A diskette or a floppy disk is a flexible plastic disk covered by magnetic material, which allows reading
and recording of limited data stored on it. A floppy disk is thin and flexible enclosed in a rectangular or
square thin shell of plastic. These disks are currently out of fashion. They are usually sized around 3½ to
5¼ inches and are still used in personal computers.
So above were the four types of magnetic storage devices of a computer system. In my next article, I will
share some info on Six Types of Optical Storage Devices of a Computer, which will help you in
understanding them before buying them.



Zip Disc
A removable and portable storage medium, similar in appearance to a floppy disk, but with a much
higher capacity (100MB, 250MB or 750MB).
Zip discs are random access devices which were used for data back-up or moving large files
between computers.
Another obsolete storage device, zip discs were a popular replacement for floppy discs for a few
years, but they never caught on fully before being superseded by cheaper media like CD-ROMs and
CD-Rs


Jaz Disc
A removable and portable storage medium based on hard-drive technology, with a large capacity
(1GB or 2GB).
Jaz discs are random access devices which were used for data back-up or moving large files
between computers.
Discs were expensive to buy and not very reliable.
Like the Zip disc, this system never really caught on and was superseded by far cheaper and more
reliable and cheaper technology.

10. The Advantages of Magnetic Storage
Best way to store data
It is a very well and cool way to store data.
Security of data
There are no huge security problems. You can take your data secure from unauthorized
persons/users.
Backup
You can store data as a backup and for the use in future for along time.
Larger space
It provides space in larger amount to store all data in one memory………………….
……………………………………………………………etc.
And Much More………………………….

The Disadvantages of Magnetic Storage
Magnetic tape is not as flexible as digital options.
Magnetic storage refers to magnetic tapes, which utilize a very thin layer of metal powder that is bonded
to a strip of plastic, the same technology that is used to make cassette tapes. Magnetic tapes are larger,
however, and can hold images of documents. Since they are hard copy and not affected by digital
problems, many companies use magnetic tapes as backups for important documents. However, the
format is not flawless.
Access Issues
Magnetic storage tape can record a variety of documents but in only one order. There has to be a
beginning and an end; the tape cannot just pull out requested data. This means that a person looking for
data at the end of the tape with have to cycle through all the data before it first, making the search for
data stored on magnetic tape more laborious than searches through digital storage.
System Issues
Magnetic tapes can work only with specific programs that take data and apply them to the magnetic film.
These systems are expensive. And even when the tapes are created, a separate machine is needed to
read them, adding to the cost. There may also be compatibility issues between different systems.
Cost
Magnetic storage was once popular because it was much more cost effective than downloading and
storing data on a hard drive long term. However, prices have leveled out, and now digital data storage,
especially on servers, can beat out magnetic storage in terms of price. Other aspects, like data security,
remain the same.
Magnetic Reactions
The magnetic film used on the tapes is reactive to other magnetic forces. Strong magnetic fields can
disrupt or destroy the information on the tapes. The film can also melt in intense heat, making fires a
danger among all forms of storage.
Future
A new type of magnetic storage, called Magnetoresistive Random Access Memory or MRAM, is
being produced that stores data in magnetic bits based on the tunnel magnetoresistance (TMR)
effect. Its advantage is non-volatility, low power usage, and good shock robustness. The 1st
generation that was developed was produced by Everspin Technologies, and utilized field induced
writing. The 2nd generation is being developed through two approaches: Thermal Assisted
Switching (TAS) which is currently being developed by Crocus Technology, and Spin Torque
Transfer (STT) on which Crocus, Hynix, IBM, and several other companies are working. However,
with storage density and capacity orders of magnitude smaller than an HDD, MRAM is useful in
applications where moderate amounts of storage with a need for very frequent updates are required,
which flash memory cannot support due to its limited.