The memory of a central processing unit i.e. Internal Memory is too limited and too expensive to serve the entire data storage needs of the typical user. Thus, most computer systems use secondary storage media i.e. backing storage or external memory.
The following characteristics are common to all the backing storage devices:
- Nonvolatile storage: This means that the data encoded on these media is not affected by a loss of electric power.
- Mass storage: This means that the secondary storage media i.e. backing storage can store a very large amount of data.
- Cost-efficiency: Secondary storage media can store more data, per unit cost, than CPU memory.
- Lack of computing capability: Secondary storage devices can only store data. They cannot perform any operation on data.
Two main categories of storage technology used today are magnetic storage and optical storage.
Primary magnetic storage: Magnetic storage devices store the data on a magnetically coated surface. They can generally be used many times. They tend to have a large storage capacity when compared to optical media. The main disadvantage is that the data held on these can be damaged if the device is put too close to a strong magnetic.
- Magnetic tape
- Hard disks (both fixed and removable)
- High capacity floppy disks
- Disk cartridges
- Diskettes
Primary optical storage: Optical storage devices are read by a laser beam. Generally they have a more limited storage capacity when compared to magnetic devices. However, one advantage is that they are more hard wearing than magnetic devices.
Another kind of storage device has recently emerged- Solid State Storage. Data storage made from silicon chips is called solid state storage. Solid state storage complements HDD storage and offers numerous benefits, including:
- Higher data transfer rate
- Faster I/O response times
- Lower power and cooling requirements
- Improved Input/Output Operations Per Second
- Reduced cost per IOPS and cost per Watt
Important :- Flash memory (a solid state-chip) is a type of electronically erasable programmable read-only memory (EEPROM), memory chips that retain information without requiring power. (This is different from flash RAM, which does need power to retain data.) Regular EEPROM erases content byte by byte; most flash memory erases data in whole blocks, making it suitable for use with applications where large amounts of data require frequent updates. Inside the flash chip, data is stored in cells protected by floating gates. Tunneling electrons change the gate's electronic charge in "a flash" (hence the name), clearing the cell of its contents so it can be rewritten.
Flash Applications
USB drives:
Introduced in 2002, USB drives encapsulate flash with a memory controller in a small package offering high capacity,
fast transfer rates, flexibility and convenience; some feature built-in hardware encryption and password protection.
Compared with floppy or optical drives,
USB flash drives store more data and provide easy file transfer between most devices with a USB interface.
Memory cards: These have evolved from the matchbook-size CompactFlash cards introduced in 1994
through 2001's postage-stamp-size Secure Digital cards to the latest miniSD and microSD cards,
with higher capacities and faster transfer speeds at every step.
Solid-state drives: The newest flash memory application, SSDs can replace a
computer's hard drive. They have no moving parts, so mechanical failure is near
zero. Solid-state drives are quieter and smaller than hard drives, and they
provide faster response, access and boot-up times but consume much less power and run cooler.
Traditional hard drives currently offer greater capacity and a lower price, but this will likely change.
Early concerns that flash memory's finite number of erase/write cycles
would be a problem are abating as warranties for
flash-based SSDs approach those of hard drives.
Backup:
is the activity of copying files or databases, so that their additional copies may
be restored in case of a data loss accident. Thus, we can emphasize first two aspects related to backup - storage media for data and depositories for backup media. Another important aspect is growing necessity in backup caused by development of computer technologies
and data volumes expansion. Data backup is essential to the survival of a business. There are only two options regarding the final destination of your backups: online or offline.
Online data backup is just as the name implies. Data is backed up over a networked connection to a remote location. An offline data backup most often refers to data that is backed up on-site, rather than to a remote location.
Personal backups of the data on your hard-drive can be made by
Businesses backup essential data by
Magnetic Tape: A Magnetic Tape is an secondary storage device that is made from a polyester base material coated with an oxide compound. It is the compound which gives the tape its durability and electromagnetic properties. Magnetic tape units are referred to as a sequential access medium because they store data in a chronological sequence.
Use
They are used in any application which requires extremely large storage capacity and
where the speed of access is not an issue, such as
- Used for backups of file servers for computer networks.
- Used in a variety of batch processing applications such as reading of bank cheques, payroll processing and general stock control.
- Cheap Storage
- Large Storage Capacity
- Ability to store unlimited length record
- Cost-effective as a backup medium for file secuity
- Fairly durable
- Non-human readable
- Specific records only found by sequentially searching through tape records
- Access is slow, so uses are limited
- Not flexible when file updating requires record insertion or deletion.Top↑
Hard Disks: Hard disk is still the most common storage device for all computers.
Hard drives store data in tracks divided into sectors. The hard disk and drive are a single unit which includes the hard
disk, the motor that spins the platters and a set of read/write heads. Because you
cannot remove the disk from the drive the terms hard disk and hard drive are used
interchangeably.
Hard drives have become the primary storage devices for PCs because they are
convenient and cost effective.
Use
Hard disks are essential in any system that requires fast data access time and fast data transfer rates.
- They are used in real time systems such as robotics, rocket launching etc.
- They are essential in any online system.
- The data transfer rate is fast.
- Data access times are fast.
- Large storage capacity.
- Direct Access storgae device.
- Non-human readable.
- They are easily damaged.
- A head crash – in which the head touches the disk – can destroy the data stored in the area of the crash. A severe head crash can destroy the read/write head.Top↑
Portable Hard Disks:
As their name suggests, they can be easily or conveniently transported from one system to another.
Use
They are used as backup media and for transferring large files from one computer to another.
Advantages
Disadvantages
CD-ROM: The familiar audio compact disk is a popular medium for storing music. In the
computer world, the medium is called compact disk read only memory (CD-ROM).
This uses the same technology used to produce music CDs.
The CD-ROM drive for music or data reads 0s and 1s from a spinning disk by
focusing a laser on the disks surface. Some areas of the disk reflect the laser light into
a sensor, other areas scatter the light. A spot that reflects the laser beam is interpreted
as a 1 and the absence of a reflection is interpreted as a 0.
Data is laid out on a CD-ROM disk in a long, continuous spiral that starts at the outer
edge and winds inwards towards the centre. Data is stored in the form of lands,
which are flat areas on the metals surface, and pits, which are depressions or hollows.
A land reflects the laser light into the sensor (a data bit of 1) and a pit scatters the light
(a data bit of 0).
On a full CD-ROM the spiral of data stretches almost 3 miles long.
A standard CD
can store 700 MB of data or about 80 mins of audio.
Use
They are used for applications which require the prevention of deletion of data, accidential or otherwise.
Advantages
Disadvantages
DVD-ROM:
Digital video (or versatile) disk read only memory, is a high-density medium capable
of storing a full-length movie on a single disk the size of a CD.
Achieves such high storage capacities by using both sides of the disk and special data
compression technologies. The latest generation of DVD-ROM use layers of data
tracks; the laser beam reads data from the first layer and then looks through it to read
data from the second layer.
Each side of a standard DVD-ROM can hold up to 4.7 GBThey are used for applications which require the prevention of deletion of data, accidential or otherwise. Dual layer DVD-ROM
can hold 17 GB of data.
Use
They are used for applications which require the prevention of deletion of data, accidential or otherwise.
- They are used in real time systems such as robotics, rocket launching etc.
- They are essential in any online system.
- More robust than hard disk.
- Portable.
- Slower data transfer rate.
- Difficulty in updating.Top↑
CD-R, DVD-R:
CD-R allows you to create your own CD-ROM disks that can be read by any CDROM
drive. After the information has been written to the CD it cannot be changed.
DVD-R allows you to create your own DVD-ROM disks that can be read by any DVDROM
drive. After the information has been written to the DVD it cannot be changed.
Use
They are used as backup media for MUSIC,MOVIE and DATA.
Advantages
Disadvantages
CD-RW, DVD-RW:
These are optical disks that allows writing, erasing, and rewriting.
Use
We can use these devices according to our requirement for storing data, television show, movie or music..
Advantages
Disadvantages
DVD-RAM:
The digital versatile disk random access memory, DVD-RAM is a newer technology. DVD-RAM is a type of optical disk with multigigabyte capacity that can be read, written, and erased. A DVD RAM uses a type of technology known as phase change on the physical disc to store the data. The disc has a special layer of material made from a mixture of metals which is highly responsive to heat. When the laser makes contact with it, one temperature will cause the alloy to be crystalline, while a higher temperature will turn it amorphous. Thus, it is possible to record binary data onto the disc for playback, and to erase the data and write over it later.
Use
If a computer user wants a highly flexible backup system which is capable of being rewritten numerous times, a DVD RAM is an excellent choice..
Advantages
Disadvantages
Blu-ray Disk:
Blu-Ray discs are one of the newcomers on the optical disc scene.
Although the technology is identical to CDs and DVDs, the fundamental difference with Blu-Ray is the laser that is used to read the discs. A blue laser (hence the name Blu-Ray) is used instead of the red lasers that are used on earlier discs. Blue lasers have a shorter wavelength (450 nanometers) than red lasers (650 nanometers), and therefore the beam can be focused on a smaller area which means that you can cram more data on an identically sized disc.
The Variations in the formats are as follows:
Use
Their main use is in home video game consoles.
Advantages
Disadvantages
PhotoCD: One popular form of recordable CD is PhotoCD, a standard developed by Kodak for storing digitised photographic images on a CD. Many film-developing stores now have PhotoCD drives that can store your photos and put them onto a CD.Top↑
