Storage Devices

Storage Devices

by Ashish Bhatnagar

​Backing the Data

• Duplicate copy of the data to be used if the original data is lost.

• Original data can be lost due to accidental deletion, device malfunction, hacking, data corruption​, natural disaster, virus infection.

• ​Backup is also useful if the original data needs to be used elsewhere and modified.

​Measuring memory size

• Storage space is measured in Bytes where each byte is capable of storing a single piece of information.

• A byte consists of 8 bits (1 and 0)

​Primary and Secondary Storage

​Primary Storage

• is the essential storage space of a computer.

• ​Stores the data temporarily

• ​Accessible to the computer system (inaccessible to user)

​Secondary Storage

• ​Used by the user for own data storage

• ​Stores data permanently

• ​Store the data in huge amount

• ​Directly accessible to the user

​Magnetic Storage Devices

• Data is stored on a magnetized medium.

• ​Commonly used for storing audio and video data.

• ​Most commonly used storage medium.

​Fixed Internal Hard Drive

• Used in every modern computer

• Fast speed of data access

• Store huge amounts of data​

• ​Provides Direct Access of files. Any file on the disk at any location can be read instantly.

• ​Storage medium called "Platter" is coated in a magnetic medium that stores the data.

​Fixed Internal Hard Drive

• Used to store Operating system and application software in a computer.

• ​Application that needs a fast and immediate access to data uses a hard drive.

• Used to store the files in a file servers in a computer network.

• Used in game consoles, media servers and other systems where high speed of data transfer is required.​

​Advantages and Disadvantages of HDD

• Fast ​read and write speed

• ​Huge storage capacity

• ​Cost of per megabyte storage is very less

• ​Easily damaged due to shock or if unplugged improperly from the computer.

• ​Difficult to attach or detach from the computer as it is commonly inside the computer casing

​Portable Hard Drives

• ​Same as HDD but are connected externally to a computer via USB port.

• Very fast speed of data transfer.

• Comes with a protective covering for protection against physical damage.

• Portable. Easy to carry around.

• Can be encrypted or password protected for protection against data theft.​

Advantages and Disadvantages of Portable HDD​

​Serial Access

• ​Serial access is a term describing a group of elements being accessed in a predetermined, ordered sequence.

​Serial Access

• Serial files are read by starting at the beginning and reading through every record until you find the one that you want.

• ​Also called as Sequential Access.

• ​Used to store a large amount of data and speed in not important.

• ​Used in batch processing systems like payroll applications.

• ​Each individual piece of data is marked with a Start and a Stop.

​Direct Access

• ​Also called as Random Access method.

• ​Data is accessed by directly going to the memory location where it is stored by using an address.

• ​Direct access is suitable for the applications where immediate access to data is required.

• ​Example HDD, CD, Flash disk, SSD

• ​Address of a particular data is stored in a table.

​Magnetic Tape

• Magnetic tape is a medium for magnetic recording, made of a thin, magnetizable coating on a long, narrow strip of plastic film.

• ​Data is read using Serial Access method.

• ​Used in batch processing and offline system where a large volume of data is processed altogether.

• ​Slow data transfer speed.

​Advantages and Disadvantages of Magnetic Tape

• ​Less expensive

• ​Robust storage. Durability is high.

• ​Huge data storage capacity

• ​Fast Data Transfer speed

• ​Slow Data Access time

• ​Affected by strong magnetic fields.

• ​Updating the data is not a straight forward task

​Optical Storage Media

• ​Data is stored by the help of a low intensity Laser light.

• ​Laser light is used to create Pits and Bumps to store data in Binary format.

• ​Storage medium is coated with a light sensitive material

• ​CD, DVD, Blu Ray disk are examples of optical storage

​CD-ROM

• ​These are Read Only optical discs.

• ​They can only be read and data cannot be written on these discs.

• ​Data is stored at the manufacturing stage.

• ​Data is stores as a sequence of Pits (Binary 1) and Lands (Binary 0)

• ​Pits are formed by etching the surface with a laser light during the manufacturing stage.

• ​Data is stored on a track that spirals out from the center

​CD-ROM

• ​CD ROMs are used to store music, software and games.

• ​These are used where there is a need to prevent the deletion or manipulation of the stored data.

• ​Less expensive than Hard Drives.

• ​Slow data transfer rate than a HDD

​CD-R

• ​CD-R is recordable only once.

• ​Once recorded it becomes a CD-ROM.

  ​After manufacturing the CD-R is blank and data can be written by the user only once using a CD Writer device.

• ​If the CD-R is not completely filled by the data during the writing process then the empty space becomes unusable because CD-R can be written only once.

• ​Used for home recording of video and audio data

• ​A special CD Writer device is required to store the data.

​CD-RW

• ​RW is rewritable and data can be written and erased from this type of disk.

• ​They don't become a CD-ROM after data recording.

• ​They contain a phase changing layer which can be used to record the data or erase the data repeatedly.

• ​

​DVD-RAM

• ​It has concentric tracks for recording data

• ​Simultaneous read and write operations are possible

• ​It uses phase change technology in which a laser light is used to heat the surface of a phase changing alloy altering its optical reflectivity index.

• ​Durable

• ​Can be rewritten a large number of times

• ​Expensive

​Blue Ray Discs

• ​Uses a blue laser instead of red laser light

• ​Higher density of storage

• ​Lesser read errors due to presence of only one layer of plastic

• ​Protects data from piracy

• Expensive than other types of discs​

• ​Movie distribution, games distribution

​Solid State Storage

• ​These devices have no moving parts.

• ​Data is stored on silicon chips in binary format.

• ​Reliable data storage

• ​Light weight

• ​Faster as compared to magnetic disks

• ​Low power consumption

• ​Shorter life span as compared to magnetic disks

​Memory Stick

• ​Use SSD technology to store large amounts of data

• ​Connected to the computer through a USB port

• ​Plug and Play storage device

• ​For backup or transporting files between devices

• ​Easy to lose

• ​Incorrect removal of stick can lead to data loss

​Memory Card

• ​Use EEPROM memory for data storage

• ​Used in mobile phones and camera for data storage

• ​Expensive per GB storage of data