Secondary Storage Devices

 

SECONDARY STORAGE DEVICES

Secondary storage (or external memory) :

Secondary storage is also known as external memory or non-volatile. It is slower than main memory. These are used for storing data/information permanently.

Cpu directly does not access these memories instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory, and then cpu can access it.

Characteristic of secondary memory

·         These are magnetic and optical memories.

·         It is known as backup memory.

·         It is non-volatile memory.

·         Data is permanently stored even if power is switched off.

·         It is used for storage of the data in the computer.

·         Computer may run without secondary memory.

·         Slower than primary memories.

Types of secondary storages

q  Magnetic tape

q  Hard disk        

q   floppy disk

q   optical disk

q   cds (compact disks)

q   dvds (digital versatile disc or digital video disc)

1)    Magnetic tapes:

The magnetic tapes is the type of secondary storage device and this device is used for taking back up of data

Structure and data storage method

Tape contains some magnetic fields and the magnetic tapes are used accessing the data into the sequential form and the tape also contains a ribbon which is coated on the single side of the tape and also contains a head which reads the data which is recorded on to the tape. And when we are reading the information from the disk then we can also read backward information means we can also back the tape for reading the previous information. And for inserting the tape into the system we also requires some tape drives which contains tape and which is responsible for reading the contents from the tapes.

Characteristics 

They can store huge amount of data into the tape drive , but the main limitation of the tape drive is that we cant access the data from the disks directly means if we wants to 100th record from the tape then we must have to move all the previous i.e. 99th records first. And the tapes are also easily damaged due to the human errors.

2)    Magnetic disks : -

This is also called as the hard disk

Structure and data storage method

This is made from the thin metal platter which is coated on the both sides of the magnetic disks. And the there are many plates or platters into a single hard disk and all the plates are made from the magnetic materials and all the disks are rotate from the 700 to 3600 rpm means rotation per minute and the hard disk also contains a head which is used for both reading and writing the data from the hard disks.

 

The plate of disk is divided into the tracks and sectors and the collection of tracks makes a cylinder means all the tracks of the disk which a consecutive areas makes a cylinder.

The disk is first divided into the number of tracks and the tracks are further divided into the sectors and the number of tracks makes a cylinder. All the data is stored into the disk by using some sectors and each sectors belongs to a tracks. The data is accessed from the disk by using the heads, all the heads have some arm those are used for reading the data from the particular tracks and sector. When the disk rotates very high speed then the head also moves, for reading the data from the disk the arm touches with the particular track and read the data from that location.

For locating a particular data from the disk the head moves around the disk very fastly and data which a user wants to access must have an address so that arm of the head just use that address means the number of cylinder, number of track and number of sectors from which user wants to read the data. With the help of these read and write heads we can also read the data from the disk and we can also stores some data onto the disk. Some time considerations are also used when we are accessing or storing the data onto the hard disk.

Working of hard disk:

A hard disk uses rigid rotating platters. Each platter has a planar magnetic surface on which digital data may be stored. Information is written to the disk by transmitting an electromagnetic flux through an read-write head that is very close to a magnetic material, which in turn changes its polarization due to the flux. A typical hard disk drive design consists of a central axis or spindle upon which the platters spin at a constant rotational velocity. The associated electronics control the movement of the read-write armature and the rotation of the disk, and perform reads and writes on demand from the disk controller. The sealed enclosure protects the drive internals from dust, condensation, and other sources of contamination. Contrary to popular belief, a hard disk drive does not contain a vacuum. Instead, the system relies on air pressure inside the drive to support the heads at their proper flying height while the disk is in motion.

1)     Seek time: -

The total time which is taken to move on the desired track is known as the seek time. And time is always measured by using the milliseconds.

2)     Latency time:

The time required to bring the particular track to the desired location means the total time to bring the correct the sector for reading or for the read and write head. This is also called as the average time.

3)     Data transfer time:

The total time which is required for reading and writing the data into the disk is known as the data transfer time.

3)    Floppy diskette:

Floppy disk is a kind of storage device that can be used to  carried around. The floppy disk is also a secondary storage device which is used for storing the data in a permanent manner.

Structure and data storage method

The floppy is made up of rigid mylar plastic and also contains a magnetic black disk inside the plastic cover. The floppy disk also stores all the data into the form of tracks and sectors and the floppy disk provides both reading and writing the data into the disk. For reading the data from the disk there are also some read and write heads.

Characteristics

The floppy disk is also called as reusable disk means the floppy disk provides us the facility to read and writes the data into disk as and when necessary and also many times. We can read and write the data from the disk.

The main advantage of the floppy disk is that the data can be stored many times but the main limitation of the floppy disk is that floppy disk have a small capacity and the  data stored into the disk may not be used for long time because the floppy disk is very sensitive thing when we move the head of the disk again and again then the floppy disk gets damaged. So that we can say that floppy disk is not a reliable thing. And on the other side the cost of floppy disk is also high comparison of the other storage media’s floppy.

The other advantage of the floppy disk is that floppy disk is used for moving the data from one computer to another and also put the disk into the another system for taking the data.

Types of floppy disks

There are two types of floppy disk available first is the 3.5 and second is the 5.2. But for inserting the floppy disk into the system we must have to use the floppy disk drive in the system. The capacity of the floppy disk is 1.44 MB.

Write protective quality

Floppy disk contains a notch which specify whether the data will be read or write means to say if we wants to protect our data then we can set the notch of the floppy disk as a read only.

Working of floppy disk: read data from the floppy disk:

The steps followed by the floppy disk drive to read data from the floppy disk: 1. The user executes a command, or disk. The program requests information from the floppy disk. 2. The spindle motor in the floppy disk drive rotates the floppy disk. 3. The stepper motor moves the read write head over the required track and the read write head reads the data from the floppy disk. 4. The floppy disk drive sends the data to the microprocessor for processing. 5. The spindle motor stops rotating the floppy disk in the floppy disk drive.

Write data on the floppy disk:

The steps followed by the floppy disk drive to write data on the floppy disk:

1. The user executes a command, or the program sends data to be written on the floppy disk.

2. The spindle motor in the floppy disk drive rotates the floppy disk.

3. The stepper motor moves the read write head over the required track for the read write head to read the track address from the floppy disk for storing the data.

4. The erase coils located on the read write head erases the data from the track.

5. The write head is wound up.

6. The write head converts the binary data into electromagnetic impulses and writes the data on the floppy disk.

7. The spindle motor stops rotating the floppy disk in the floppy disk drive.

4)    Optical disks:

The optical disks are also called as the cd-rom’s means compact disk read only memory which is also used for storing the data into the disk.

 

Structure and data storage method

This is called as the optical disk because the cd-rom’s are made up of the golden or aluminum material and the data is stored on the disk in the form of the tracks and sectors. The whole disk is divided into the number of tracks and the single track is divided into the number of sectors and the data is stored into the sectors and the disk is divided into the sectors as the first track contains the sectors in the huge size and the other tracks contains the sectors in a small manner. So that as the disk grows the disk is divided into the small number of tracks and the sectors.

Differentiate between hard disk and optical disk:

Hard Disk	Optical Disk
It is called as fixed disk	It is optical disk
Data is tored in concentric cirles	Data is stored in single spiral track
Computer takes less time to read from hard disk it is in range of 10 tp 30 miliseconds	Computer takes more time to read from cd-rom it is in range of 100 tp 300 miliseconds
Data can be read and write when required	It is permanent storage data once stored cannot  be erased hence it cannot be resued

Types of optical disk:

            There is two types of optical disk.

q  Cds

q  Dvds

Cds:

Cds is an optical disc used to store digital data. It was originally developed to store sound recordings only, but later it also allowed the protection of other types of data.

Dvd:

Dvd is an optical disc storage media format, and was invented in 1995. Its main uses are video and data storage. Dvds are of the same dimensions as compact discs (cds), but store more than six times as much data.

Introduction to Plants

Introduction to Plants:

Plants are critical to other life on this planet because they form the basis of all food webs. Most plants are auto trophic, creating their own food using water, carbon dioxide, and light through a process called photosynthesis. Some of the earliest fossils found have been aged at 3.8 billion years. These fossil deposits show evidence of photosynthesis, so plants, or the plant-like ancestors of plants, have lived on this planet longer that most other groups of organisms. At one time, anything that was green and that wasn’t an animal was considered to be a plant. Now, what were once considered “plants” are divided into several kingdoms: Protista, Fungi, and Plantae. Most aquatic plants occur in the kingdoms Plantae and Protista.
Photosynthesis - Page 1
6CO₂ + 12H₂O -----> C₆H₁₂O₆ (glucose) + 6H₂O + 6O₂ Photosynthesis is the process by which plants convert light, carbon dioxide and water into food, or energy. It is extremely important for the majority of life on earth because plants convert inorganic (unuseable) carbon into an organic (useable) form. Most of the carbon found on earth is in an inorganic form, such as carbon dioxide (CO₂), bicarbonate (HCO₃^-) and carbonate (CO₃^-2). Plants alter the carbon found in these compounds and store it as organic carbon compounds. Aquatic plants are especially important in this process because they account for 40% of the photosynthesis on the planet, though they are less than 1% of the plant biomass.