Need is the mother of invention

DATA STORAGE IN PCS-


THERE R 2 TYPES OF  STORAGE DEVICES:-
1.PRIMARY STORAGE DEVICE
2.SECONDARY STORAGE DEVICES


1.PRIMARY STORAGE DEVICES:-
AS WE KNOW ABOUT RAM

RAM IS THE PRIMARY STORAGE DEVICE :-IT IS USED TO STORE TEMPORARY DATA  

WHICH IS AN ARITMETIC/LOGICAL OPERATION UNDERTAKEN BY THE PROCESSOR.IT  
ALSO BEING USED IN HANDLE THE CURRENT RUNNING PROCESS IN THE PROCESSOR

IT GIVES A HIGHER RESPONSE TIME TO THE COMPUTER TO PROCESS THE DATA IN  

PC. IT MAINLY REDUCES THE ACCESS TIME TO TO FAST UP THE COMPUTING SPEED.

 HERE WE HAVE THREE MAIN TYPES OF DEVICES IN THIS CATOGORY;-

1.PROCESSOR REGISTERS:-CONTAINS INTERMEDIATE RESULTS FROM THE 

  OPERATIONS PERFORMED BY PROCESSORS.Registers are the fastest of all forms of 

  computer data storage.




2.CACHE MEMORY:-DATA IS TRANSFERED FROM MAIN MEMORY TO CACHE 

MEMORY  TO IMPROVE THE SPEED AND PERFORMANCE.





3.MAIN MEMORY:-IT IS LOCATED OUT SIDE THE  PROCESSOR  AND CAN BE

ACCESSED FROM THE MAIN MEMORY AT A VERY HIGH SPEED.

 

  SECONDARY STORAGE DEVICE:-

 There r 2 types secondary storage device:-

1.Hard Disk

2.CD-ROM

 

1.HARD DRIVE:-

 

It is located inside the CPU.The first CPU built was having a capacity of 5MB and had fifty 24'' disks.It contains maganetic disks in side it.The disks mainly revolves to write the data in it.
But now a days size of the is being very small as compared to early days they occupy whole room but now we can fit it inside a laptop.

PHYSICAL STRUCTURE:- 

It contains one or more disks called platters.The platters r maganetized to hold data.It contains magnetic material that holds
data.All information  recorded on hard disk is recorded in tracks.
Each track is divided is into sectors.Sectors r the smallest adderssable unit in hard disk.One sector contains 512 bytes of data.

The topmost and bottommost surface are restained from containing any data.There r cylinders equal in number with tracks of each surface.It gives a conceptual idea of tracks that can be accessed without moving thing the read and write head.

STORAGE CAPACITY:- 

Hard disk is divided into cylinders.Cylinders r divided into tracks.Tracks are divided into sector.As u can see in the above figure.As we can see that data storage capacity depends on the
cylinder,sector and tracks.If any one these goes wrong than there will be problem in hard drive.
The simple formula for the above explanation is:-

HD capacity = No. of cylinders/disk*cylinder capacity
Cylinder capacity = no. of tracks*track capacity
Track capacity = no. of sectors*sector capacity

2.CD-ROM:-

 




   

CD-ROM is used to store data of any time type it does matter that
whether the data is analog or digital information that a computer can read and write.First the data in cd-rom can only read but in late 1990s the new type was introduced which can read and wirte both and data can be stored in the maganitic disks.There is lens which reads and writes the data in cd.It can store data upto 670MB in it.
Now a days there is a new technology DVD which can store upto 
3.70GB in it.
There is another tech. that can be like a small portable data transfering device it helps  in sending data in fast mode.It is known as pen drive.It can be of 4gb,8gb,16gb,32gb and 64gb.



 Structure of CD-ROM :-
Cd is made up of clear poly carbonate plastic and is protected by 
 clear lacqure.There r two basic ways of storing info. on disk 

1.Constant angular velocity(CAV):-
2.Constant linear  velocity(CLV):- 

 

Constant angular velocity(CAV)velocity:-In this disk moves at constant angular speed.It leads to the wastage of memory in CD
In this every sector isread in equal amount of time.Every sector stores different amount of data.Because of this there is wastage of data in the memory in the disk.

Constant linear velocity(CLV):-In this there is a constant linear speed of writing data in the disk.It saves the disk from wasting memory.The data is more densly packed in the inner levels.It covers the same length of areas both at inner and outer levels it moves with varying speed.CLV gives much better storage capability thats why it is used to read and write on CD.

Laser and optics

CD-ROM drives employ a near-infrared 780 nm laser diode. The 

laser beam is directed onto the disc via an opto-electronic tracking  

module, which then detects whether the beam has been reflected or 

scattered.

TRANSFER RATES

If a CD-ROM is read at the same rotational speed as an audio CD, the data transfer rate is 150 KiB/s, commonly referred to as "1×". At this data rate, the track moves along under the laser spot at about 1.2 m/s. To maintain this linear velocity as the optical head moves to different positions, the angular velocity is varied from 500 rpm at the inner edge to 200 rpm at the outer edge.

By increasing the speed at which the disc is spun, data can be 

transferred at greater rates. For example, a CD-ROM drive that can 

read at 8× speed spins the disc at 1600 to 4000 rpm, giving a linear 

velocity of 9.6 m/s and a transfer rate of 1200 KiB/s. Above 12× 

speed most drives read at Constant angular velocity (CAV, constant 

rpm) so that the motor is not made to change from one speed to 

another as the head seeks from place to place on the disc. In CAV 

mode the "×" number denotes the transfer rate at the outer edge of 

the disc, where it is a maximum. 20× was thought to be the 

maximum speed due to mechanical constraints 

until Samsung Electronics introduced the SCR-3230, a 32x 

CD-ROM drive which uses a ball bearing system to balance the

spinning disc in the drive to reduce vibration and noise.

As of 2004, the fastest transfer rate commonly available is about 

52× or 10,400 rpm and 7.62 MiB/s. Higher spin speeds are limited 

by the strength of the polycarbonate plastic of which the discs are 

made. At 52×, the linear velocity of the outermost part of the disk

around 65 m/s. However, improvements can still be obtained by 

the use of multiple laser pickups as demonstrated by 

the Kenwood TrueX 72× which uses seven laser beams and a 

rotation speed of approximately 10×.