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2.4 Flash Memory

Flash memory is a small chip memory which is a type of EEPROM. It can store data in the form of video, images and other format. The stored data can be read and deleted to store new one. The deletion of data is carried by high speed current of device.

Hard Disk
Fig. Structure of Hard Disk
Hard disk is a secondary memory or storage device which can store large amount of data which can be stored for long time period without need of any power backup. A hard disk is used to store operating system, programs data and information.

A hard disk consists of a almunium disk which is fixed on a DC motor known as spindle motor. The disk plate known as platter is coated with magnetic oxide material and covered by shining material. The disk plate consists of number of circular tracks on both side of the plate. The section of track is known as sector and group of sector is known as cluster. The data is actually stores in a sector.  

A single platter consists of two read/write heads one for upper surface and other for lower surface. The read/write is a small circuit which is placed above disk surface at a distance of few millimeter. The read/write is controlled by Head Actuator. 

The reading/writing process is carried out by read/write head on the platter. When any data or information is to be stored, it reaches to hard disk circuit as 1 and 0, then DSP chip converts it into electrical pulses which is sent to read/write head. The read/write head which is small circuit places data in the form of magnetic charge on track. The magnetic charge can be North-south or South-north as per 1 and 0. When stored charge is read it is change into electrical pulses and back into 1 and 0 by DSP.