Basics About Computer Storage Device

§  Storage Device :
-        The devices which stores our data permanently and when we need we can access that easily is known as Storage device.
-        Now days we are using Hard Disk for storing our data safely in our computer.

Here some storage devices which is describing below :

*       SASD (Serial Access Storage Device)
-        It stands for Serial Access Storage Device.
-        It stores data in continuous form so, that if we want to Access then we have to move that particular location where data is present in sequential manner.
-        Example :- If we are at first location of the storage and we want to move on tenth location then we have to move serially from one to tenth location to reach that data.
-        Best example of SASD is Magnetic tape.

*       DASD (Direct Access Data)
-        It stands for Direct Access Storage Device.
-        In this storage data is present in Hararical form on track and sector.
-        It can access data from any location without retrieving data from any other location. So, it can access randomly from any location.
-        Example :- Optical Disk, Magnetic Disk (HDD).

*       Magnetic tape
-        Magnetic Tape is a type of serial access storage device where data is stored serial.
-        It is made up of plastic ribbon where we will store data.
-        It’s widths is ½ or ¼ inches and length is 2 to 50 inches.
-        I’s uses magnetized material on the surface of plastic ribbon which is of Iron Oxide or Chromium Dioxide.
-        When any thing we want to write on magnetic tape then some spot is generated plastics ribbon where are data is stored.
-        The space between the plastic ribbon is known IRG (inter-recorded gap) and this gap is 0.5 inch.
-        Data transfer rate of magnetic tape is 7.7 MB per second.


*       Floppy Disk
-        Floppy Disk is made by IBM in 1971 or 1972.
-        It is made of Magnetized Circular Disk where Iron Oxide is present to protect this Disk plastic cover or Vin jacket is used.
-        There is a user label is present on plastic cover to write information abut what is present inside the Disk.
-        Inside floppy disk drive operature is present where the disk revolve and read write head will access the data present on that disk.
-        The data transfer rate of floppy disk is 10 to 30 bytes per second.
-        The rotation floppy disk is measures RPM (revolution per minute) and its revolution is 300 to 400 RPM.
-        Floppy Disk store data on both side.


§  3.5 inch Floppy Disk
-        It is latest floppy disk which can store a data on both side and according to different Architecture it can sour data in different size.
-        There are three sub category and 3.5 inch floppy disk.

                     i.          Double Density :-
-        In this floppy disk data on both side where 40 tracks, 18 sector per track and 512 byte per sector is available to store our data and it approx. 720 KB.
-        Example :-  2 * 40 tracks  *  18 sectors  / track * 512 byte / sector = 737280 bytes.

                   ii.          High Density :-
-        In this floppy disk data on both side where 40 tracks, 80 tracks, 18 sector / track and 512 byte / sector is available to store our data and it approx. 1.4 MB.
-        Example :-  2 * 80 * 512
                  = 1474560 byte.
                  = 1440 KB.
                  = 1.4 MB.
§  Mechanism of 3.5 inch Floppy Disk
-        When Floppy Disk is inserted into floppy disk drive then it start revolution and read-write head move to particular track and then to particular sector to read or write our data on the Disk.

*       Magnetic Disk
-        ­Magnetic Disk is a type of secondary storage device which can store data permanently.
-        Magnetic material is used on the surface of the disk which is of Iron Oxide.
-        It stores our data on a circular disk inform of track and sector.
-        The rotation speed of the disk is about 3600 RPM.
-        The disk plate are arranged o the central shaft and with the help of excess are read - write head moves horizontally to read or write our data on the disk.
-        On each disk plate data store on both side of the disk except upper outer disk lower outer disk.
-        Each disk side has one read write head but in some special cases it may be two read write head on a single disk t may be two read write head on a single disk surface to minimize the data transfer rate.






·        Seek Time :-
-        Seek time is the time taken by read write head to move from one position to specific track from where data will retrieve and the amount of time which is taken by this read write head to move on the particular track is know as Seek time.
-        Seek time is about 10 to 100 millisecond.
·        Latency
-        The read write head moves from track to particular sector where data is present, the amount of time taken by read write head to move from track to particular sector is known as Latency time.
-        Latency time is about 8.3 millisecond.
·        Data Transfer Rate
-        Control Signal send signal to particular read write head to access the data the read write head moves to the track and then to the sector and fetch the data from that sector and send it where it requires the total time taken by read write head to transfer the data is known as Data Transfer rate.
-        Data Transfer rate is about 3.8 MB/second.

Note :- The Gap between read write head and disk surface is about 0.00002 inch this gap prevent from damage of disk.