9th Class Computers Science Classification of Computer and Number System Storage Media

    Storage Media  

   Magnetic Tape

Magnetic tape is storage medium. Basically it consists of a thin tape with a coating of a fine magnetic material. It is used for recording analogue or digital data, such as audio video. Data is stored in frames and the frames are grouped into blocks which are separated from other blocks by some free spaces. Magnetic tape allows sequential technique for searching records. It similarly works like audio and video cassette. Storing data on tapes is considerably cheaper than storing data on disks. Accessing data on tapes, however, is much slower than accessing data on disks.

The following figure shows magnetic tape:  

  Hard Disk

The hard disk is another type of permanent storage media that is used to store huge volume of data. It is a reliable storage media. The storage capacity of hard disk is more than 160GB. A hard disk is physically composed of a series of flat, magnetically coated platters stacked on a spindle. A hard disk drive consists of numbers of inflexible magnetic disks mounted on a motor. These disks are spun by high speeds motors. The stored data of hard disk is read and written by read/write heads.  

  The internal structure of hard disk contains the following parts: 

• Read/Write Head : Is an interface between the magnetic disk and rest of the hard disk components. Basically it is used to read and write stored data from hard disk.
• Platters : Is a round magnetic disk coated by a thin layer of iron oxide. The size of the platter determines the size of the hard disk.
• Spindle Motor : Rotates the hard disk platters. It is very reliable because it rotates the disk platters without any damage.
• Electronic Circuit : Controls the hard disk and stores the data on the hard disk platters.
• Air Filters : Is used to remove the dust particles that may get into the hard disk.  

 There are four types of hard disk available in market. They are the following: 

• Advanced Technology Attachment (ATA) : Its data transfer speed between hard disk and system is up to 100 MB per second,
• Serial ATA : Its data transfer speed between hard disk and system is up to 600 MB per second. Redundant Array of Inexpensive Disk
• (RAID) : RAID technology combines more than one hard disk in an array. It is reliable data storage. If one hard disk fails the data can be retrieved easily.  

 Optical Disk

It is a storage medium from which Data is read and write by lasers. The storage capacity of optical disk is more than floppy. It stores data up to 6 gigabytes (6 billion bytes).  

 CD -ROM

It is a type of optical disk that is used to store data. It contains recorded data in digital form. The storage capacity of CD is about 650 megabytes. A CD can store huge amount of text, graphics, audio and video. The diameter of a standard CD is 120 mm. It stores up to 80 minutes of audio. The CD - ROM (Compact Disc Read - Only Memory) is ideal for distributing information, such as encyclopedias and other reference materials. There are two main types of CDs:  

• Compact Disc-R (CD - R): This type of CDs can be written only once and after writing they become read-only discs.
• Compact Disk - RW: This type of CDs allows over writing repeatedly by a computer, it can be written many times. You can erase the previous data and write the new content on the disc. The following figure shows CD.    

 In sequential access method records must be read in the same order as they were written to the storage media. Which one of the following storage media is used sequential access method?

(A) Floppy disk                                                 

(B) CD

(C) DVD                                                               

(D) Magnetic Tape

(E) None of these                

Answer: (D)                

Explanation                

Correct Option:

(D) The magnetic tape is an example of sequential access method.

Incorrect Options:

(A) Floppy is an example of direct access method.

(B) CD is an example of direct access method.

(C) DVD is an example of direct access method.    

 .................... is a round magnetic disk that is coated by a thin layer of iron oxide.

(A) Head                                                             

(B) Platters

(C) Spindle motor                                           

(D) Hard disk

(E) None of these  

Answer: (b)  

Explanation  

Correct Option:

Platters are a round magnetic disk that is coated by a thin layer of iron oxide.

Incorrect Options:

Rest of the options is incorrect.    

 The diameter of a standard CD is ........... mm.

(A) 100                                                                 

(B) 120

(C) 240                                                                 

(D) 140

(E) None of these  

Answer: (B)  

Explanation  

Correct Option:

The diameter of a standard CD is 120 mm.

Incorrect Options:

Rest of the options is incorrect.    

• The storage capacity of hard disk is more than 160GB.
• The diameter of a standard CD is 120 mm.    

• Mainframe Computer: The word length of mainframe computers may be 64 bits.
• Super Computer: The storage capacity of super computer is in pixabytes
• One's component: Is a system that is used to represent negative numbers.
• Direct Access Method: This method allows immediate direct access to individual records in a file. There are several techniques used to accomplish direct-access file organization.
• Optical Disk: Is a storage medium from which Data is read and written by lasers.     

• Micro Computer is a computer whose CPU (Central Processing Unit) is a microprocessor.
• The ICL39 and IBM 3090/4300 are the examples of mainframe computers. Supercomputers have limited use and limited market because they are very costly.
• One's component is a system that is used to represent negative numbers.
• A hard disk is physically composed of a series of flat, magnetically coated platters stacked on a spindle.
• CD is a type of optical disk that is used to store data.
• In 1974, Intel released the Intel 8080. It was the first usable microprocessor.
• The magnetic tape allows only sequential access to data.    

  Abbreviations

• ATA     ...................         Advanced Technology Attachments
• RAID    ...................         Redundant Array of Inexpensive Disk
• CRT      ...................         Cathode Ray Tube.