Secondary Storage

Secondary Memory Secondary memory or storage refers to non-volatile memory located externally from the computer. It is utilized for storing large amounts of data, offering permanent or long-term storage for data or programs, as well as serving as a backup storage solution. Various criteria can be used to classify secondary storage media: (i) Retrieval speed: […]

Secondary Memory

Secondary memory or storage refers to non-volatile memory located externally from the computer. It is utilized for storing large amounts of data, offering permanent or long-term storage for data or programs, as well as serving as a backup storage solution.

Various criteria can be used to classify secondary storage media:

(i) Retrieval speed: The time it takes to locate and retrieve stored data.

(ii) Size/Storage capacity: The ability to store data, with a preference for larger storage capacities.

(iii) Cost per bit of capacity: Preference for lower costs.

 

Types of Secondary Memory

(i) Magnetic Disk: A Mylar or metallic platter storing electronic data as tiny magnetic spots on its iron oxide coating. The access time is determined by seek time and search time. Transfer rate depends on data density and rotational speed.

 

Magnetic Disks are categorized

(a) Fixed disk or Hard disk: Made from materials like aluminum, with options for permanent installation or as removable disks.

 

Forms of Fixed disks or hard disks

  1. Larger permanent sealed metal disks (14-inch) for larger systems and minicomputers.
  2. Larger metal disks in removable cartridges (14-inch) for mini-sized and larger systems.
  3. Rigid disks permanently housed in Winchester drives, available in 9, 8, and 5¼-inch sizes.
  4. 3½-inch disks currently used in PCs, servers, and small notebooks.

 

(b) Floppy Disk: Available in three sizes – 8-inch portable floppy disk, 5¼-inch portable floppy disks, and compact floppy disks measuring less than 4 inches in diameter.

 

Optical Technology Storage

Involves the use of laser beams, highly concentrated beams of light, in the form of:

(a) Optical laser disks such as Compact Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW), Digital Versatile Disk (DVD), or flash. These can be read by CD-ROM drives, CD-RW drives, DVD-ROM drives, DVD-RW drives, and Flash drives.

(b) DVD Drive: Similar to CD but with a larger data capacity, made up of several layers of plastic totaling about 1.2 millimeters thick. Various types and formats are available, similar to CDs.

 

Flash Drives

These compact devices facilitate easy file transportation, with capacities ranging from 16 MB to 1 GB. Flash drives are faster and more reliable than floppy disks.

 

Comparison of Memory Devices

The characteristics of different data storage types in the storage hierarchy are summarized without the need for a table.

 

Differences Between Primary and Secondary Memory

Distinguishing Primary and Secondary Memory

Primary Storage Devices  Secondary Storage Devices

1          Characterized by temporary storage.   Characterized by permanent storage.

2          Typically more costly.        Typically more budget-friendly.

3          Notable for higher speed and, consequently, higher cost. Connected via cables, slower, and more economical.

4          Possesses lower storage capacity.         Boasts higher storage capacity.

5          Includes RAM, ROM, etc. Includes FDD, HDD, etc.

 

(a) BIT (Binary Digit): The smallest unit of information, representing either 0 or 1.

(b) NIBBLE: A grouping of four bits forming one nibble.

(c) BYTE: A fixed number of bits constituting a unit of information; a combination of 8 bits.

(d) CHARACTER: Represented by one byte, it can be a letter, digit, punctuation mark, or special character.

(e) WORD: Formed by the combination of 2, 4, or 8 bytes.

 

Data Measurement:

8 bits = 1 byte

1024 bytes = 1 kilobyte (KB)

1024 KB = 1 Megabyte (MB)

1024 MB = 1 Gigabyte (GB)

1024 GB = 1 Terabyte (TB)

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