Storage types and devices

Storage types and devices

1. 3.1 Backing up of data

   • Backing up refers to the copying of files/data to a different medium(disk, tape, flash drive, etc.)in case of a problem with the main secondary storage device.
     • Why back up data?
       • To safegaurd against loss of data due to the failure of the original secondary storage device
       • To safeguard against damage caused by hackers. This may not be their intention(they may only want to gain information for other purposes.
   • This chapter covers many forms of secondary storage and compares the advantages and disadvantages of each type.
   • In Chapter 1 you learnt about the primary memory, known as RAM and ROM. We will consider a number of storage devices later devices later but first it is important to consider why we need to back up data using thes devices and also how data is accessed.

2. Storage devices

   • HDD( Hard disk drive) - A drive with a disk that is placed in a computer and cannot be easily removed
   • Magnetic tape - tape used in recording sound, pictures, or computer data.
   • SSD( Solid state drive) -a nonvolatile storage device that stores persistent data on solid-state flash memory
   • CD/ DVD - a compact disc used as a read-only optical memory device for a computer system.

3. 3.2 Types of access

   • Serial access
     • When using serial access it is necessary to star at the beginning of the file and then access each record in turn until the required record is found.
     • It is primarily used on magnetic tape systems and is essentially a very slow form of data access.
       • When the original magnetic tape needs updating, an additional tape is required. The transaction file contains all the new data to allow the master file to be updated.
     • It is used in applications where speed of access, or where the order in which the data is accessed, isn't important.
   • Direct access
     • Direct access is used with magnetic disks, optical media and solid state media.
     • The computer uses the key field to calculate where data should be stored. It is then able to access the data directly from the calculated position.
     • Consequently, access is much faster than with serial access. when updating files using direct access, the old records/data are simply written over by the new records/ data. It is not necessary to sort records into any specific order first.
     • It is used in applications where data access speed is vital.

4. 3.3 Secondary Storage media

   • Dating right back to the advent of the personal computer, all systems have come equipped with some form of secondary storage
   • When a user loads data into a computer, the information is stored temporarily int the RAM - if the computer was turned off, this data would be lost.
   • Secondary storage devices ensure that data is stored permanently so that it can be used again at a later date
   • Throughout the chapter, you will notice that the term byte is used to measure the size of memory or storage.
   • Typically, storage sizes or file sizes are measured in kilobytes (KB), megabytes(MB), gigabytes(GB), and terabytes(TB)

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