Storage Devices 2

Storage Devices 2

1. Primary memory

   • Also know as ROM and RAM
   • Backup
     • Copying of files/data to a different medium
       • Examples of Back up storage devices are : disks, tapes, flash drive, ect.)
     • Use incase of a problem with main secondary storage
   • Flash memory
     • A small storage device that uses nonvolatile semiconductor memory to store data on portable or remote computing devices
     • Examples of flash memory are: text, pictures, audio and video

2. Why is backing up data important?

   • To safeguard against loss of data due to the failure of original secondary storage device
   • To safeguard against damage caused by hackers
   • Incase the files need to be used elsewhere; this protect against possible corruption or loss
   • Corruption of files from damage by power surges

3. Types of access

   • Field
   • record
   • file

4. Serial access

   • In serial access it is necessary to start 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 to be updated and an additional tape is required called a transaction file.
       • The transaction file contains all new data to allow the master file to be updated
   • It is used in applications where speed of access or where order in which the data is accessed, isn't important
     • For example in utility billing, clearing banks cheques or producing pay slips.

5. Direct access

   • Direct access is used with magnetic disks, optical and solid state media.
   • It is much faster than with serial access
   • When files using direct access, old records
   • Not nessessary to sort records into any specific order first.
   • Direct access is used in applications where data access speed is vital

6. Secondary storage media

   • Secondary storage ensures that the data is stored permanently so that it can be used again at a later date.
   • Storage sizes or file sizes is typically measured in kilobytes (kB), megabytes (MB), gigabytes (GB) and terabytes (TB)
   • There are three different types of storage media: magnetic, optical and solid state
     • Magnetic Storage
       • Magnetic storage media depends on the magnetic properties of certain materials.
     • Fixed/Internal hard disk drive (HDD)
       • Fixed hard disk drives are the main method used for data storage
       • Uses
         • To store the operating system, systems software and working data/files.
         • Storing applications software that needs fast retrieval and storage of data
         • Used in real time systems (eg robots) and in online systems (eg booking airline tickets)
         • Used in file servers for computer networks
       • Advantages
         • They have a very fast data transfer rate and fast access times to data
         • They have a very large memory capacity
       • Disadvatages
         • Can be easily damaged if the correct shut down procedure is not carried out; this can lead to a crash which would result in a loss of data
         • They have many moving parts when compared to , for example solid state drives (SSDs)
         • Their read/write operation can be quite noisy compared to SSDs
     • Portable hard disk drives
       • Uses
         • They can be used as backup systems to prevent loss of data
         • They can be used to transfer data/files/software between computers
       • Advantages
         • The data access time and data transfer rate is very fast
         • They have a large memory capacity
         • They can be used as a method of transferring information between computers.
       • Disadvantages
         • They can easily damage if dropped or subjected to a strong magnetic field; as with fixed hard disk drives, an incorrect shut-down procedure could also lead to loss of data