Secondary Storage

Secondary Storage

1. Computers are able to process input data and output the results of that processing, but it would be difficult if we had to keep re-entering all the data and programs every time we wanted to use the computer.

   • Secondary storage is used to store data and programs when the power is switched off
   • RAM is volatile so the contents are lost if the power is switched off; ROM can only store pre-programmed data and programs.

2. Magnetic hard disk

   • Currently the most common type of secondary storage with very large capacities and good access speed.
     • Advantages: Is reliable; has a high capacity at low cost; can be an internal device or external portable device for backup or transfer of large amounts of data; stores the operating system, user data and programs.
       • Disadvantages: Can crash causing the computer to stop working, if it crashes the data stored on the disk can be lost from the damage, the disk is fixed in the computer meaning it is hard to transfer data from it to another computer.

3. Optical Disk

   • -CD (compact disk) or DVD (digital versatile disk) -can be read only or read / write CD/DVD ROM -used to distribute programs CD/DVD R/W -used to store, transfer or backup data and programs.
     • Advantages: high capacity at low cost, small and easy to distribute, robust and can be used many times, CD 700MB, DVD 4.7GB typical capacity
       • Disadvantages: slower than other media such as hard disk and flash ROM, Optical disks require a more complicated drive mechanism than magnetic disks, Easily broken, they require special drive to read and write, It is expensive

4. Flash (solid state) memory

   • Electronically alterable Read Only Memory used in portable devices such as cameras, MP3 players, tablet computers and mobile phones used with a USB interface as a backup / transfer medium for personal files
     • Advantages: fast access times, reliable with no moving parts to go wrong, low power use, small, light, robust and highly portable, inexpensive at relatively low capacities
       • Disadvantages: Easy to lose, anyone can access your files if the memory stick is lost, expensive at higher capacities.

5. When choosing which type of secondary storage to use, you need to consider:

   • Capacity – how much data does it need to hold? Speed – how quickly can data be transferred? Portability – does it need to be portable or used to move data from one system to another? Durability – is it easily damaged? Reliability – is it subject to deterioration over time or with repeated use?