Storage Devices

Storage Devices

1. You need to save work safely

2. Storage capacity: data can either be stored in the 'internal memory' or on a 'storage device'.

3. Read Only Memory (ROM): stores the instructions which the computer uses when it 'boots-up' - BIOS (Basic Input Output System).

   • Can be read but not changed by user.
   • Attached to motherboard
   • Data is not erased when computer is switched off - stored permanently -> non volatile memory.

4. Random Access Memory (RAM): 'temporary memory' -> volatile memory.

   • Stores data you're working on and stores modules needed to make applications work.
   • Needed so you can have multiple windows open and switch between them.
   • If you have many windows/documents running it can slow system -> RAM is full -> can install extra RAM.

5. Hard disk: main storage device in computer. Stores data files and applications software.

   • Contains number of metal platters, coated with special magnetic material. (Magnetic storage device)
   • Platters spin to get info. Can come as stand-alone external drives.
   • Advantages: necessary to support computer, large storage capacity (120Gb - 3Tb), stores and retrieves data faster than others (DVD), stored items not lost when switched off, cheap cost per megabyte.
   • Disadvantages: slower to access data than RAM or ROM chips, can crash, regular crashes can damage surface of disk -> loss of data in that section, fixed inside so can't be easily transferred to another computer.

6. Magnetic Tape: (Large organisations use these)

   • Uses 'serial access' to find piece of data.
   • Advantages: relatively cheap per Mb of storage, can store large amounts (100Gb+), can be set up to do overnight/weekend, robotic archives/ backup systems can swap tapes automatically.
   • Disadvantages: serial access -> slow to access data, need special equipment to to record and read data on tape, less robust (can easily break).

7. Compact Disks (CDs): three main forms..

   • CD-ROM: data already stored i.e Music.
   • CD-WORM (Write Once Read Many): cannot save again.
   • CD-RW (ReWritable): save data over and over
   • Advantages: small, portable, cheap, most computers can read them, fairly fast to access data
   • Disadvantages: fragile, easy to snap/scratch, smaller storage capacity than DVD, slower to access than hard disk

8. Digital Versatile Disk (DVD): one of the most common methods of copying and backing up data at home.

   • 4.7Gb single sided, 9Gb double
   • Advantages: large storage capacity, sound/picture quality is excellent, mass produced -> cheap, DVD players can read CDs
   • Disadvantages: don't work in CD drives, no single standard, easily damaged

9. Flash Memory: small printed circuit board encased in plastic or metal casing. (1Gb+)

   • Advantages: compact, portable, hold more data than CD, reliable, easily branded, not affected by magnetic fields.
   • Disadvantages: more expensive than CD/DVD, easily lost, metal part (inserted into USB port) can be snapped off.

10. Blu-Ray: single layer 25Gb, double 50Gb.

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