STORAGE

STORAGE

1. Types of storage in computer systems

   • Primary storage - made up of RAM and ROM, this stores programs and instructions for the CPU to process.
   • Secondary storage - permanently stores programs and data whilst they are not in use by the CPU. This is often provided by a Hard Disk Drive or Solid State Drive in a computer but can also take the form of removable media such as USB memory sticks and optical (CD/DVD) discs.

2. Secondary storage technologies

   • Magnetic storage ■ Hard Disks, Magnetic Tapes, old-fashioned floppy disks
   • Flash memory ■ Solid State Drives, USB memory sticks
   • Optical storage ■ CD-ROM/CD-R, DVD-ROM/DVD-R, Bluray

3. Magnetic Hard Disk Drives

   • The value of each bit of data (either 1 or 0) is represented as a positively or negatively charged magnetic particle on a magnetic disc (platter).
   • A magnetic read/write head is used to read and write data whilst the platter spins, typically at 5400, 7200 or 10000 revolutions per minute.
   • Magnetic Hard Disks are generally reliable - they keep working for a long time, however they will eventually develop faults due to wear and tear of the moving parts. They are also easily damaged if they are dropped or knocked when in operation, meaning that they are not very robust.
   • Hard Disks are often used as the main form of secondary storage in a computer system to hold the Operating System, applications and user data.

4. Storage capacity

   • The smallest unit of data that a computer can represent is a bit (b), it's value can be either 0 or 1.
   • A group of four bits is a nibble and a group of eight bits is a byte (B). ■ Because these units are very small, larger units are typically used to describe the size of data, including kilobytes (KB, 1KB = 1024 bytes), megabytes (MB, 1MB = 1024KB), gigabytes (GB, 1GB = 1024MB) and terabytes (1TB = 1024GB).
   • Note that each unit is 1024 times larger than the next smallest unit and not 1000 times. This is because 1024 is more easily represented in binary than 1000.

5. Optical storage

   • Optical storage technology uses laser light to retrieve data from the surface of optical media such as CDs and DVDsOptical storage technology uses laser light to retrieve data from the surface of optical media such as CDs and DVDs
   • Each 1 and 0 of the binary data is represented as microscopic holes (pits) on the surface of the disc.
   • A laser is then shone on the disc surface which either bounces back onto a sensor (if it hits a flat part of the surface) or it doesn't (if the laser hits a pit).
   • This "hit-or-miss" signal is used to reconstruct the 0s and 1s that make up the binary data.