Storage

Storage

1. Primary Storage

   • RAM
     • RAM stands for "random access memory".
     • Any point in the main memory can be directly accessed by RAM.
     • Volatile: data stored in the RAM is lost when the computer is turned off, so it must be stored in secondary storage if required again.
     • Used to store the operating system, graphical user interface (GUI) and applications.
   • ROM
     • ROM stands for "read-only memory".
     • It is non-volatile, meaning it retains its data when it isn't powered; the data it contains does not need to be written to secondary storage.
     • Stores BIOS (the instructions used to boot the computer).
   • Virtual Memory
     • Allows the hard disk to act as an extension of the RAM. It stores sections of data called pages in the hard disk when RAM space is running low.
     • Pages of data not being used by the RAM is moved to the hard disk, then moved back into the RAM when needed. This process is known as paging.
     • A disadvantage of virtual memory is that it takes much longer to access data than RAM.

2. Secondary Storage

   • Solid-State Drive (SSD)
     • Solid-state storage has no moving parts, making it more durable and faster than magnetic storage.
     • Expensive to manufacture.
     • Data can only be read from and written to a limited number of times, though this number is usually high - often in the hundreds of thousands or millions.
     • Can be made very small.
       • A disadvantage of this, however, is how easily the storage device can be misplaced; it would be difficult to misplace a large, heavy magnetic storage device such as a hard disk.
   • Three types: optical, solid state and magnetic.
   • Optical Storage
     • Extremely cheap to manufacture.
     • Fairly durable, allowing them to store data for long periods of time.
     • Storage quite limited compared to other media.
     • Examples: CDs, DVDs, Blu-ray discs.
     • Sometimes a special drive is required to read/write data from/to the disc, as is the case with Blu-ray.
   • Magnetic Storage
     • Can be damaged by magnetic fields.
     • Less durable due to moving parts.
     • Can read and write data quickly.
     • Quite cheap to manufacture.
     • Large storage capacity.