1.3 Storage

1.3 Storage

1. Primary Storage

   • Made up of RAM and ROM, this stores programs and instructions for the CPU to process

2. 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.
   • Need for secondary Storage
     • Permanently storing data and programs when they are not immediately needed by the computer.
     • Storing backups of data in case the originals are damaged or destroyed.
   • Types of secondary Storage
     • Optical
       • CD-ROM/CD-R, DVD-ROM/DVD-R, Bluray
       • Recordable optical media is cheap per GB although fewer devices have optical drives built in these days and DVDs and CDs have a smaller capacity than USB flash drives.
       • Optical discs are prone to scratching which can cause data loss and rewritable (RW) discs are particularly unreliable for long-term storage due to the stability of the chemicals that they are made from.
       • Optical discs offer faster access times than magnetic tape, but have slower transfer rates than Magnetic Hard Disk Drives and Flash Memory devices.
       • They are also small and very portable.
     • Magnetic
       • Hard Disks, Magnetic Tapes, old-fashioned floppy disks
       • Magnetic Hard Disks offer a large capacity for a relatively low cost-per-GB and they provide reasonably fast transfer rates (around 120MB/sec).
       • 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.
       • External Hard Disk Drives are often used for home and enterprise backup as they offer high capacity and low cost-per-GB whilst being portable and relatively quick for transferring large amounts of data.
     • Flash
       • Solid State Drives, USB memory sticks
       • Solid State Drives are made of flash memory, contain no moving parts and offer a much faster transfer rate than magnetic HDDs (around 550MB/s compared to 120MB/s for HDDs).
       • They offer good capacity (typically around 16GB to 64GB) for a reasonable cost-per-GB, though not as cheap-per-GB as Hard Disk Drives or optical media.
       • Flash memory has a higher cost-per-GB than Magnetic Hard Disks and can only be re-written a limited number of times, meaning that SSDs will start to degrade sooner than a Hard Disk would typically wear out, reducing their durability.
       • Good quality USB Flash Drives are also quite robust, surviving well in a bag or on a keyring, but they can suffer from damage if they are removed from devices prematurely, making them less reliable.
       • Their good capacity and cost, combined with being extremely portable makes them suitable for transferring documents and making short-term backups of files.
     • Capacity
     • Speed
     • Durability
     • Reliability
     • Portability