Secondary Storage

Secondary Storage

1. Because main memory is volatile, a more long term means of storage is needed.

   • The most common secondary storage device is a computer's internal hard disk, which keeps programs and data stored even while the computer is turned off.
     • A computer's hard disk will usually be capable of storing more than main memory (often terabytes rather than gigabytes)

2. Magnetic Storage Devices

   • These include the internal hard disk as well as floppy disks
     • These disks are round and are divided into tracks and sectors
       • There are three tracks that are circular in shape and each track is divided into eight segments
         • The disk will spin to allow the disk's read write head to access the data in a particular segment
           • This will happen quickly with internal hard disks which spin at 7,200 rpm
             • An example of magnetic storage devices is an internal hard disk drive
               • 500 GB - 1 TB, data transfer from an internal drive is usually far quicker than any external device, not very portable, well protected by a sturdy case

3. Optical storage media

   • Optical storage media including CDs, DVDs & Blu-Ray disks, are written to and read from using lasers.
     • Optical disks spin to allow the laser to read the data from the correct location.
       • The surface of the disk will have billions of locations in which holes can be physically burned by a laser or not burned to represent either a 1 or a 0
         • An example of optical storage media is optical disks
           • 700 MB - 25 GB, speed is variable depending on type of disk (Blu-Ray drives are much quicker), Portable but not as portable as flash drives, quite sturdy although if the surface is scratched it can make data irretrievable

4. Solid-state storage devices

   • SSDs (of which flash drives are one type) use electronic circuits and no moving parts, to store data electronically.
     • With no moving parts, these devices are both sturdier and quieter than magnetic or optical devices.
       • An example of an SSD is a USB flash drive
         • 1GB - 64GB, transmits data very fast, very portable(small and light), very sturdy as it is an SSD
           • Commonly used by students who don't always work at the same computer but always need access to their work

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