Primary & Secondary Storage

Primary & Secondary Storage

1. Secondary storage- any storage that is not directly controlled by them CPU, e.g. CD or hard drive

   • Needed to store data long-term as RAM is volatile

2. Optical storage e.g. CD, DVD, Blu-ray

   • Uses a lens and a light beam to read/write data onto a disk
   • Portable- small and light
   • Cheap to manufacture
   • Fairly durable- safe to store data on for long periods of time
   • Some formats (e.g. CD-R and DVD-R) mean that data cannot be overwritten
   • Storage capacity is relatively small compared to other storage devices- CDs can typically hold up to 700mb of data
   • For some (e.g. Blu-ray) a special drive is needed to read/write the data to/from a disk

3. Magnetic storage e.g. hard disk drive

   • Uses magnets to record data on rotating metal plates
   • Large storage capacity
   • Fast access to read/write data
   • Fairly cheap to manufacture
   • Data can be lost/altered by magnetic field or mechanical problems
   • Can suffer wear and tear due to moving parts

4. Solid-state storage e.g. SD cards, USB memory sticks

   • Uses flash memories to store data
   • Faster boot-up- they have no moving parts so they don't have to 'warm up'
   • Can be made very compact in size
   • Large storage capacity
   • More robust (unlikely to break) than magnetic- has no moving parts
   • Expensive to manufacture
   • Has a limited amount of time data can be written to/read from (although this can be thousands or even millions)

5. What elements can we consider when choosing a suitable storage device?

   • Capacity- the amount of data we can store on the device
   • Speed- the rate at which it can transfer data
   • Portability- the device is easy to carry and move around
   • Durability- the length of time the device can store data without failing or becoming damaged
   • Reliability- whether data is stored without technical errors and is still reliable
   • Cost- the cost of manufacture for a device

6. RAM= Random Access Memory

   • Stores all data and programs currently in use
   • Volatile- if the computer is turned off, the data is lost
   • Quicker to read/write to than other storage in computers
   • We need a hard drive to save data on so the computer can be turned off
   • Locations in the memory can be directly accessed

7. ROM= Read-Only Memory

   • Computer only reads from this memory- it doesn't write to it
   • It contains the programs needed to 'boot-up' your computer
   • Non-volatile- the data is saved even after your computer is switched off
   • Very small amount of memory

8. What is virtual memory?

   • Allows the hard disk to act as an extension of the RAM
   • Unused programs are moved to free up space
   • Used when the RAM is full