L5 - Storage Devices

how does optical storage work?

• Available in read-only, recordable and rewritable

• Uses high powered laser to burn sections of the surface of the disc

• Low powered laser reads the disc by shining light onto the surface

• A sensor measures the light that is reflected back

• Pressed areas are pits, non-pressed areas are lands

• One single track, arranged as a tight spiral

advantages of optical storage

• Lightweight

• Portable

• Cheap to produce

• Can be easily distributed

• Good for storing films and music etc

disadvantages of optical storage

• Easily damaged/ scratched so data can be lost

• Low storage capacity

• Slow access and read-write speeds

how does magnetic storage work?

• Rigid rotating platters coated with magnetic material

• Ferrous particles are polarised to become north or south (0 or 1)

• Disk is divided into concentric circle tracks, which are divided into sectors

• Disks spin at up to 10000RPM

• Drive head moves across the disk to access different tracks and sectors

• May consist of several platters

advantages of magnetic storage

• Cheapest cost per MB

• High capacity

• Perform better when defragmented

• Fast read-write speeds

disadvantages of magnetic storage

• Least portable

• Has moving parts which will eventually fail

• Not very durable

how does solid state storage work?

• Contains an array of chips arranged on a board

• Comprises of millions of NAND flash memory cells, and a controller which manages pages and blocks of memory

• Each cell delivers a current to activate the flow of electrons

• When the current is turned off, some electrons are trapped in a floating gate transistor after being forced across an insulated oxide layer

• No electrons in floating gate=1, some electrons=0

advantages of solid state storage

• Fastest access speeds

• High capacity

• No moving parts so more durable

• Each piece of data can be accessed at the same speed because no drive head to move across the disk

• Consume less power, so cooler and less energy costs

• Less susceptible to damage

• Silent

• Lighter

• Portable

• No need to defragment

disadvantages of solid state

• Expensive

• Limited number of read-write cycles (?)

properties of RAM

• Volatile

• Contains the operating system, data and instructions currently being used by the CPU when it is running

• Read and write

• larger

properties of ROM

• Non-volatile

• Holds first instructions for when computer is switched on (the bootstrap)

• Read-only

• Smaller

• Can store programs in embedded systems

what is virtual storage (like logical vs physical storage stuff)

• Virtual storage is the abstraction of logical storage from physical storage

• Logical storage= a neatly structured and organised storage area under a single drive; this is what the user sees

• Physical storage= how the files are actually being stored; in reality the files could be stored across many different media such as magnetic disks, solid state drives, network servers and cloud storage

advantages of cloud storage

• Access at any time

• From any device

• Files no longer take up space in user’s own computer

• Automatic backups

• Can easily share and collaborate on files without having to use removable media

• From user’s pov, storage is limitless

disadvantages of cloud storage

• Can be expensive because monthly or yearly subscription cost

• No access to files without internet connection

• Security risk if data breach

• Uploading can take a while

• Slow access times if slow internet