In the case of magnetic tape the dots are arranged along the length of a long plastic strip which has been coated with a magnetisable layer (audio and video tapes use a similar technology).
In the case of magnetic discs (e.g. floppy disc or hard-drive), the dots are arranged in circles on the surface of a plastic, metal or glass disc that has a magnetisable coating.
Data is stored inside a hard-drive on rotating metal or glass discs (called ‘platters’).
Fixed Hard Drive
Fixed hard-drives act as the main backing storage device for almost all computers since they provide almost instant access to files (random access and high access speeds).
Portable Hard Drive
Portable hard-drives allow very large amounts of data to be transported from computer to computer.
Tapes are used where large amounts of data need to be stored, but where quick access to individual files is not required. A typical use is for data back-up (lots of data, but rarely only accessed in an emergency)
Tapes are also used and in some batch-processing applications (e.g. to hold the list of data that will be processed).
Removeable Media Magnetic Discs
Zip discs are random access devices which were used for data back-up or moving large files between computers.
Jaz discs are random access devices which were used for data back-up or moving large files between computers.
Like the Zip disc, this system never really caught on and was superseded by far cheaper and more reliable and cheaper technology.