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Storage and Media

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A computers RAM is volatile. This is why PCs have at least one type of backing store (also called secondary storage). In most PC's the main backing store device is the hard drive. This is where all of the users data and the installed programs stay when the computer is powered down. Hard discs are not the only type of backing storage the following is a list of storage media that you should know about.

Media Access

There are two ways in which data can be retrieved from storage media.

Serial Access

This applies to tapes. It means that to get data the reading device must start at the beginning of the tape and move through the tape in-order until the piece of data is found. This takes time and so serial access is normally slower than direct access.

Direct Access

This applies to disc media and solid state media. Direct access means that data can be retrieved from anywhere on the media without the need to move through in order.

Types of Storage Media

Magnetic storage Media

Floppy Disc Fixed Hard Disc
Portable Hard Disc Magnetic Tapes

Optical Storage Media


Solid State Storage Media

Memory Sticks & Pen Drives Flash Memory Cards

Floppy Disc

Floppy discs used to be the most common way of saving data so that it could be moved from one computer to another. They have the following features

  • 3.5 inches square in size
  • Capacity 1.44 Mb

Advantages and disadvantages

  • Portable
  • Cheaper than other types of storage media
  • Low capacity
  • Not compatible with most modern PCs

Fixed Hard Disc

These are the most common type of backing storage in modern PCs. They normally hold all of the installed programs and data for the PC while it is switched off.

Advantages and disadvantages

  • Not portable - fixed inside the computer
  • High capacity typically over 100 GB in modern laptops and more in desktops
  • Low cost per byte of storage capacity

Portable Hard Disc

Internally these are identical to fixed hard discs. The differences are

  • They have their own case to protect the drive
  • They normally connect via USB ports

Advantages and disadvantages

  • Portable
  • Large capacity often 100Gb or more
  • Easily damaged if dropped especially of they are switched on when they are dropped
  • Compatible with most modern PCs equiped with a USB port or similar

Magnetic Tape

These are not common in home or small business environments. They are popular in large companies with centralised computer facilities which require huge amounts of storage for backing up files. Mainframe computers will connect to many of these tapes on tape machines.

Advantages and disadvantages

  • Huge capcity up to 1 TB
  • Only allow serial access


These are both read-only optical storage discs. They are both 12cm in diameter. CD-ROMs can store about 700 MB while DVD-ROMs can store up to 17 GB

Advantages and disadvantages

  • Portable
  • Able to store large amounts of text, images and audio
  • Both are read only so cannot be used to store user data
  • DVD-ROMs can also store full length films

CD R and DVD R

These are both examples of 'Write-once Read Many' (WORM) optical storage media. They are purchased as blank media and can be written to with user data only once but then read from many times.

  • CD-R can store up to 650MB of data
  • DVD-R can hold 4.7GB of data

Advantages and disadvantages

  • Able to store user data
  • DVD-R are CD-R are compatible with traditional CD players after data has been written onto the disc


Compact Disk Rewritable & Digital Versatile Disc Rewritable.

Advantages and disadvantages

  • Can be written to multiple times so advantageous over WORM discs
  • May not be compatible with normal CD or DVD players


A competing technology to DVD-RW.

Blu Ray

Becoming the new format for movies and possibly replacing DVDs in the future. They use a blue laser to record more data onto a disc which is the same physical size as a DVD.

Advantages and disadvantages

  • Currently expensive compared to DVDs
  • Most computers don't have Blu ray players/ recorders as standard
  • Can store large amounts of data compared to DVDs, up to 50 GB for dual layered discs
  • Significantly more expensive than DVDs for consumer data storage.

Memory Sticks and Pen Drives

Use flash memory which is 'solid-state' meaning that it contains no moving parts (unlike disks which require drives with moving parts).

Advantages and disadvantages

  • Very portable even when compred to DVDs/CDs and 3.5" Disks
  • Fast access speeds for reading data
  • More resistant to damage from dropping etc.
  • More expensive per byte than hard discs
  • Packaged with a USB conector making them compatible with most modern PCs

Flash Memory Cards

Same technology as for memory sticks but packaged as cards of varying sizes and types. Common in cameras, handheld computers and modern mobile phones.

Advantages and Disagvantages

  • Multiple card formats means that it isn't as widely compatible as memory sticks (PC needs the right type of card slot)
  • Very small and so more easily lost
  • Very compact so more suitable for smaller devices than memory sticks