INFO 1 Data Storage

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Storage Capacity

Storage capacities and file sizes are measured (from lowest to highest) in:

  • Bits
  • Bytes
  • Kilobytes
  • Megabytes
  • Gigabytes
  • Terabytes
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Read Only Memory

ROM is a special kind of momery which stores the instructions which the computer uses when it "boots up" - the BIOS (Basic Input Output System) 

It allows it to check the type of hard disk installed eg. the amount of RAM installed, because the data is read only it can be read but not changed by the user

ROM the data is not erased when the computer is switched off - the data is stored permanently 

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Random Access Memory

RAM is a fast temporary type of memory in which programs, applications and data are stored. here are some examples of what's stored in RAM:

  • The operating system
  • Applications
  • The graphical user interface

If a computer loses power, all data stored in its RAM is lost 

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Hard Disk

The hard disk is the main storage device in your computer. All your data files and applications software are stored on it.

The hard disk contains a number of metal platters which have been coated with a special magnetic material. The data is stored on this magnetic material. In order to access the data the platter spins many thousands of times a second and a magnetic read and write head floats just above the surface of the platter

This is in most computers and can store all the data forever. It is readable and can be edited and deleted. Hard disks are measured in gigabytes and terabytes. Typical hard disks range from 120 Gb - 3 Terabytes

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Hard Disk


  • Necessary to support the way your computer works
  • Large storage capacity
  • Stores and retrieve data much faster
  • Stored items are not lost when you switch off the computer
  • Cheap on a cost per megabyte compared to the other storage devices 


  • Far slower to access data than RAM or ROM
  • Hard disks can crash which stops the computer from working
  • Regular crashes can damage the surface of the disk, leading to loss of data in that sector
  • the disk is fixed inside the computer and can not be easily transferred to another computer 
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Magnetic Tape

Magentic Tape uses Serial Access to find a piece of data. To find the data you have to start at the beginnning of the tape and continue fast forwarding until you get to the piece of data that you need this makes it slow.


  • Cheap per megabyte storage
  • Can store large amounts of data
  • Can be set up to do the back up overnight or over the weekend
  • Robotic archieve and backup system can swap tapes in and out automatically


  • Serial access so can be quite slow to access data
  • need a special peice of equipment to record and read the data on the tape
  • less robust than other media as the tape can easily break
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Compact Disks

CDs are known as optical storage devices. Data is burned onto the surface of the disk using a laser beam in the CD Drive. A laser bean is also used to read the stored data. 650 Mb of data. Three main forms:

CD-ROM - CD Read Only Memory. this means that when you buy the disk, it already has the data or program stored on it. You can read it, but can't save it. An example would be a music CD that you buy from a store.

CD-WORM - CD Write Once Read Many. This means that you are able to save to this disk one timem so you can store your data or an apllication on it of your choice. however once you have saved onton the disk once you can access the data many times but cant save onto it again. 

CD-RW - CD Rewritable. This means that you can save data to your disk over and over again, like a floppy disk.


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Compact Disk


  • Small and portable
  • Very cheap to produce
  • Most computers can read CD's
  • Fast to access the data


  • Fragile easy to snap or scratch
  • Smaller storage capacity than a hard drive
  • Slower to access than the hard drive
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Digital Versatile Disk

DVD's are most common method of copying and backing up data at home. Is similar to a CD in which it is an Optical Device and that a laser used to store the data and read it. Can store 4.7Gb of data, some can hold data on both sides which holds 9Gb of data.


  • Very large storage capacity
  • Sound and picture is excellent 
  • DVDs are now mass produced so they are cheap 
  • DVD players can read CDs


  • DVDs don't work in CD drives
  • There is no single standards of DVD 
  • They can be easily damaged by breaking or scratching
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DVD-ROMs - read only, the data is written to them before they are sold

DVD-R meaning DVD-Recordable, the user can write data to the DVD once or fill it over time using multi-session

DVD-RW meaning DVD-Rewritable, the DVD can be written and re-written to. Unlike multi-session discs, existing data be overwritten

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Flash Memory

Small, lightweight, removable and rewritable. They consitst of a small printed circuit board which is encased in plastic or metal casing. They usually have a removable cap which covers and protects the part of the stick which is inserted into a USB Port.

Are avaliable from 1 Gb up


  • They are more compact and portable 
  • Hold more data than a CD
  • They are reliable as they have removable parts
  • They are easily branded on their covers to reflect organisations


  • More expensive than CD
  • They can be easily lost
  • The mental part which inserted into the USB port can be snapped off or damaged 
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Memory Card

A memory card is a stamp-sized UBD device and can be used in a similar way ro a floppy disk but it is inserted into either a memory card reader or a USB converter - it is then seen by the computer as a removable drive. They are typically come in sizes from 1 Gb to 32 Gb upwards, depending on the price paid. There are many avilable memory card formats, but since 2010 the SD card became the more favoured format.


  • Memory card can hold large quantities of data
  • They are extremely portable so the user can take them wherever they go
  • Digital acccessories such as compact cameras and moblie phones are able to read and write the memory cards allowing the user to transport large collections of photos, songs or information with them. 
  • They are durable because they have no moving parts


  • Memory cards, specifically the micro SD card, are the smallest storage device available. This means they are more likely to be lost, stolen or damaged
  • All computers do not come with memory card reader built in. Users will often be required to purchase a card reader or UBS converter to view the data on the card
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Blu-Ray disk can store even more data than a DVD. They can hold 25Gb to 50Gb. looks similar to a DVd however only dedicated Blu-Ray players can play them. They are mainly used to store HD movies. The name comes from the fact that the players use a blue laser instead of a red to read and write the data.


  • They store much more data than a DVD disk
  • They are able to store a full length Hd film


  • You need a dedicated Blu-Ray playyer to play the disk
  • Loading a film can take minutes as so much data needs to be read 
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Floppy Disk

Computer need a floppy drive to read a floppy disk and many modern computers are no longer supplied with a floppy disk drive because we no work with much larger files. In the past, floppy disks were used to:

  • Transfer small files of data from one machine to another
  • Backup important small files that are stored on your hard disk
  • Store restricted files that you dont want other users of your computer seeing. 
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