S3: Storage

S3: Storage

1. Reasons for storing data

   • Files need to be stored to be used again
   • Data may need to be transferred from one computer to another
   • Backup copies are needed in case the original copies are lost or corrupted

2. File Compression

   • Reducing the size of a file by converting it to a different format
     • 1 MB = 1024 KB
     • 1 GB = 1024 MB
     • 1 TB = 1024 GB

3. Internal/External Storage

   • Backing storage stores data and program files within the computer
   • RAM (Random Access Memory) main memory where all locations can be read and written to equally quickly
   • ROM: Memory that cannot be changed; used to hold programs and data when the computer is being booted
   • BIOS: Basic Input/output System
   • Removable media: used to store data so that it can be taken away from the computer, such as floppy discs, CDs and flash memory

4. Magnetic Storage

   • Storing data on magnetised surfaces
   • Hard discs
     • Main storage device in a computer
     • Contains a number of metal platters which have been coated with a special magnetic material
       • The data is stored in this magnetic material. Thus, the hard disk is known as a magnetic storage device.
     • In order to access the data, the platters spin many thousands of times a second and a magnetic read and write head floats just above the surface of the platter.
     • Hard disks are measured in Gigabytes and Terabytes. Typical hard disks range from around 120 Gb - 3 Terabytes.
   • Floppy Discs
     • Store data on a circular piece of magnetic film, built into a plastic case for protection
     • Easily damaged & not reliable
     • Most computers do not come with a floppy disc drive anymore
     • Only hold 1.44 MB of data - no longer a practical storage method
   • DAT Tapes
     • Small in size but hold a lot of data
     • Often used to back up servers because they are easy to take away and store at a different location to the server
     • Slow to write to & very slow to retrieve data
     • Less reliable than hard drives and more difficult to restore selected files from
     • A useful removable backup medium

5. Optical storage

   • Use optical technology to etch the data onto a plastic-coated metal disc. Laser beams are then passed over the surface to read the data
     • CDs (Compact Discs) hold 650 MB
     • DVDs (Digital video discs) hold 4.7 GB
   • CD/DVD -ROMs are read only - often used to supply software
   • CD/DVD -Rs can have data written onto them once, & are then read only
   • CD/DVD -RWs can be read and written on many times

6. Flash Memory

   • Due to its small size, is used for portable devices such as mobile phones and digital cameras
   • Uses solid-state technology to store data on tiny cards of various types
   • Pen drives consist of flash memory built into a case with a USB connection, most operating systems will recognise and allow data to be transferred without installing drivers
     • Increasingly being used as the main storage medium in laptops & portable devices

7. Online Storage

   • Broadband internet connections increased upload and download speeds
     • More people able to store data away from their own computer