1. Storage Devices and Media
Objectives
Understand the difference between internal memory & backing storage
Be able to identify different types of storage devices & media
Identify the uses, advantages & disadvantages of different types of storage devices & media

2. Difference between internal memory & backing storage
Internal memory is the memory that is occupied by the current data and instruction being dealt with.
Its contents are lost when the computer is turned off.
Backing storage is the additional memory which is used to store data & instructions that we may need to use again.
Hard Disk & Drive
Floppy Disk & Drive
Optical Disk Drive
USB Storage Devices
Magnetic Tape
Its contents are NOT lost when the computer is turned off.

3. Difference between internal memory & backing storage
Internal memory, also known as Immediate Access Storage (IAS) is:
Small
Fast
Volatile
Backing storage is:
Large
Non –Volatile
Not very fast to read from.

4. How do we measure the size of memory?
Storing an individual character such as a letter, number or other character needs a set amount of space called a
Byte
To store 1024 characters we need 1024 Bytes or 1Kilobyte (1Kb)
1 million bytes (or 1000Kb) is called I Megabyte (Mb)
1000 Mb is called 1 Gigabyte (1Gb)

5. Hard disk drives
The Hard Drive is the DEVICE which reads & writes to the Hard Disk
The Hard Disk is the STORAGE MEDIA
It’s Magnetic media
Data is stored magnetically onto tracks on the disk
Disk rotates at high speed – passing under the read/write heads
Read/write heads READ the data into main memory and WRITE data back to the disk after it has been dealt with

6. Hard disk drives Uses Advantages Disadvantages Stores software
Stores your data files
Advantages
Large storage capacity
Stored items are not lost when the computer is switched off.
Usually fixed inside the computer, so can’t get lost.
Disadvantages
Slower than IAS
If the hard disk crashes the computer will not work & you have lost your work!!!

7. Floppy disks & drives Uses Advantages Disadvantages
To keep personal data
Keep extra copies of data
Advantages
Can be carried with you
Disadvantages
Limited capacity (typically 1.44Mb)
Unlikely to store your ICT coursework on one disk

8. Zip Drives
Zip drives are similar to floppy drives because the individual disks are removable and portable but they hold much larger amounts of data
Typically between 100 MB and 2 GB.

9. Optical disk drives CD Rom Uses Advantages Disadvantages
Compact Disk Read Only Memory
Known as WORM devices Write Once Read Many times.
Uses
Storing software
Reference material (multimedia)
Advantages
Data cannot be erased
Portable
Much larger capacity than floppy disks (about 650Mb)
Disadvantages
Can get lost
Can’t write data to a CD Rom
Data access can be slower than a hard drive.

10. Optical disk drives DVD Uses Advantages Disadvantages
Digital Versatile Disk
Uses
Storing high quality audio & video
Advantages
Data cannot be erased
Portable
Much larger capacity than floppy disks and CD Rom (about 4.7 Gb)
Disadvantages
Can get lost
Can’t write data to a standard DVD

11. Optical disk drives CD Rewriter Uses Advantages Disadvantages
Back up software & data files
Copy music files
Advantages
Portable
Can store much larger files than floppy disks
Disadvantages
Can get lost
Can’t always be read in some Optical drives

12. Optical disk drives DVD Rewriter Uses Advantages Disadvantages
Back up software & data files
Copy video files
Advantages
Portable
Can store much larger files than CD R’s
Disadvantages
Can get lost
Can’t always be read in some Optical drives or DVD players

13. USB storage devices Recent development Fits on a key ring
Smallest storage capacity is about 32Mb = about 22 floppy disks
1Gb versions now available
Is this the end of the floppy disk?

14. Comparing storage device capacity:
1 CD-ROM (650 MB) = 451 Floppy disks (1.44 MB)
1 DVD (4.7 GB) = 7 CD-ROM's (650 MB)
Access speed
Hard drive KB/s
CD-ROM KB/s
Floppy disk - 36 KB/s

15. Storage used for back-ups
Magnetic tape
Comes in two forms; tape reels, and cassettes or cartridges.
Large tape reels are used to make backup copies of programs and data on large mainframe computers.
Cartridges are used to make backup copies of the programs and data on personal computers and networks.
The main advantage of using magnetic tape as backing storage is that it is relatively cheap and can store large amounts of data.

16. Direct and serial access
Floppy disks, hard disks CDs and USB storage devices all allow direct access to data.
Direct access means that the required data can be found straight away without having to read through all the data on the disk.
Magnetic tape allows only serial access to data. To locate data on a magnetic tape it has to be searched from the beginning until the required data is found.

17. File compression
File compression software can be used to make files smaller so that more data can be stored in the same amount of space on backing store.
When a compressed file on backing store needs to be used it must be decompressed.
This can be done using decompression software or by setting files up to be self-extracting which means that they can automatically decompress themselves.
Winzip is an example of software that can be used to compress and decompress files.