Storage Devices and Media

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 • 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 • 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 • 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 • 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 • 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 • 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 - 1000 KB/s • CD-ROM - 100 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.