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

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.

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.

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)

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

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!!!

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

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.

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.

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

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

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

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?

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

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.

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.

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.