gcse information technology storage devices and media objectives understand the difference between...

GCSE Information Technology

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 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 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

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 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

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

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.

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