AS Level ICT

Selection and use of storage requirements, media, and devices:

Devices and media

Primary and Secondary storage

• The two means of storing programs and data in a computer system are:– Primary storage – this is storage that uses

chips within the control, arithmetic, and logic units

– Secondary storage – also know as backup storage, this is uses media that is outside the control, arithmetic, and logic units

Secondary storage

• Secondary storage is important because it allows users to:– Ensure that data is stored safely and securely so

that it can be accessible at a later date– Transfer data from one computer to another

Secondary storage

• There are a range of different devices that can be used as secondary storage including:– Magnetic disk drives– Optical drives– Magnetic tape drives– Solid-state storage (Flash/Pen drives and

Memory Card drives)

Magnetic disk drives

• Magnetic disk drives come in two different media:– Floppy drives – these use floppy disks– Hard drives (also known as Hard Disks)

Floppy drives

• Floppy disks are a removable media that fit into floppy drives

• The original floppy disk was produced in 1969 by IBM

• It was 8 inches across, and could store 80 kilobytes of data

• It was replaced in 1975 by the 5.25 inch floppy disk

Floppy drives

• These were, in turn, replaced in 1984 by the 3.5 inch floppy disk

• This is a flexible plastic disk, coated with a magnetic layer, within a hard plastic protective outer cover

A sliding metal cover protects the magnetised, plastic disk when it is not in the floppy disk drive

• Floppy disks originally held 360 kilobytes, but the latest versions can store 1.44 megabytes

Floppy drives

• Because the demands for large, portable storage media has grown considerably since the introduction of the 3.5 inch floppy disk, it is now reached the end of its life as a viable, large-scale storage media

• Many computers are now being sold without floppy drives and it is likely that it will soon become a museum piece like its predecessors

Hard drives

• Hard drives are also sometimes referred to as hard disks

• Hard drives consist of a series of rigid plastic disks, each of which is covered with a magnetic surface

• A hard disk spins at a speed of between 60 and 120 revolutions per second

• The data stored on the hard disk is read or written by a head that floats just above the disk (less than 0.1mm!) on a cushion of air

Hard drives

• Because the head is so close to the surface of the hard disk, even a dust particle can cause the head to ‘crash’ into the surface

• To stop this happening, hard disks are always kept inside sealed units

Hard drives

• The surface of a hard disk is divided up into Sectors and Tracks

• Data is stored in the ‘blocks’ created by the Sectors and Tracks

• Moving data into a ‘block’ is called Random Access

Hard drives

• Hard drives have the major advantages of having:– A very high transfer rate– A very large storage capacity

• Internal hard drives can also be added to existing computers in order to increase their storage capacity, and external hard drives – often connected via a USB – can be used as both additional storage and as a removable backup media

Optical drives

• Optical disks are a removable media that fit into optical drives

• They are flat circular disks that are covered with surface that can be ‘burned’ with a laser to create prismatic ‘bumps’

• The ‘bumps’ are used to store data• The ‘bumps’ can then be ‘read’ by a light beam that

reflects from the ‘bumps’• A read/write optical drive contains the laser that

‘burns’ the optical disk and the light beam that ‘reads’ it

Optical drives

• There are a variety of different optical disks available:– CD-ROM – Compact Disk – Read Only Memory– CD-R – Compact Disk - Recordable– CD-RW – Compact Disk - Rewriteable– DVD – Digital Versatile Disk– DVD-ROM – Digital Versatile Disk – Read Only

Memory– DVD+RW – Digital Versatile Disk + Read/Write

Compact disk – CD-ROM

• This is the most common type of CD available, and is the way in which most modern software is supplied to individual personal computers

• With CD-ROMs:– Data is read only– Data is stored as an optical pattern on the

surface of the disk– Storage capacity is 600 megabytes– Can used for the distribution of software

Compact disk – CD-R

• These are supplied ‘blank’ and can be ‘written to’ by CD-Writer drives

• They can be used to store large amounts of data, but once used, they can not be re-used

• They are ideal for use as a backup storage media or to store digital music

Compact disk – CD-RW

• These are supplied ‘blank’ and can be ‘written to’ by CD-Writer drives

• They can be used to store large amounts of data, and can be ‘written to’ many times, just like a hard drive

• However, the transfer rate is slower than that of a hard drive, and it is not as robust

Digital versatile disk

• The DVD was originally called the Digital Video Disk, but once it was realised how much data they could to store, the name was changed to reflect the disk’s versatility

• The DVD is now replacing the CD as the main method of bulk saving data on personal computers

• The reason for this is that they are capable of storing much larger amounts of data

• A DVD can store 17 gigabytes of data; this is equal to 26 CD-ROMs or 12,000 floppy disks!

Digital versatile disk – DVD-ROM

• These are mainly used for the distribution of movies

• DVD-ROM drives can read CD-ROMs

Digital versatile disk – DVD+RW

• These are supplied ‘blank’ and can be ‘written to’ by DVD-RW and DVD+RW drives

• The difference between the two types of rewriteable DVD is in the dye used on the surface of the DVD

• DVD-RW can be read by all DVD drives, but DVD+RW can only be read by the more modern DVD drives

Digital versatile disk – DVD+RW

• Older DVDs have a storage capacity of 4.7 gigabytes whereas the latest ones can store up to 8.5 gigabytes

Disk access time

• Disk access time is sometimes used to describe the speed at which different drives can access information.

• It is defined as the amount of time it takes for the drive’s head to reach the correct ‘block’ on a disk so that the data that has been selected can be accessed

• This can take up to 15 milliseconds for a hard disk and longer for other disk media

Magnetic tape drives

• Magnetic tape drives store data on plastic tape that is coated with a magnetic surface

• The tape is then stored on a reel or within a cartridge/cassette

• It is a cheap method of storing large amounts of data that does not need to be accessed quickly

• As a result, it is often used as a ‘backing store’ for large and mainframe computers

Magnetic tapes – Reel-to-reel

Reel-to-reel magnetic tape in use with a large or mainframe computer

Magnetic tapes – Cartridge/cassettes

A 400 gigabyte magnetic tape data cartridge or cassette

This would primarily be used a backup storage for a large or mainframe computer

Solid-state storage

• The use of solid-state storage devices (i.e. devices that use memory chips) in removable media has grown considerable over recent years

• The two most common solid-state storage devices in use are:– Flash/pen drives (also known as USB memory

sticks or thumb drives)– Memory cards

Flash/pen drives

• These have become very popular because they are cheap, portable, and have a reasonably large storage capacity (typically 1 to 8 gigabytes)

• They are a printed circuit board encased in a protective plastic case, and they interface with a computer via a USB connector

Flash/pen drives - Advantages

• The main advantages of flash/pen drives are:– They are small and lightweight– They can interface with any computer that has a

USB connector– They can store relatively large amounts of data– They are reliable as they have no moving parts

that can break– It is very difficult to damage data that is stored

on a flash/pen drive

Flash/pen drives - Disadvantages

• The main disadvantages of flash/pen drives are:– They can be easily lost or stolen– They have a slower transfer rate than a

magnetic hard drive

Memory cards

• These have become very popular as a storage media for use with digital cameras although they can be used to store any digital data

• They are a printed circuit board encased in a protective plastic case, and they interface with a camera or computer via a special connector

• They are very lightweight but must always be kept in a protective box when not in use as the special connectors can easily be damaged

Memory cards

• Examples of the different types of memory cards

• These include:– CompactFlash (CF Card)– Secure Digital Card (SD

Card)– MultiMediaCard (MMC)– Sony Memory Sticks– SmartMedia– xD-Picture Card

AS Level ICT

Selection and use of storage requirements, media, and devices:

Devices and media