GCSEOCRComputingA451

Secondary storage

2-1-2 Computing hardware

3

Objectives• Describe common storage technologies such as optical,

magnetic and solid state

• Explain the need for secondary storage

• Select suitable storage devices and storage media for a given application and justify their choice using characteristics such as capacity, speed, portability, durability and reliability

Secondary storage

2-1-2 Computing hardware

Secondary Storage• What do you think is meant by the term Secondary

Storage?

Secondary storage

2-1-2 Computing hardware

Three main types of storage• Magnetic: Mechanical parts move over the disks

surface to read and write data magnetically

• Optical: Lasers read and write data using light

• Solid State: Data is recorded onto solid memory chips without any moving parts

Secondary storage

2-1-2 Computing hardware

Magnetic disks

Basic features:

• Disk contains concentric circles called tracks

• Each track is divided into sectors

• Disk heads mounted on mechanical arms read and write the data

Secondary storage

2-1-2 Computing hardware

Inside a hard disk

Secondary storage

2-1-2 Computing hardware

Magnetic Storage• Advantages:

• Cheap, vast storage capability, fast write speed• Disadvantages:

• Lots of mechanical parts, durability an issue, sealed unit due to disk head and platter precision and not very portable

• Uses: • Personal computers, storage of vast quantities of data

• Capacity: • 500GB - 3TB or greater

Secondary storage

2-1-2 Computing hardware

Optical Storage• Basic features:

• Data is stored as pits and lands burnt into a spiral track circulating outwards from the centre

• A laser beam passes over the pits and lands the level of reflection is measured

• From this signal, 0s and 1s can be derived from reflections or no reflections

Secondary storage

2-1-2 Computing hardware

How CDs work

Secondary storage

2-1-2 Computing hardware

Optical Storage• Advantages:

• Cheap, very easily portable, takes up little space physically• Disadvantages:

• Less storage capacity compared to other types• Easily damaged / scratched, must have the appropriate

reader device• Slow write speeds

• Uses:• Songs, videos and other multi-media storage, backup and

archiving of data• Capacity:

• CD-ROM – up to 720Mb• DVD– up to 8.4Gb• Blu-Ray – up to 50Gb

Secondary storage

2-1-2 Computing hardware

Solid State Storage• Basic features:

• Solid-state disks use non volatile flash memory to store information.

• Very fast burst read/write speeds due to data being physically close and easy to recover.

• No mechanical or moving parts

Secondary storage

2-1-2 Computing hardware

Solid State Storage

• Uses:• Personal hand held computers

(PDAs), Military Usage (robust all terrain laptops)

• Capacity:• 100GB – 750GB

• Advantages:• Highly durable, very fast read/write speeds, no noise, faster

start up times• Disadvantages:

• Expensive at present, less storage capacity / physical size than traditional hard disks

Secondary storage

2-1-2 Computing hardware

Flash memory• Low cost, portable, no moving parts, durable

• This makes them ideal for a range of devices:

• Cameras

• Mobile phones

• Portable computers

• USB memory sticks

Secondary storage

2-1-2 Computing hardware

How flash memory works• Large electric current used to force electrons

through a barrier and trap them on the other side

• They remain on the other side until “flashed” with a new current, hence the name

• Trapped (charged) or not trapped = 0 or 1

Electrons trapped in this layer

Electrons detected here

Current applied and electrons forced through barrier

Barrier

Secondary storage

2-1-2 Computing hardware

Worksheet 3• Secondary storage devices

• Use the ASCII Codes sheet to help you