4 GCSE OCR Computer Science - PowerPoint Presentation

Slide1

4

GCSEOCRComputer ScienceJ276

Storage

Unit 1

System architecture, memory and storage

Slide2

Describe flash memory Discuss the need for secondary storage including optical, magnetic and solid state storage Evaluate suitable storage devices and storage media for a given application using the following characteristics: capacity, speed, portability, durability, reliability, cost

Objectives

Slide3

Secondary storage

What do you already know about secondary storage and its role within computer systems?

MAIN MEMORY

SECONDARY

STORAGE

CENTRAL PROCESSING UNIT (CPU)

INPUT DEVICES

OUTPUT DEVICES

Slide4

Secondary storage

Are secondary storage devices volatile or non-volatile?

Why do we need secondary storage?

Why are there so many different types of secondary storage?

Slide5

Uses of secondary storage

Secondary storage is non-volatile – it keeps its content when the power is switched off

It has many different uses – for example:

Programs and data are stored on hard disk

CDs may be used to distribute software, music, e-books etc.

Memory sticks may be used to transport data from one place to another

Magnetic tape or external hard drives may be used for backup

What other uses are there for secondary storage devices?

Slide6

Storage types

Primary storage

RAM and ROM

Secondary storage

Hard Disk Drive (HDD)

Solid State Drive (SSD)

Offline secondary storage

Compact Disc (CD) or Digital Versatile Disc (DVD) or BluRay

USB Flash memory

Removable HDD

Magnetic tape

Slide7

Storage methods

Magnetic: Mechanical parts move over the disks surface to read and write data magneticallyOptical: Lasers read and write data using lightSolid State: Data is recorded onto solid memory chips without any moving parts

Slide8

Magnetic disks

Basic features:Disk contains concentric circles called tracksEach track is divided into sectorsDisk heads mounted on mechanical arms read and write the data

Slide9

Inside a hard disk

Slide10

Magnetic storage: hard drives

Fixed hard drives are built into virtually all PCs and laptopsThey have a very large storage capacity, up to 6TB or morePortable hard drives can be connected to a computer via a USB portThey are used for backing up or transporting dataSome portable music players have tiny hard drives no bigger than a small coinThey can store several GB of data

Slide11

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 - 6TB or greater

Slide12

Optical storage

Basic features:Data is stored as pits and lands burnt into a spiral track circulating outwards from the centreA laser beam passes over the pits and lands the level of reflection is measuredFrom this signal, 0s and 1s can be derived from reflections or no reflections

Slide13

How CDs work

Slide14

Optical storage

Advantages:

Cheap, very easily portable, takes up little space physically

Disadvantages:

Less storage capacity compared to other types

Easily damaged / scratched, requires a CD reader

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

Slide15

CDs, DVDs and BluRay

Why are the capacities of these discs different given they are all the same physical size?Microscopic view of the surface of a CD Rom

Slide16

Pit size and laser wavelength

Slide17

Solid State Drives (SSD)

Basic features:Solid-state disks use non-volatile flash memory to store informationVery fast burst read/write speeds due to data being physically close and easy to recoverNo mechanical or moving parts

Slide18

Solid State Drives

Uses:

Hand held computers Military usageCapacity:100GB – 16TB

Advantages:

Highly durable, no moving parts, very fast read/write speeds, no noisy fan, faster start up times

Disadvantages:

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

Slide19

Flash memory

Low cost, portable, no moving parts, durableThis makes them ideal for a range of offline devices:CamerasMobile phonesUSB memory sticks

Slide20

How flash memory works

Large electric current used to force electrons through a barrier and trap them on the other sideThey remain on the other side until “flashed” with a new current, hence the nameTrapped (charged) or not trapped = 0 or 1

Electrons trapped in this layer

Electrons detected here

Current applied and electrons forced through barrier

Barrier

Slide21

Cloud storage

Cloud storage refers to saving data in an off-site storage system maintained by a third party

Examples include example Dropbox and Google Drive

Instead of saving data on your computer's hard drive or other local storage device, you save it to a remote database, and access it via the Internet

What are the advantages in doing so?

Slide22

Worksheet

Complete

Task 1

on the worksheet

Slide23

Data capacity

Different storage devices have a range of storage capabilities

A higher capacity will allow greater data storage

How do you decide which storage device to use?

How do you calculate storage requirements?

Slide24

Data capacity

When you know how much data you need to store, you can decide which storage device(s) would be most appropriate

If you have 300GB of data to store, is optical storage appropriate?

If not, why not? What could you use instead?

Why is this particular device appropriate?

Slide25

Calculating data capacity

Knowing the capacity required will enable us to make an informed decision as to which device to use

If we have 500 files that are 300MB each, we need a total of 150GB

Which storage devices are suitable for this amount of data?

Slide26

Worksheet

Complete

Task 2 and 3

on the worksheet

Slide27