• 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
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
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?
Storage Unit 1 Systems architecture, memory and storage
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?
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
Storage methods • 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
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
Magnetic storage: hard drives • Fixed hard drives are built into virtually all
PCs and laptops • They have a very large storage capacity, up to 6TB or more
• Portable hard drives can be connected to a computer via a USB port
• They are used for backing up or transporting data
• Some portable music players have tiny hard drives no bigger than a small coin
• They can store several GB of data
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
Solid State Drives (SSD) • 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
Storage Unit 1 Systems architecture, memory and storage
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
Storage Unit 1 Systems architecture, memory and storage
Advantages /disadvantages of SSDs
• Uses: • Portable computers • Military usage
• Capacity: • 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
Storage Unit 1 Systems architecture, memory and storage
Flash memory • Low cost, portable, no moving parts, durable
• This makes them ideal for a range of offline devices:
• Cameras
• Mobile phones
• USB memory sticks
Storage Unit 1 Systems architecture, memory and storage
Worksheet 4 • Complete Task 1 on the worksheet
Storage Unit 1 Systems architecture, memory and storage
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?
Storage Unit 1 Systems architecture, memory and storage
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?
Storage Unit 1 Systems architecture, memory and storage
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?
Storage Unit 1 Systems architecture, memory and storage
Worksheet 4 • Complete Task 2 and 3 on the worksheet
Storage Unit 1 Systems architecture, memory and storage
Plenary • Three different types of storage device have
been discussed
• Each has its own advantages for a particular application
• Technology is constantly moving forward, resulting in higher capacities, speeds and durability
• Prices are continually falling
Copyright
© 2016 PG Online Limited
The contents of this unit are protected by copyright.
This unit and all the worksheets, PowerPoint presentations, teaching guides and other associated files distributed with it are supplied to you by PG Online Limited under licence and may be used and copied by you only in accordance with the terms of the licence. Except as expressly permitted by the licence, no part of the materials distributed with this unit may be used, reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic or otherwise, without the prior written permission of PG Online Limited.
Licence agreement
This is a legal agreement between you, the end user, and PG Online Limited. This unit and all the worksheets, PowerPoint presentations, teaching guides and other associated files distributed with it is licensed, not sold, to you by PG Online Limited for use under the terms of the licence.
The materials distributed with this unit may be freely copied and used by members of a single institution on a single site only. You are not permitted to share in any way any of the materials or part of the materials with any third party, including users on another site or individuals who are members of a separate institution. You acknowledge that the materials must remain with you, the licencing institution, and no part of the materials may be transferred to another institution. You also agree not to procure, authorise, encourage, facilitate or enable any third party to reproduce these materials in whole or in part without the prior permission of PG Online Limited.
Storage Unit 1 Systems architecture, memory and storage
Top Related