4. Storing and Retrieving
This involves saving data and information
and reloading it
Students are required to identify the
storage and retrieval processes at work in
an existing system e.g. a trip to the school
library or the administration office enable
these features to be identified
The administration office is also a good
venue to introduce students to data
backup and recovery, the importance of
which become evident ‘close to home’
5. Storing and Retrieving – Hardware
This there is a major emphasis on hardware and
the media used to store data/information
The syllabus suggests that students be given the
opportunity to use hardware devices (with
associated software)
Students need to be made aware that they do
this already
• Retrieval e.g. every time they activate a piece of
software or open a document it is being retrieved from
the computer hard disk (secondary storage) and then
loaded into memory (primary storage)
• Storage e.g. saving an open document to a USB drive or
burning a music CD
6. Storing and Retrieving – Hardware
Knowledge of the method used by each
type of media to represent data is
important
I show students a collection of old media
and storage devices, from the ‘relics’ box,
to show them how storage technology has
advanced over the years and discuss the
pros and cons of each
Also we categorise them using terms such
as magnetic, optical, physical, primary,
secondary, volatile, non-volatile, random,
sequential, etc (see below)
7. Storing and Retrieving – Hardware
One way storage can be classified in terms
of how data is accessed
Random (or direct) – data is able to be
accessed by read/write head moving to
the location on the medium where the
data is located e.g. this is the method
commonly used with magnetic disks
The location of each data item on the disk
is stored in a file allocation table (FAT) in a
reserved part of the disk
8. Storing and Retrieving – Hardware
Sequential – The read/write head starts
reading data at the beginning of the
medium and keeps reading until it finds
the required piece of data
This method is commonly used for tape
drives. These devices are still important,
because they are the most common
method used for backing up large volumes
of data
CDs also use one continuous spiral track
but songs can be accessed randomly
9. Storing and Retrieving – Hardware
Storage can also be classified in terms of its
permanence:
Volatile storage – is non permanent. It will
only store data for as long as electricity is
supplied to the device e.g. Random Access
Memory – RAM
Non-volatile – more permanent, will store
data for a long period of time without the
presence of electricity e.g. Hard Disk,
Diskette, USB drive, etc
10. Storing and Retrieving – Software
All storage devices need driver software to
enable the device to be integrated with
the rest of the system
Most drivers are included as a part of the
operating system
File management software enables data
files to be organised on some of the
storage devices attached to the computer
(like a hard disk)
11. Storing and Retrieving – Software
Databases are also another important
piece of software used to store data
FTP software is used to upload web page
files to a service provider (like the DET)
This is a good activity to do with students
as they enjoy seeing their work published
on the web but be aware of DET’s policies
on publishing material to the web
12. Non – Computer Tools
Students need to be aware that a
computer is not always the best
solution to a data storage problem
e.g. An address book is an efficient
means of storing data about friends
and relatives: non-volatile, random
access (if indexed), portable, no
hackers, no viruses, etc
14. Processing Data
At the macro level this process involves
the editing and updating of data
The importance of carrying out this task
are fairly obvious
At the micro level this process involves the
operation of the Central Processing Unit
(more later)
Students need to be able to distinguish
between: Centralised, Distributed and
Parallel processing
15. Centralised Processing
Dumb Terminal
(aka thin client)
– just a
keyboard and Server
screen
Data for processing is sent to server
Results of processing sent back for
display on the dumb terminal
16. Distributed Processing
Network
P.C.s – data is processed
using the local CPU
Server – performs
more complex
processing tasks
such as
authentication and
file storage
17. Parallel Processing
Large Task for Processing
CPU breaks large task into
smaller tasks
Small task 1 Small task 2 Small task 3 Small task 4
Multiple
CPU’s
process
each task
Result task 1 Result task 2 Result task 3 Result task 4
CPU combines the small results
to get an overall result
Result
18. The operation of the CPU
CPU – Central Processing Unit
The device that does all the “thinking”
Is made up of millions of microscopic
electrical components located on a single
silicon chip (aka microprocessor)
On larger systems the CPU can be
composed of many silicon chips
19. Components of the CPU
Control Unit – directs the flow of data
around the various components of the
computer.
Arithmetic Logic Unit (ALU) – carries
out arithmetic and logical operations,
basically doing additions very fast
Registers – small, temporary memory
locations used to hold the data and
instructions needed for processing
20. Operation of the CPU
The CPU processes data by using the
Fetch / Execute cycle
During i-time data/instructions are
fetched from memory and decoded
During e-time the ALU performs
operations on the data and stores
the result
21. Fetch Execute Cycle
Fetch Execute
or or
i-time e-time
Control Unit decodes ALU performs
the instruction (i.e. required operation on
What it has to do) data
Control Unit fetches Control Unit sends
next instruction from result back to RAM or
RAM and loads into a a register.
register.
22. Fetch Execute Cycle
Pipelining is a common method used to
speed up processors
In the past, each instruction went through
the entire fetch execute cycle before the
next instruction
With pipelining, when the CPU has sent
the first instruction for decoding, it also
fetches the second instruction
When the first instruction is being
executed by the ALU, the second
instruction is being decoded and the third
instruction is being fetched, etc
