1.1.3
A LEVEL COMPUTER SCIENCE
1: Computer systems
INPUT, OUTPUT &
STORAGE
PART 2
STORAGE
•
1.1 Processors, I/O & Storage
•
1.1.1 Structure and function of
the processor
•
1.1.2 Types of processor
•
1.1.3 Input, output and storage
•
1.2 Software & development
•
1.3 Exchanging data
•
1.4 Data types, structures &
algorithms
•
1.5 Legal, moral, cultural & ethical
issues
2: Algorithms & Programming
•
2.1 Computational thinking
•
2.2 Problem solving & programming
•
2.3 Algorithms
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1.1.3 INPUT, OUTPUT AND STORAGE
a) How different input, output and storage
devices can be applied to the solution of
different problems.
b) The uses of magnetic, flash and optical
storage devices.
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IN THIS SECTION
ESSENTIAL
CHALLENGE
EXTEND
Give examples of the three types of
physical storage.
List advantages and disadvantages of
each type.
Argue the appropriateness of different
types for different users.
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Input, Output and Storage devices
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Magnetic, Flash and Optical storage
SECONDARY STORAGE
• Programs and data in use are stored in RAM
• However, RAM is volatile
• It loses its data when power is lost
• Secondary storage is non-volatile, it does not
lose data when there is no power
• Secondary storage is used to permanently store
both programs and data
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STORAGE TECHNOLOGIES
• Nowadays there are three main categories of storage
• Magnetic
• Optical
• SSD/Flash
• When choosing a storage technology we must take into
account three main factors (plus maybe a couple of others)
• Cost
• Speed
• Capacity
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MAGNETIC STORAGE
• Stores binary data
• Uses a disk or a reel of tape coated with magnetic material
• Polarisation represents data – North/South = 1/0
• Examples include:
• Hard Disk Drive (still common)
• Cassette Tapes (the music and video kinds is rare but
more robust versions are still commonly used for backup)
• Floppy Disk (very rare nowadays)
• Magnetic Core Memory (archaic, obsolete since 1975))
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MAGNETIC STORAGE - HARD DISK DRIVE
• Still the most common form of main storage for
home computers
• Typical capacity now is 500GB – 1TB (up to 6TB now
available commercially)
• Used to store:
• Operating System
• Applications
• Files (documents, music, videos, etc)
• Can be either internal or external (portable)
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MAGNETIC STORAGE - HARD DISK DRIVE
ADVANTAGES
• Very fast data access
• >1Mb/second
• Data can be read
directly from any part
of the hard disk
(Random Access)
DISADVANTAGES
• Moving parts and disks
that are vulnerable to
scratching
• Not suitable for mobile
devices
• Data very difficult to
recover if device fails
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OPTICAL STORAGE
• Stores binary data on a reflective surface
• Some areas reflect light, some don’t, representing 1 and 0
• Data read with a laser
• Examples include:
• CDs
• DVDs
• Blu-ray
• All of these are still common for media, though becoming
increasingly rare for computing, many laptops nowadays do
not even have an optical drive
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OPTICAL STORAGE
ADVANTAGES
• Hold a reasonable
amount of data
• CD – 800MB
• DVD – 4.7GB
• Blu-ray – 50GB
• Optical drives are
common and inexpensive
• Very portable
• Fast-ish data transfer rate
(about 88.5 Mb/s
depending on the drive)
DISADVANTAGES
• Data can be lost or corrupted
if the disc is scratched
• Memory capacity is not the
highest
• Cannot overwrite data (unless
using more expensive
versions with a more limited
life)
SOLID STATE DRIVES/FLASH MEMORY
• Stores binary data on semi-conductor material sheets
• Different areas act as switches that are either open (1)
or closed (0)
• Examples include:
• Solid State Drives
• USB sticks
• Compact flash cards (sometimes used in cameras)
• SSDs are used in much the same way as HDDs
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SOLID STATE DRIVES/FLASH MEMORY
ADVANTAGES:
• No moving parts – less
susceptible to physical shock
• Faster access time than HDD
• Not affected by magnets
• Lower power consumption
• No noise
DISADVANTAGES:
• Storage capacity less than hard
drives (though this is increasing
quickly)
• Data cannot be overwritten, it must
be deleted first – this leads to
slowdown with age
• Each switch has a limited number of
writes. This is large and optimisation
software means in home use it is not
much of an issue, but SSDs are not
very suitable to high-intensity
applications
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FUTURE OF STORAGE
• How have storage standards changed through
the years?
• What is the future of storage likely to be?
• At what point will we have “enough” storage?
Will we ever?
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FURTHER READING
P1 - Input Output Storage Activity 1 .pptx
P1 - Input Output Storage Activity 2.pptx
P2 - Storage Activity 1.pptx
P2 - Storage Activity 2.pptx
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