F451 full notes

Covers all specification points from the exam board. Fairly simple and concise.

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  • Created by: elliot
  • Created on: 13-05-11 17:43
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Computing F451
Hardware and software
o Hardware
Physical components of a computer system
o Software
Programs which provide a platform between the user and the
hardware, allowing the user to do something useful with the
o Input Device
A device which allows a user to tell the computer what to do,
or input data into a system.
Keyboard, Mouse, Microphone
o Storage Device
A device which stores user and data files, along with
instructions for the computer.
HDD, RAM, ROM, Flash drive, CD ROM, CDRW
o Output Device
A device which displays the result of computer commands in a
form that the user can understand
Monitor, Printer (Touch screen is both an input and
Software and systems development life cycle
o Problem Definition
Must be defined accurately or analyst will not know what
needs solving.
Defined by client
o Feasibility Study
To ensure that the problem can actually be solved.
Whether or not solution is possible
Is it economic or a better alternative than the current system?
o Information collection
Variety of ways to do this:
o + it gives a wide range of opinions
o - it has limited questions available
o - if there is a problem it cant be rectified easily
o + Like a conversation, difficult questions can be
o + Client's views expressed in detail
o - Does not give good idea of opinions of users
o + Allows analyst to see exactly where the errors
are in the old system
o - Does not give any views from client or users.

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Allows analyst to know what errors need to be rectified in the
new system
o Analysis
A specification is drawn up from the results of the problem
definition, feasibility study and information collection.
Outlines what the designer must take into consideration, and
what the aim of the system must be.
Is as exact as possible to ensure designer knows exactly what
needs to be done.…read more

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Spiral and Waterfall Models for systems life cycle
The above list of 9 stages works in a loop, once the new
system is being maintained a new problem may arise and the
lifecycle may begin again. However, if something goes horribly
wrong, let's say at the design stage we can't go back to other
stages to solve the problem. Spiral and waterfall models allow
any stage of the cycle to go backwards to any other stage.…read more

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E.g., workers registering at the start of the day,
or calculating the pay for workers, for their
hours worked.
Multi tasking, single user
o Allows one user to use the system at any one
o Allows multiple applications to run smoothly,
supposedly at the same time as each other
o E.g., A home PC. What you would use at home
for regular tasks.
o Links several computers together so that they
can share files and connections.
o E.g.…read more

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o Requires user to type in commands which the
system understands. User has access to entire
system but needs specialist knowledge to be
able to operate it properly.
Natural Language
o Computer understands human language.
Commands either typed into computer or
spoken to it are understood by the computer
and allow it to run. Very flawed due to
complexity of human language and very
processor intensive.…read more

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Uses base 2 (1's and 0's)
Because computers run on electrical signals which can either
be on (1) or off (0)
Bit = one 1/0
Nibble = 4 1/0's
Byte = 8 1/0's
Word can = 16 1/0's
Column headings are in base 2: ...128,64,32,16,8,4,2,1
Therefore the number 00000001 = 1 00000010 = 2 00000011 = 3
o Octal
Uses base 8
Column headings: ...…read more

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E.g. 01001011
Run through the above calculation, checking each column for
which of the 4 rules was used.
o Negative binary
Negative numbers can be represented in two ways. One uses a
sign of magnitude like our denary system. The column headings
become: +/-...64,32,16,8,4,2,1
So 10000001 = -1
The other method is preferable because every binary digit still
corresponds to a denary number.…read more

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MICR - Magnetic Ink Character Recognition is another method
of detecting ASCII characters. It works by detecting magnetic
traces in the ink (it is printed using special magnetic ink) and
interpreting the shape of the characters, once again converting
them into ASCII.
Barcodes are read by a laser scanner which senses the unique
width and distances between black bars on a white background.
These bars are able to represent a binary number, unique to a
specific product.…read more

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The Memory Address Register keeps a temporary storage of
where data has come from and where it is going to.
The Memory Data Register is where temporary data can be
stored to increase the speed of computer processes.
o PC
The Program Counter keeps track of the next instructions and
which order these should be carried out in.
The Current Instruction Register keeps track of the status of
the process currently being carried out.…read more

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Data that is not stored in the system memory is stored in
secondary storage
The HDD (Hard drive disk) is probably the main storage on a
computer. It can be used to store large amounts of user files,
however it is much slower to transfer data between it and the
Other forms of secondary storage can include:
CD-ROM, another form of read only memory that can
be stored on a disk.…read more


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