# CPT4 Revision

CPT4 revision notes for AQA AS Computing.

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Version 3

CPT4: Binary and Binary Coded Decimal Revisited
Binary Representation:
The binary representation of 45 is:

128 64 32 16 8 4 2 1
0 0 1 0 1 1 0 1
Representation of a denary number to binary is done altogether by adding up to
create 45.

BCD…

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Version 3

Representation of Hex

In Books
In books, you can identify a hexadecimal as 5A3SIXTEEN or 5A3HEX.

In HTML
In HTML, you can identify hexadecimals as #FFFFFF where # identifies a

In C, C++, C#, Java and JavaScript
In these languages, a hexadecimal is shown with 0x. E.g.:…

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Version 3

CPT4: Representing Real Numbers

Fixed Point Real Numbers

There is an agreed position for the binary point. The numbers to the left of the
binary point are whole numbers.

8 7 6 5 4 3 2 1

The numbers to the right of the binary point are fractioned…

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Version 3

2.360 = 2.36 x103
0.001025 = 1.025 x103

The exponential tells you how many places the point moves.

There are different parts of a floatingpoint number: the Mantissa, the base
number and the exponential, which is a whole number and indicates how many
places the binary point moves.…

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Version 3

Step Two: As the exponential is positive, we move the binary point 3 places to
the right.
3 2 1 1/2 1/4 1/8 1/16 1/32
1 0 0 1 1 0 1 1

Step 3: The whole number represented is: 3

Step 4: The decimal is: 01325

Step…