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Class notes Computing Cambridge IGCSE/GCSE Computer Science

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Unlock your potential with these comprehensive and concise Computer Science IGCSE Revision Notes. Covering the entire syllabus, these notes simplify complex topics for you - with well organized and structured notes - include illustrative diagrams, and focuses on main points for your exam. Perfect f...

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Computer Science IGCSE Revision Notes


1.1: Number Systems
The binary system is based on the number 2

Made up of 1s and 0s

Use of binary numbers in computer systems

Any form of data needs to be converted to binary to be processed/understood by the computer

Computer uses switches that function by turning on represented as ‘1’ and turning off represented as ‘0’

Data is processed using logic gates and stored in registers


Uses of Hexadecimal
Hexadecimal is a base 16 number system

Therefore, it needs to use 16 different ‘digits’ to represent each value

L.O: Identify uses of hexadecimal codes

Error codes are often shown as hexadecimal values

The numbers refer to the memory location of the error code




Computer Science IGCSE Revision Notes 1

, MAC Address:

Media Access Control (MAC) address refers to a number which uniquely identifies a device on a network

The MAC Address refers to the network interface card (NIC) which is part of the device

The MAC Address is rarely changed so that a particular device can always be identified no matter what it is



A MAC Address is usually made up of 48 bits which are shown as 6 groups of 2 hexadecimal digits

The first half (First 3 groups) is the identity number of the manufacturer of the device




Computer Science IGCSE Revision Notes 2

, The second half (Last 3 groups) is the serial number of the device



L.O: To describe IP address and its types

IP:

Each device connected to a network is given an address known as the Internet Protocol (IP) address



IPV4:

Number of bits: 32

Form: Hexadecimal and Denary



IPV6:

Number of bits: 128

Form: Hexadecimal




L.O: Describe features of HTML

HyperText Mark-up Language (HTML) is used when writing and developing web pages

Can write any feature (heading or smth)

HTML is often used to represent different colours of text on the computer screen




Computer Science IGCSE Revision Notes 3

, This means that different hexadecimal values represent different colours. For example:

# FF 00 00 represents primary colour red

# 00 FF 00 represent primary colour green

# 00 00 FF represents primary colour blue



Binary Addition Rules:
0+0=0
0+1=1
1+0=1
1 + 1 = 10



Addition of a binary number (Overflow condition):

The maximum denary of an 8-bit binary number is (2^8-1) = 255

The generation of a 9th bit number is a clear indication that it has exceeded its value

This is known as an overflow error and in this case is an indication that a number is too big to be stored in the
computer using 8 bits



You can use a larger number of bits to store very large values, for example, 16 bits is 65,536 maximum denary
value

Use of binary registers

Can be used to store data

Can be used to store instructions


Logical Binary Shifts
L.O: To solve problems using binary multiplication and logical binary shifts

The logical shift means moving the binary number to the left or to the right

Each shift left is equivalent to multiplying the binary number by 2

Each shift right is equivalent to dividing the binary number by 2

As bits are shifted, any empty positions are replaced with a zero



The denary number 21 is 00010101 in binary. If we put this into an 8-bit register:

If we now shift the bits in this register one place to the left, we obtain:

Notice how the empty right-most bit position is now filled with a 0

128 64 32 16 8 4 2 1

0 0 1 0 1 0 1 0


128 64 32 16 8 4 2 1

0 0 0 1 0 1 0 1

The left-most bit is often referred to as the MOST SIGNIFICANT BIT, and now here, the left-most bit is now lost
following a left shift

If the left-most 1-bit has been lost in the 8-bit register, this error is because we have exceeded the maximum
number of left shifts possible using this register

The value of the binary bits is now 21 x 2^1 (41). Similarly if you shift the original number two places, 21 x 2^2 (41 x
2)




Computer Science IGCSE Revision Notes 4

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