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
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
