IGCSE COMPUTER SCIENCE
1. Data Representation
1.1 Binary systems
● Binary data
○ Computer
■ Electronic machine to process data
■ Data → Process → Information
○ Processor
■ Stores data using electrical switches (on/off)
■ Stores & processes data
○ Binary
■ Base 2 (on/off)
■ All data must be turned into binary for computer to process
es
■ Used for registers where a certain bit controls a specific thing
■ Disadvantages
● Hard to read/understand
ot
● Easy for errors to occur
● Hard to spot/fix errors
N
● Writing them takes up a lot of space
● Bits & bytes
○ Bits
SE
■ Binary digIT (1/0)
■ Signal on/off switch in the computer’s electronic memory
○ Byte
C
■ String of 8 bits
■ Computer organises data into a byte
IG
○ Memory
■ Area of computer that stores data as on/off signals
■ RAM (random access memory)
■ Not enough space in RAM = data stored outside RAM (slower to access)
ay
■ Processors contain registers
● Binary & denary
nj
○ Denary
■ Base 10
Sa
○ Binary to denary
■ Eg. 0101011100 to denary (348)
512 256 128 64 32 16 8 4 2 1
ia
0 1 0 1 0 1 1 1 0 0
■ Max: 16 bits
n
■ 4+8+16+64+256 =348
So
○ Denary to binary
■ Start with largest value you can subtract from the number
■ Continue to subtract until you have 0
■ Put 1 in the matching columns; 0 in all other columns
■ Eg. 40 to binary (00101000)
● 40-32=8, 8-8=0
128 64 32 16 8 4 2 1
0 0 1 0 1 0 0 0
1.2 Hexadecimal
● Digits
○ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F (Base 16)
○ Usage
, ■ Easy conversion (hex to binary vice versa)
■ Easy to read
■ Takes up less space
● Hexadecimal & Denary
○ Hex to Denary
■ Place into column
■ Multiply accordingly
■ Add them up
○ Denary to Hex
■ Divide denary number by 16
■ Result goes into the
16s column
■ Remainder goes into
es
the units
■ Larger numbers (> 225)
● Find largest column that is smaller than X
ot
● Divide X by the common value
● Divide the remainder by the next smallest value
N
● Continue until you reach the units column
● Hexadecimal & Binary
○ Convert: match with the chart
SE
C
IG
ay
nj
Sa
● Benefits
○ Can represent 16 bit words as 4 hex digits
a
○ Easy to convert digit back to binary
● Usage
ni
○ Defining colors in HTML
■ 24 bit colour
So
● Eg. #FF0000 (red), #00FF00 (green), #0000FF (blue)
○ Machine code & assembly language
■ Machine code is turned into hex
● Used to represent binary data & addresses
● Easier, faster, less errors
● Eg. 5F 3A 09 F1
■ Error messages displayed in hex code
● Eg. error #C04 door open
○ Media Access Code (MAC) addresses
■ Identifies a device on the internet
● Refers to network interface card (NIC): part of the device
● Unique address
● Static address (doesn’t change)
1. Data Representation
1.1 Binary systems
● Binary data
○ Computer
■ Electronic machine to process data
■ Data → Process → Information
○ Processor
■ Stores data using electrical switches (on/off)
■ Stores & processes data
○ Binary
■ Base 2 (on/off)
■ All data must be turned into binary for computer to process
es
■ Used for registers where a certain bit controls a specific thing
■ Disadvantages
● Hard to read/understand
ot
● Easy for errors to occur
● Hard to spot/fix errors
N
● Writing them takes up a lot of space
● Bits & bytes
○ Bits
SE
■ Binary digIT (1/0)
■ Signal on/off switch in the computer’s electronic memory
○ Byte
C
■ String of 8 bits
■ Computer organises data into a byte
IG
○ Memory
■ Area of computer that stores data as on/off signals
■ RAM (random access memory)
■ Not enough space in RAM = data stored outside RAM (slower to access)
ay
■ Processors contain registers
● Binary & denary
nj
○ Denary
■ Base 10
Sa
○ Binary to denary
■ Eg. 0101011100 to denary (348)
512 256 128 64 32 16 8 4 2 1
ia
0 1 0 1 0 1 1 1 0 0
■ Max: 16 bits
n
■ 4+8+16+64+256 =348
So
○ Denary to binary
■ Start with largest value you can subtract from the number
■ Continue to subtract until you have 0
■ Put 1 in the matching columns; 0 in all other columns
■ Eg. 40 to binary (00101000)
● 40-32=8, 8-8=0
128 64 32 16 8 4 2 1
0 0 1 0 1 0 0 0
1.2 Hexadecimal
● Digits
○ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F (Base 16)
○ Usage
, ■ Easy conversion (hex to binary vice versa)
■ Easy to read
■ Takes up less space
● Hexadecimal & Denary
○ Hex to Denary
■ Place into column
■ Multiply accordingly
■ Add them up
○ Denary to Hex
■ Divide denary number by 16
■ Result goes into the
16s column
■ Remainder goes into
es
the units
■ Larger numbers (> 225)
● Find largest column that is smaller than X
ot
● Divide X by the common value
● Divide the remainder by the next smallest value
N
● Continue until you reach the units column
● Hexadecimal & Binary
○ Convert: match with the chart
SE
C
IG
ay
nj
Sa
● Benefits
○ Can represent 16 bit words as 4 hex digits
a
○ Easy to convert digit back to binary
● Usage
ni
○ Defining colors in HTML
■ 24 bit colour
So
● Eg. #FF0000 (red), #00FF00 (green), #0000FF (blue)
○ Machine code & assembly language
■ Machine code is turned into hex
● Used to represent binary data & addresses
● Easier, faster, less errors
● Eg. 5F 3A 09 F1
■ Error messages displayed in hex code
● Eg. error #C04 door open
○ Media Access Code (MAC) addresses
■ Identifies a device on the internet
● Refers to network interface card (NIC): part of the device
● Unique address
● Static address (doesn’t change)
