02. Data representation and character encoding - revision mindmap
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Bits and place value
- Bit, nibble, byte; 1 nibble = 4 bits
- Bases 2, 10 and 16; digits allowed in each
- Digit contribution = digit × base to position
- Unsigned n-bit range: 0 through 2ⁿ−1
Conversion routes
- Binary/hex to denary: sum weighted digits
- Denary to binary/hex: repeated division and reverse remainders
- Binary ↔ hex: one four-bit group per hex digit
- Fixed width: preserve leading zeroes and label the base
Conversion algorithms
- Input contract: integer quantity or digit string
- Iterative state: quotient, remainder, output
- Recursive state: smaller quotient and returned text
- Hex-string mapping: digit → nibble → concatenation
Computing applications
- Decimal: human-facing quantities
- Binary: digital data and instructions
- Hex: compact addresses and RGB notation
- Same value, different representation; storage versus display
Characters and encoding
- ASCII: 7-bit codes, 128 characters
- Unicode: code points across scripts and symbols
- UTF-8: variable-length byte encoding
- ord and chr: code point ↔ Python character
Worked example & exam traps
- 45 in base 10 = 0010 1101 in base 2 = 2D in base 16.
- 2 × 16 + 13 = 45; 0A in hex = 0000 1010 in binary.
- ord(‘A’) = 65; chr(65) = ‘A’. Code point is not a byte sequence.
- Avoid: code point = encoded bytes; Unicode always 16 bits
Sources and reading
This map condenses Chapter 02 and its source trail. Use the self-learning reading guide for the corresponding VJC pages and A notes. It does not add topics to the stated promo scope.