AP Computer Science P Unit 2 Cheatsheet: Data

• Bit: Binary digit; either 0 or 1
• Byte: 8 bits
• Digital representation: All data stored as combinations of bits
• Abstraction: Bits grouped to represent numbers, characters, colors, etc.
• Key insight: Same bit sequence can represent different data types depending on context (e.g., 01000001 = 65 in decimal OR 'A' in ASCII)

Fixed-bit integers: Limited range causes overflow when result exceeds maximum representable value.

Real numbers: Fixed bits cause roundoff errors—some real numbers stored as approximations only.

Language differences:

• Some languages (like those on AP exam) use abstraction to represent integers limited only by memory
• Others use fixed bits, creating strict limits

Test focus: Understand that bit limitations create errors; don't memorize specific ranges.

Key principles:

• Compression depends on redundancy in original data AND algorithm used
• Fewer bits ≠ less information (context matters)
• Lossy compression often produces smaller files than lossless compression, but not always.