Essential Knowledge for AP Exam

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Crowdsourcing

  • Definition: Crowdsourcing is the practice of obtaining input, ideas, services, or data by soliciting contributions from a large group of people, typically from an online community.
  • Examples: Wikipedia, reCAPTCHA, OpenStreetMap.
  • Advantages: Low cost, faster results, diverse perspectives.
  • Challenges: Quality control, potential bias, misinformation.

Key Decryption

  • Definition: Decryption is the process of converting encrypted data back into its original form, usually using a key.
  • Symmetric Encryption: The same key is used for both encryption and decryption (e.g., AES).
  • Asymmetric Encryption: Uses a key pair — a public key to encrypt and a private key to decrypt (e.g., RSA).
  • Application: Used in secure communication like HTTPS (web security).

Bandwidth

  • Definition: Bandwidth refers to the maximum amount of data that can be transmitted over a network in a given amount of time.
  • Measured in: Bits per second (bps), commonly Mbps (megabits per second).
  • Higher bandwidth means faster data transfer.

Undecidable Problems

  • Definition: An undecidable problem is a problem for which no algorithm can be created that will always lead to a correct yes/no answer.
  • Example: The Halting Problem — determining whether a program will halt or run forever on a given input.
  • Significance: Shows the limits of computation — not all problems can be solved with algorithms.

Bits and Data Representation

  • Bit: The smallest unit of data in computing (0 or 1).
  • Bytes: 1 byte = 8 bits.
  • Larger Units: KB (kilobyte), MB (megabyte), GB (gigabyte), TB (terabyte).
  • Used to Represent:
    • Numbers
    • Characters (ASCII/Unicode)
    • Images (pixels in binary)
    • Audio (sampled waveforms)

Data Compression

  • Definition: Data compression reduces the number of bits needed to store or transmit data.
  • When to Use:
    • Sending data over networks (saves bandwidth).
    • Storing large files (saves space).
  • Types:
    • Lossless Compression: No data lost (e.g., ZIP, PNG).
    • Lossy Compression: Some data lost, smaller size (e.g., MP3, JPEG).