CIE AS-Level Information Technology 9626 Theory Summary

Data, Information, Knowledge, and Processing

  • Data: Raw, unorganized collection of text, numbers, symbols, images, or sound.
  • Information: Processed data with context and meaning.
  • Knowledge: Acquisition of facts or information required to solve problems.
  • Sources of Data:
    • Static: Remains constant (e.g., CD-ROM).
    • Dynamic: Changes automatically (e.g., live stock prices).
    • Direct: Collected first-hand; relevant and up-to-date but time-consuming.
    • Indirect: Secondary source; available immediately but potentially biased or outdated.
  • Quality of Information: Defined by accuracy, relevance, age, level of detail, and completeness.
  • Encoding Formulas:
    • bitrate=samplerate×bitdepth×number of channelsbit rate = sample rate \times bit depth \times \text{number of channels}
    • Measured in kilobits per second (kbpskbps).
  • Compression types:
    • Lossy: Reduces file size by removing data/quality (e.g., JPEG, MP4).
    • Lossless: Reduces size without quality loss (e.g., PNG, DV).
  • Encryption:
    • Symmetric: Same key for sender and receiver.
    • Asymmetric: Uses a Public Key for encryption and a Private Key for decryption.
    • Protocols: SSL/TLS for HTTPS; provides security for web and email.
  • Data Accuracy Checks:
    • Validation: Matching data to rules (Presence, Limit, Range, Type, Length, Format, Lookup, Consistency).
    • Verification: Checking data matches the source (Visual checking, Double data entry).

Hardware and Software

  • CPU Components: ALU (Arithmetic Logical Unit) for calculations; CU (Control Unit) for the fetch-execute cycle.
  • Storage Media:
    • HDD: Magnetic, non-volatile, moving parts, cheaper per MB.
    • SSD: Flash memory, no moving parts, 20% faster than HDD.
  • Printers:
    • Laser: Uses toner; fast (50−200 ppm50-200\,ppm); high quality.
    • Inkjet: Uses CMYK ink; cheaper initial cost; used for photos.
    • Dot Matrix: Impact printer; slow; used for continuous multi-part forms (e.g., receipts).
    • Plotter: Creates vector drawings on large paper (A2,A1,A0A2, A1, A0).
  • Software Types:
    • System Software: Operates/maintains hardware (OS, Device Drivers, Utilities).
    • Application Software: Productivity tasks (Word processors, DBMS, Graphics software).
  • User Interfaces (UI):
    • CLI: Text commands; low memory usage; hard to learn.
    • GUI: WIMP (Windows, Icons, Menus, Pointers); intuitive.
  • Translators:
    • Compiler: Translates whole HLL program into machine code at once.
    • Interpreter: Translates HLL code line by line during execution.

Monitoring and Control

  • Sensors: Input devices for physical environments.
    • Pressure: Uses Piezoresistance.
    • Moisture: Uses Capacitive measurement.
    • Light: Uses Photoresistors.
  • Actuator: A motor that controls a mechanism or system.

E-safety, Health, and Safety

  • Threats:
    • Phishing/Vishing/Smishing: Gathering data via email/voice/SMS.
    • Pharming: Malicious code redirecting to fake websites.
    • Malware: Trojan Horse, Worms (replicate across networks), Spyware, Rootkit, Ransomware.
  • Health Issues:
    • RSI/Carpal Tunnel: Hand/arm pain from repetitive movement.
    • DVT: Blood clots from sitting too long.
    • Eye Strain: Caused by long periods of screen use.

Network Systems

  • LAN: Small area, high speed (1 Gbps1\,Gbps), high security.
  • WAN: Large area, lower speed (200 Mbps200\,Mbps), uses third-party infrastructure.
  • Client-Server: Centralized control, secure, requires technical staff.
  • Peer-to-Peer: Decentralized, cheaper, slower as more computers join.
  • Internet Infrastructure: Regulated by ICANN (names), IEFT (standards), and W3C (web standards).
  • Mobile Networks:
    • 1G: Analogue.
    • 2G: Digital signal.
    • 3G: Up to 2 mbps2\,mbps.
    • 4G: Theoretical speeds up to 1 Gbps1\,Gbps.

Expert Systems and Processing

  • Expert System Components: Knowledge base (database of facts), Inference engine (reasoning rules), User interface.
  • Processing Models:
    • Batch: Data processed at set intervals in groups.
    • Online: Processed in small transactions.
    • Real-time: Processed immediately (vital for safety/immediacy).

Spreadsheets and Databases

  • Test Data Types: Valid, Invalid, Extreme valid (boundary), Extreme invalid.
  • Modeling/Simulation: Predicts real-world behavior; reduces prototype costs and risks.
  • Database Structure: Tables (entities), Records, Fields (attributes).
  • Normalization:
    • 1NF: Atomic fields, no repeats.
    • 2NF: Meets 1NF, related fields separated into tables.
    • 3NF: Meets 2NF, no transitive dependencies (fields not directly related to primary key removed).

Sound and Video Editing

  • Frame: Single still image in a video; standard is 24 fps24\,fps, HD is 50−60 fps50-60\,fps.
  • HD Resolution: 1920×10801920 \times 1080 pixels.
  • Rendering: Combining effects to create the final output file.
  • Aspect Ratio: Ratio of width to height.