J277 OCR GCSE Computer Science - Paper One: Computer Systems

Central Processing Unit (CPU)

• Purpose: Processes data instructions via the fetch-execute cycle.
• Fetch Execute Cycle:
  • Instructions fetched from RAM to CPU registers.
  • Memory Data Register (MDR) stores the instructions.
  • Control Unit decodes and executes instructions.
  • Arithmetic Logic Unit (ALU) performs calculations.
• Components:
  • Control Unit: Sends control signals, decodes instructions.
  • Registers: Temporary data storage.
  • Cache Memory: Faster access than RAM, split into three levels.
  • Program Counter: Stores next instruction address.
  • Memory Address Register (MAR): Stores current instruction address.
  • Memory Data Register (MDR): Stores fetched data.
  • Accumulator: Stores results of executions.

Von Neumann Architecture

• Key Feature: Data and program instructions stored in binary format in RAM.
• Standard Components: Control Unit, ALU, Registers, Cache Memory.
• Instruction Split: Op code (action) and Operand (data/location).

CPU Performance Factors

• Clock Speed: Measured in GHz, affects how many cycles per second.
• Cache Memory Size: Larger cache improves performance.
• Multiple Cores: More cores can enhance performance.

Embedded Systems

• Definition: Built into larger devices for specific tasks.
• Examples: Washing machines, cars, with firmware in ROM.

Storage

• Primary Storage: RAM (volatile) and ROM (non-volatile).
• Virtual Memory: Extension of RAM using HDD or SSD.
• Secondary Storage Types: Magnetic, Optical, Solid State.
  • Characteristics: Portability, Capacity, Price, Access Speed, Reliability, Durability.

Data Representation

• Binary, Denary, Hexadecimal: Different number systems.
• Binary Addition and Shifts:
  • Left shifts multiply, right shifts divide.
  • Overflow errors occur when exceeding bit capacity.
• Character Sets: ASCII and Unicode representations.
• File Size Calculation: Based on bits per character.

Images and Sound

• Bitmap Images: Pixels in a grid; Resolution and Color Depth.
• Sound Files: Sample rate and bit depth affect quality and file size.

Compression

• Lossy vs Lossless:
  • Lossy removes data permanently, reduces quality.
  • Lossless preserves original quality.

Networks

• Types: Local Area Network (LAN) and Wide Area Network (WAN).
• Network Performance Factors: Bandwidth, Latency, Interference.
• Client-Server vs Peer-to-Peer Networks:
  • Client-Server: Centralized, scalable, but dependent on server.
  • Peer-to-Peer: Decentralized, simpler, but less efficient.
• Network Hardware: Routers, Switches, NICs, Transmission Media.

Internet and Web Services

• DNS and Web Hosting:
  • DNS maps domain names to IP addresses.
  • Web hosting stores website files for access.

Network Topologies

• Star Topology: Central switch, reliable, easy to add nodes.
• Mesh Topology: Multiple paths, robust but complex and costly.

Wired vs Wireless Networks

• Wired: Faster, more secure, but less flexible.
• Wireless: Mobile, convenient, but slower and less secure.

Security

• Encryption: Scrambles data to protect during transmission.
• Malware Types: Viruses, Worms, Trojans, etc.
• Protection Measures: Firewalls, Anti-malware, User Education.

Legal and Ethical Issues

• Data Protection Act: Regulates data collection and storage.
• Computer Misuse Act: Prevents unauthorized computer access.
• Copyright and Licensing: Protects intellectual property.

Operating Systems

• Functions: User interface, memory management, multitasking.
• Utility Software: Encryption, defragmentation, compression.