Paper 1 Revision vids

• Fetch-Decode-Execute Cycle


  1. Program counter copies address of next instruction into memory address register

  2. Control unit loads address onto address bus

  3. Control unit triggers read signal, causing main memory to place instruction onto data bus

  4. Instruction on data bus is loaded into memory data register

  5. Memory data register copies instruction into current instruction register

  6. Program counter incremented by 1 to point to next instruction
• Pipelining


  • Fetching an instruction while the prior one is being decoded and the one before is being executed
  • Example of parallel processing
  • Pipeline controller has to predict jump instructions to keep pipeline full
  • Mistakes cause pipeline to be emptied or flushed, degrading performance
• Von Neumann Architecture


  Single control unit and single ALU, works sequentially through instructions, stores instructions and data together in same memory unit
• Harvard Architecture


  Splits memory into separate parts for data and program instructions, accessed with different buses
• Modern CPU Architectures


  • Pipelining
  • Array Processing (SIMD)
  • Multi-core Processing (MIMD)
• CISC


  More instructions supported by CPU, requires more transistors and larger size, more power and heat, but easier software
• RISC


  Fewer instructions, less transistors and smaller size, less power and heat, but more complicated software
• Scheduling Algorithms


  • Round Robin
  • First Come First Served
  • Shortest Job First
  • Shortest Remaining Time
  • Multi-Level Feedback Queues
• Interpreter


  Converts high-level source code into machine code line-by-line, good for coding and debugging
• Compiler


  Converts high-level source code into machine code all at once, produces executable file
• Compilation Process


  1. Lexical Analysis

  2. Syntax Analysis

  3. Code Generation

  4. Optimization
• Assembly Language Instructions


  • Load
  • Store
  • Add
  • Subtract
  • Input
  • Output
  • End
  • Branch of Zero
  • Branch of Zero or Positive
  • Branch Always
• Assembly Language Programs


  • Add two numbers and output result
  • Compare two numbers and output the larger
• SQL


  Structured Query Language used for databases
• Transaction Processing


  • Changes to database that move it from one consistent state to another
  • Records may be locked to prevent interference between transactions
• Foreign key


  Present in both tables, allows tables to be joined to retrieve information from both
• The foreign key might have the same name or a different name, but it would contain the same information
• Using the correct join keyword allows tables to be joined even if the foreign key has a different name
• Transaction


  A change to the database
• Database Management System (DBMS)

  • Ensures a transaction changes the database from one consistent state to another
  • Can lock records to prevent other transactions interfering
• ACID rules


  • Atomicity
  • Consistency
  • Isolation
  • Durability
• Atomicity


  The transaction must be completed fully, or not recorded at all
• Consistency


  Any change must not break the database, must be consistent with how it was before
• Isolation


  A transaction must be isolated and not interfere with another transaction
• Durability


  A transaction must remain in the database
• Layering


  Breaking down complex network communication into separate components (layers) that each focus on one aspect
• TCP/IP stack layers


  • Application
  • Transport
  • Internet
  • Network/Data link
• Application layer


  Concerned with production, communication and reception of data, governs how data moves in and out of applications
• Transport layer


  Concerned with establishment and termination of connections between network entities, responsible for providing reliable data flow
• Internet layer


  Provides links across different network types, essential features for interoperability
• Network/Data link layer


  Passes data to the physical network (e.g. copper wire, fiber optic, wireless)
• DNS


  Domain Name System that matches domain names to IP addresses
• Domain names are constructed in a hierarchy, e.g. bbc.co.uk
• LAN


  Local Area Network, small geographic area network owned and maintained by the organization that uses it
• WAN


  Wide Area Network, large geographic area network provided and maintained by a third-party telecommunications company
• Circuit switching


  Establishment of a physical connection between two communicating entities, provides an exclusive dedicated channel for the duration of the communication session
• Packet switching


  Messages are divided into data units called packets, sent across the network by the most available/efficient route
• Modern computer networks could not use circuit switching, as it would tie up channels for too long
• Converting positive decimal numbers to binary


  Repeatedly subtract powers of 2 from the number, recording 1 for subtractions that can be done and 0 for those that can't
• Converting binary numbers to decimal

  Multiply each binary digit by its corresponding power of 2, then add the results