A-level OCR CS 1.1.2

• Two categories of CPU core instruction sets:

  • Reduced Instruction Set Computing Systems (RISC)
  • Complex Instruction Set Computing Systems (CISC)
• Complex Instruction Set Computer (CISC):

  • Early computers programmed in assembly language
  • Developed a complex instruction set to use fewer lines of code due to slow and expensive memory
  • Example: 'MULT x * y'
  • Used in desktop/laptop computers (Intel/AMD processors)
• Reduced Instruction Set Computer (RISC):

  • Fewer instruction sets compared to CISC
  • Example: 'MULT x * y' may not exist, requiring more instructions like LOAD, PROD, and STORE
  • Smartphones and tablets use RISC (ARM architecture)
• GPU's Uses:

  • Modelling physical systems
  • Audio processing
  • Specifically designed for graphics processing
  • Important for graphics-intensive applications like games and 3D modelling
  • Also used for breaking passwords and machine learning
• Multicore Systems:

  • Processing distributed across multiple CPU cores
• Parallel Systems:

  • Computer carries out multiple computations simultaneously
  • Approaches include Single Instruction Multiple Data (SIMD) and Multiple Instructions Multiple Data (MIMD)
  • Not all operations can be processed in parallel, e.g., Fibonacci sequence
• Concurrent vs Parallel Processing:

  • Concurrent processing is an illusion of parallel processing
  • CPU can switch between processes quickly, allowing the illusion of parallel processing
  • Two tasks can't run simultaneously in a single-core CPU
  • Parallel processing is only possible in multi-core CPUs
• Reduced Instruction Set Computers (RISC):

  • Small instruction set
  • Each instruction is approximately one line of machine code and takes one clock cycle
  • Example of multiplying two numbers X and Y:
  • LDA R1, X
  • LDA R2, Y
  • MULT R1, R2
  • STO R1, X
• Complex Instruction Set Computers (CISC):

  • Large instruction set
  • Aim is to accomplish tasks in as few lines of assembly code as possible
  • Instructions are built into the hardware
  • Initially used as the standard, now more common in microcontrollers and embedded systems
  • Example of multiplying two numbers X and Y:
  • MULT A, B
• Comparison between RISC and CISC:

  • RISC:
  • Compiler has to do more work to translate high level code into machine code
  • More RAM is required to store the code
  • Pipelining is possible since each instruction takes one clock cycle
  • CISC:
  • Compiler has less work to translate high level code into machine code
  • Less RAM is required since code is shorter
  • Many specialised instructions are made, even though only a few of them are used
• Multi-core and Parallel Systems:

  • Multi-core CPUs have multiple independent cores that can complete instructions separately, resulting in higher performance
  • Parallel systems can complete tasks with a single core by using threading
  • Generally, multi-core systems perform better in larger projects than parallel systems
• Graphics Processing Unit (GPU):

  • Device with lots of independent processors working in parallel
  • Efficient at completing repetitive tasks like image processing and machine learning
  • Type of co-processor designed to supplement the activities of the primary processor