Components of a computer

• Components inside the CPU are the:

  • Control unit
  • Busses
  • Memory address register
  • Current instruction register
  • Memory data register
  • Arithmetic logic unit
  • Accumulator
  • General purpose registers
  • Program Counter
• The control unit controls and coordinates the activities of the CPU and other components of the computer.
• The three types of bus are:

  • Control bus
  • Address bus
  • Data bus
• The memory address register holds the current location being accessed by the CPU.
• The current instruction register contains the instructions currently being executed by the CPU.
• The memory data register is used to store data that has been read from or written to main memory.
• The arithmetic logic unit performs calculations such as addition, subtraction, multiplication, division, bitwise operations, and logical operations on binary numbers.
• The accumulator is a temporary storage area where results of computations can be stored until they are needed elsewhere.
• General purpose registers are used to hold frequently accessed data during program execution.
• The ALU can also perform logical operations such as AND, OR, NOT and XOR.
• The program counter keeps track of where the next instruction will be fetched from.
• The control unit manages the fetching, decoding, and executing of instructions by the processor.
• The purpose of the control bus is to transmit command, timing and specific status information between components.
• The data bus provides a bi-directional path for moving data and instructions between components
• The address bus transmits the address of the memory location to be accessed.
• Fetch phase:

  1. The address of the next instruction is copied from the program counter to the memory address register
  2. The instruction is then copied into the memory data register. The content of the program counter is also incremented
  3. The contents of the memory data register are copied into the current instruction register
• An instruction is split into opcode and operand
• The opcode tells the CPU the type of instruction to be carried out
• The operand holds either:

  • The address of the data to be used
  • The actual data to be operated on
• Factors affecting CPU performance:

  • Number of cores
  • Clock speed
  • Cache memory size
• Clock speed is how many clock cycles the CPU does in a second
• The number of cores is how many individual processors the CPU has
• The larger the cache size the slower it is
• The cache is immediate memory located on the CPU
• Pipelining allows the processing core in the CPU to perform multiple instructions at the same time
• In pipelining, the first instruction will be fetched. When the CPU starts to decode the instruction it will also fetch the second instruction at the same time.

  When the first instruction starts to be executed, the second will be decoded and a third instruction will be fetched
• State what is meant by the term register:

  • A general-purpose storage located on the CPU
• The two main types of computer architecture are:

  • Von Neuman
  • Harvard
• Von Neuman architecture

  • Shared memory unit for data and instructions
  • A single control unit follows a linear fetch-decode-execute cycle
  • Processes one instruction at a time
  • Registers are used as fast access to instructions and data
  • Instructions and data are stored in the same format
• Harvard:

  • Instructions and data are stored in separate memory units
  • Each has its own bus
  • Reading and writing data can be done at the same time as fetching an instruction
  • Used by RISC processors
• Another more modern architecture is known as contemporary architecture
• SIMD (single instruction, multiple data)– Parallel processing is where a processor carries out a single instruction on multiple data items at the same time
• MIMD (Multiple instructions, multiple data) - Another version where multiple instructions are carried out on multiple data items across several cores
• Distributed computing – Where multiple computers on a shared network each take on a part of a bigger problem
• CISC advantages:

  • Large number of complex instructions
  • Complier can do less work
  • Small code sizes and higher cycles per second
  • Makes more efficient use of RAM
  • Multiple addressing modes available
• CISC disadvantages:

  • Has more complex hardware
  • Multiple clock cycles per instruction
  • Physically larger
  • Greater energy consumption
  • Can’t make use of pipelining
• RISC advantages:

  • Has simpler hardware
  • Smaller number of simple instructions
  • Single cycle per instruction
  • Physically smaller in size
  • Lower energy requirements
  • Can use pipelining
• RISC disadvantages:

  • Compiler must do more work
  • Large code size and less cycles per second
  • Heavy use of RAM
  • Fewer addressing modes available
• A co-processor is an extra processor unit used to supplement the functions of the primary processor
• The GPU is a type of co-processor