1.1 - Systems Architecture
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What is the purpose of the CPU?
To fetch, decode and execute instructions from memory
What are the components of the CPU?
• Arithmetic Logic Unit (ALU) • Control Unit (CU) • Cache • Registers
What does the Arithmetic Logic Unit (ALU) do?
Carries out maths and logic calculations
What does the Control Unit (CU) do?
Coordinates the FDE cycle and decodes instructions
What is cache?
Small, fast memory that holds frequently accessed items
What are the 4 registers?
• Memory Address Register (MAR) • Memory Data Register (MDR) • Program Counter • Accumulator
What does the Memory Address Register (MAR) hold?
Address of the instruction that is to be fetched
What does the Memory Data Register (MDR) hold?
Holds the data value being fetched or stored.
What does the Program Counter hold?
Address of the next instruction to be fetched from memory
What does the Accumulator hold?
Results from Arithmetic Logic Unit (ALU) calculations
What happens in the fetch stage of the FDE cycle?
• Instruction is fetched from memory using the address in the Program Counter • Program Counter changes to the next instruction’s address
What happens in the decode stage of the FDE cycle?
Instruction is interpreted by the Control Unit
What happens in the execute stage of the FDE cycle?
• Instruction is carried out • Any additional data is fetched • Results may be written to memory
What are factors affecting the speed of the CPU?
• Clock Speed • Number of Cores • Cache Size
What is Clock Speed?
The rate at which the FDE cycle is carried out per second (GHz)
What does having more cores do?
If software allows it, each core can execute an instruction at the same time, increasing the speed of the CPU
What does having a larger cache size do?
More regularly used items can be held, reducing reliance on the slower RAM, increasing the speed of the CPU
What are embedded systems?
A specialised computer system built into a larger machine designed to perform a few functions