Chapter 2 - Processor Performance (1.1) Flashcards
State the factors affecting processor performance. (3)
- Clock speed
- Number of cores
- Amount and type of cache memory
How does clock speed affect processor performance?
clock speed is the time it takes for one clock cycle to complete so faster clock speed means more clock cycles can be completed
What is clock speed measured in?
gigahertz (one clock cycle per second = 1 hertz, 1 billion clock cycles per second = 1 gigahertz)
How does number of cores affect processor performance?
cores process different instructions at the same time with its own FDE Cycle, more cores means more instructions executed which means faster performance. This isn’t always the case though as software may not take advantage of all processors
What is cache?
Small, expensive, and fast memory inside CPU that stores instructions fetched from main memory in case its needed again, which is faster than going back to main memory.
How does cache affect processor performance?
More cache means more instructions stored so faster to get said instructions from cache instead of going to main memory, which means faster performance
What happens when cache fills up?
unused instructions/data are replaced with more recent ones
What is Level 1 Cache?
Extremely fast cache but small (between 2-64KB)
What is Level 2 Cache?
Fairly fast cache and medium sized (between 256KB-2MB)
What is Level 3 Cache?
Slow cache but big (often 32MB+)
What is pipelining?
when instructions are fetched while the processor is decoding or executing another instruction
Why is pipelining good?
increases processor performance and reduces CPU idle time
What is an instruction pipeline?
separates the instruction into fetching, decoding and executing
What is an arithmetic pipeline?
breaking down arithmetic operations and overlapping them as they’re performed
What happens if branching occurs during the FDE cycle?
The instruction that was fetched and decoded now has to be removed, known as ‘flushing the pipe’
