Chapter 2 - Processor performance
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What are the 3 main factors which affect processor performance? 3 Marks
» Clock speed » Number of cores » Amount/type of cache memory
What is the definition of clock speed? 1 Mark
» It is the number of FDE cycles the CPU can process per second and it is measured in hertz (Hz)
Why can the CPU not perform operations faster than the clock cycle?
» Each CPU operation starts as the clock changes from 0 to 1, therefore cannot perform operations faster than the clock cycle
What is clock speed measured in ? 1 Mark
» Gighertz
What will be the consequence for a greater clock speed? 3 Marks
» More instructions will be executed » As more there is a greater rate of FDE cycles happening per second » So the program takes less time to run
What is the key feature of the Von Neumann architecture? To do with the instructions
» Instructions are fetched and executed one a time in a serial manner
What does a Dual - core processor have?
» 2 Processor linked together in the same integrated circuit
» What is the benefit of having a dual core processor?
» Each core is able to process a different instruction at the same time with its own F-D-E cycle
What is one key fact about cache?
» It is much faster than RAM
What happens when the cache fills up? 1 Mark
» Unused instructions or data still being held are replaced with more recent ones
How many types of cache level are there? 1 Mark
» L1 » L2 » L3 3
What is the fastest type of cache?
» Level 1 cache, » But it is very small, usually between 2-64 Kb
What is Level 2 cache?
» Slower than level 1, » But has a bigger size, approximately between 256Kb-2MB
What is the final cache level?
» Level 3
Why do some processors use pipelining? 2 Marks
» It is a technique used by some processors to improve performance » Reduces latency as CPU is not idle while waiting for the next instruction
What happens without pipelining? 1 Mark - To do with the FDE cycle
» The steps in the FDE cycle takes place one after the other, while one instruction is being fetched, the ALU is idle
What is the definition of pipelining? 3 Marks
» Allows the next instruction to be fetched at the same time as the previous instruction is being decoded, and the one before that is being executed » It is the concurrent processing of multiple instructions » Increases speed of execution
What are the 2 types of processor pipelining? 1 mark
» Instruction pipelinining » Arithmetic pipelining
What is the instruction pipeline? 1 Mark
» Consists of the stages which an instruction is moved through the processor » Such as it being fetched, buffered and then executed
What is the arithmetic pipelining? 1 Mark
» Represents the parts of an arithmetic operation that can be broken down and overlapped as they perform
What does each word, or group of bytes in memory have? 1 Mark
» Its own specific address
How does the processor read a word of data from memory?
» Puts the address of the desired word on the address bus
What does the wdith of the address bus determine? 1 Mark - to do with memory
» The maximum possible memory capacity of the system
What happens if the address bus consists of only 8 lines? 1 Mark - Talk about maximum address
» Maximum address it can transmit is 255 » Maximum memory capacity is 256, including the address 0