Processor Performance Flashcards
What are cores?
Processors
Does doubling the amount of cores double the speed of the computer system?
No, but more cores will achieve a significant improvement because data and instructions need to be fed to the cores appropriately and so the computer system will need to spend time organising which cores receive which data and instructions. Also, the efficiency of a multicore processor depends on the nature of the required task, i.e. if it is possible to divide a computation into subtasks that can be processed in parallel (one task per core at the same time). This is known as parallel processing and it is only possible on multicore systems.
What is a cache?
A cache is a fast, relatively small capacity set of locations that sit close to the processor; it is used to store the instructions and data most frequently used.
What is L1 Cache?
Smallest and fastest cache, part of the circuitry of each core A quad-core CPU would have four L1 caches
What is L2 Cache?
Cache shared by cores. It is slower than L1 cache and tends to be larger. In new systems, the L2 cache is usually part of the core in the same way as the L1 cache.
What is L3 Cache?
L3 cache is slower than L2 cache but larger. It sits on the processor or near it on the motherboard.
What is L4 Cache?
Newer systems incorporate an L4 cache. As with L3, this is placed on or near the processor.
How does cache size affect system performance?
The larger the cache, the more instructions can be queued and carried out. Storing instructions in cache reduces the amount of time it takes to access that instruction and pass it to a CPU core. If a system does not use caching, then there is an increased need for accessing the main memory, thereby increasing the time it takes for an operation to be carried out.
How does cache speed affect system performance?
The faster the cache, the faster an instruction is fetched to the processor. Where cache is placed is also important. Having L2 cache as part of the circuitry of each core reduces the time it takes for instructions and data to pass through the system registers. This increases the speed of processing and thereby allows instructions to be carried out more efficiently. The greater the number of cache levels, the more efficient the system
How does clock speed affect system performance?
The greater the clock speed, the faster instructions are carried out. Clock speed is usually measured in GHz (gigahertz)
What is word size?
The amount of data that can be handled at one time by the processor
How does word size affect processor performance?
The larger the word size, the greater the amount of data that can be transferred to the CPU in one pass. Being able to pass larger amounts of data to the processor with every pass, the system is likely to carry out instructions faster.
What is pipelining?
Pipelining is a technique for breaking down a sequential process into various sub-operations and executing each sub-operation in its own dedicated segment that runs in parallel with all other segments.
I.e. when one instruction is being executed, the next is being decoded and the one after being fetched.
