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CPU performance and cache
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Why is one computer faster than another? Three CPU features make most of the difference.
Clock speed
The clock speed is how many cycles the CPU runs per second, measured in hertz. 3 GHz = 3 billion cycles per second.
A higher clock speed means more instructions can be processed each second.
A higher clock speed means more instructions can be processed each second.
Cores
A core is a complete processing unit. A quad-core CPU has 4 cores that can each work on instructions at the same time.
More cores help when tasks can be split up, but doubling the cores does not always double the speed, because some tasks cannot be split and cores must coordinate.
More cores help when tasks can be split up, but doubling the cores does not always double the speed, because some tasks cannot be split and cores must coordinate.
Cache
Cache is a small amount of very fast memory inside or very close to the CPU. It holds frequently used instructions and data, so the CPU waits less for slower RAM.
A larger cache holds more, so the CPU finds what it needs more often.
Types (levels): L1 is the smallest and fastest; L2 is larger and a little slower; L3 is larger again and often shared between cores.
A larger cache holds more, so the CPU finds what it needs more often.
Types (levels): L1 is the smallest and fastest; L2 is larger and a little slower; L3 is larger again and often shared between cores.
A CPU has the same clock speed and cores as another, but a bigger cache. Explain why it may be faster.
- More instructions and data can be held in cache.
- The CPU needs to fetch from slower RAM less often.
Answer: It finds more data in fast cache, so it waits less for RAM.
CPU performance depends on clock speed (cycles per second), number of cores (parallel work) and cache size and type (fast memory near the CPU; L1 fastest, L3 largest).
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