How Fast Is My CPU?

How fast is my CPU?

Thirty years ago this question was easy to answer. Consider the i486DX2-50 - one of the first CPUs able to decode mp3 without stuttering and the one recommended for Windows 95.

This is an in-order CPU, thus instructions executed can be directly translated to microseconds gone. With a single memory cache and a known TLB the memory hierarchy is still manageable. Performance wise it could add two 32-bit registers in one cycle and thereby produce 200 MB per second. It would consume around 4W for this task.

Contemporary CPUs are much more complex: they support out-of-order execution, to many instructions, various caches, multiple cores, hyper-threads, turbo-boost and dozens of other extensions.

My laptop for instance comes with a Zen3+ CPU. Each of the eight cores can add two 256-bit registers with a single instruction. Four of these instructions can be issued per cycle. This means each cycle 1024 bytes may be produced.

The frequency of the CPU can be between 1.6 and 4.7 Ghz. In practice, it is limited by the thermal design power of 28 Watt. For dense code running on all eight cores 3.6 Ghz can be achieved. Thus, my laptop CPU can produce up to 3.6 TB per second, albeit no memory is large and fast enough to store this data.

This represents more than four orders of magnitude improvement over 30 years. Or roughly doubling the performance every two years.