Guidance on choosing CPUs

This is a short guide covering some issues concerning modern CPU performance and how to hopefully choose the best CPU for your task.

Clock speed and Single threaded performance

Historically processor performance (at least within the Ix86 architecture) could be aligned with clockspeed which improved steadily year on year, the '80s and '90s saw cpu performance double every 18-20 months. until the mid 2000s when it seems that chip design hit a number of limits (heat dissipation, die size...) which effectively stalled CPU speeds at around 3-4GHz(1). Since then CPU development has largely concentrated on hypertrheading and multicore designs and to a certain extent the server architecture has followed (NUMA).

Core density

Can I rely on clock speed as an indication of processor speed and thread performance?

Broadly speaking no. All other things being equal a 2.0 GHz core will be faster than a 1.8 GHz core however those other factors include cache size, processor architecture, bus architecture, bus speed, phase of the moon... Other than within a particular processor range it's very dangerous to look at clockspeed and assume that a faster clockspeed with mean better performance. This is especially so with Single threaded apps.

References

Multi-core and multi-threading performance (the multi-core myth?)

-- IainRae - 03 Aug 2014

• graphs showing specfloat figures for various CPUs against their release date:
  

Notes

(1) Whist improvements in processor clockspeed have been made through architecture design (bulldozer etc) these architectures also have limits.