pagespeed insights - Why there is huge difference between PSI score of mobile and desktop sites?

Question

I want to know why there is a big difference between PSI scores of mobile site and desktop site

Answer 1

Google Page Speed Insights uses different parameters for desktop vs mobile testing.

For desktop the connection speed used is not throttled, it will load as fast as a web browser will allow (i.e. limited by round trip times, maximum simultaneous downloads per domain and CPU processing power of a decent PC).

For mobile however Google tries to simulate a real world example of a mobile phone on a 4G connection.

4 x CPU slowdown as mobile phones are less powerful and network throttling that includes slow upload and downloads and more importantly simulates a high Round Trip Time for each resource request (higher latency).