When does a cpu start to get bottlenecked by an HDD?

[Rafael Mestdag]

I used to have an FX6300 and now I have an i5 3570K which is way faster according to any decent benchmark on the internet. I almost always used HDDs instead of SSD's and despide that, after I got the i5 I noticed an amazing difference in terms of both the loading times and the performance of 3d applications, especially games.

My using HDD's seems to make no difference at all, it's apparently not a bottleneck to the 3570k.
So my question is, when does a cpu start to get held back by an HDD?

 

[n0ns3ns3]

Anytime it needs data from HDD.
That's why programs loading to RAM.
in some open world games, you will notice a stutter/freezes with HDD.