You have maybe see that, HTC install different processors on HTC One S. If you have bought it few weeks ago it must be a S4 but if you have bought it few days ago it could be a S3.
Just be careful about that because S4 roms can't run on S3 and S3 roms can't run on S4!
You can maybe try to know if you have a S3 or S4 with 2 different apps:
CPU Spy & Quick System info:
But How To know that?
If your processor run 1512 MHz it must be a S4 if it runs 1700MHz it must be a S3!
I can't be held responsible!!!
Links Pictures & Video:
Play Store: https://play.google.com/store/apps/details?id=com.bvalosek.cpuspy
Quick System info:
Play Store: https://play.google.com/store/apps/details?id=org.uguess.android.sysinfo
This is a S4