What is the difference between sliding window systems: HST, PSK and SMART-SLIDE?

The main differences between PSK, HST and SMART-SLIDE are:

• Opening method:
  • HST: the window rises a few millimeters and moves
  • PSK: the window opens and moves, hiding behind the fixed sash
  • SMART-SLIDE: the window opens and moves, hiding it behind the fixed sash
• Threshold height:
  • HST: thresholdless
  • PSK: has a threshold (the height depends on the profile)
  • SMART-SLIDE: has a threshold
• Size:
  • HST: large
  • PSK: average
  • SMART-SLIDE: medium