Self-tapping screws are different to traditional screws as they tap their own threads when screwed into either plastic, wood or metal.
The Slotted or Minus type drive can be said to be outdated but is still quite popular in India as many small and traditional trades are using this. Another reason for the continued popularity is that many assemblies are still being done manually and workmen have the traditional screw drivers with them.
The Slotted Countersunk [CSK] self tapping screws are used to provide a flush finish to the assembly. Manufactured as per DIN 7972, these are available in Mild Steel and Stainless Steel grades 304 and 316