Internal RAM and SFRs of 8051 microcontroller

[@animationwallah]

If there is only 21 SFRs in 8051 so why they have occupied 128 bytes of memory unnesessorry if not then why ?

[@ravirajpawar9353]

It may be reserved for future use.In addition to the existing 21 SFRs , the new derivatives of 8051 microcontroller family provides new features with additional SFRs.These new SFRs occupy the certain locations from unused space of SFR(80H to FFH).Still there are unused locations left.