Have I to install SP21 on ERP8?

Hi List!
I use ERP8 (DB2UDB+W2K) w/o any SPs and updates.
Have I to install SP21? Is it necessary to install SP19 & SP20 before? Or all fixes included in SP21 already?
Could you advice me about all difficulties I will face up.
Thanks

It is not necessary to install SP19 or SP20 before installing SP21.
A SP is basically a complete system directory - you rename the old system directory and replace it entirely.
sp21_a1, sp21_b1 etc however are partial system directories - they require you have applied sp21 before applying them (however if you are applying sp21_b1 it is not necessary to have installed sp21_a1, just sp21)