A high pressure BLISK includes at least one circular row of airfoils circumferentially disposed about, integral with, and extending radially outwardly from an annular rim having an annular flat aft facing face with coplanar radially outer and inner face portions radially separated by an annular undercut extending into the rim from the aft facing face. Airfoil roots including root fillets extend around the airfoil between the rim and pressure and suction sides of the airfoils. An axially aftwardly extending annular cylindrical section extends aftwardly from the flat face. The BLISK being a first of axially adjacent first and second rotor sections connected by a rabbet joint. A forward arm of the second rotor section includes an outer forward facing annular face spaced apart from the aft facing face radially outwardly of the annular undercut and a radially inner forward facing annular face contacting the aft facing face.