Before glass panels, specifically Primary Flight Displays (PFD) and Multi-Functional Displays (MFD), partial panel in round-gauge, six-pack panels meant losing the attitude (AI) and heading (HI) indicators as a result of losing the only vacuum pump. We dreaded when the CFII or examiner pulled out those pesky round rubber instrument covers with suction cups and announced: “you just lost the vacuum pump.”
This is a companion discussion topic for the original entry at https://www.avweb.com/flight-safety/instrument-flight/partial-panel-in-the-glass-age