CMOS stores passwords. The best way to recover from a forgotten CMOS password is to disconnect the chip's power supply, thereby clearing all settings. Jumpers are used to set the motherboard's clock speed. The clock oscillator can be tuned to a specific frequency. Protected mode started with the 80286 processor and means that one application can run in a different area than another application, and they won't affect each other if one of them crashes.
All current processors can use Enhanced mode.
The 32-bit 386 was the first chip that could run both Real mode and Protected mode, without resetting the system. Parity checking requires an additional circuit and login in order to work. When a computer heats up it can change the SIMMs and cause parity errors. The POST routine can't uncover heat-related problems since everything on the board is cool. Heat problems usually cause software problems and are uncovered using software utilities.