IBM B50 - Manual (Page 104)

Summary of Boot Options and Control Keys
You can press the following keys when the keyboard POST indicator appears.
Key Result
F1 (display keyboard) Normal mode boot, graphical System Management Services starts.
1 (ASCII keyboard) Normal mode boot, text-based System Management Services starts.
F5 (display keyboard) Service mode boot, default boot list.
5 (ASCII keyboard) Service mode boot, default boot list.
F6 (display keyboard) Service mode boot, custom boot list.
6 (ASCII keyboard) Service mode boot, custom boot list.
F8 (display keyboard) Normal mode boot, Open Firmware command line.
8 (ASCII keyboard) Normal mode boot, Open Firmware command line.
5-4 7046 Model B50 Service Guide