HP P Class 450/500/550/600/650/700/750 Reference Manual page 80

Interface Devices and Mass-Storage Drives
Connectors and Sockets
Socket Pin Layouts for Minitower Models
9-pin Serial Port Connectors:
Port B (left) /, Port A (right) 25-pin Parallel Port Connector
Keyboard (right) and Mouse
(left) Connectors
MIDI/Joystick Connector
USB Connectors
(two)
15-pin VGA Display Connector
3.5 mm Audio jacks
(on video adapter board)
1-Red
80 Chapter 3