HP LaserJet Enterprise M4555 MFP series - Manual (Page 280)

Install external I/O devices
This product is equipped with an external I/O (EIO) slot. You can install an additional HP Jetdirect print
server card or external EIO hard drive in the available EIO slot.
NOTE: This example shows installing an HP Jetdirect print server card.
1. Turn the product off.
2. Disconnect all power and interface cables.
NOTE: This illustration might not show all the cables.
260 Chapter 12 Manage and maintain ENWW