HP QMS 1660 - Manual (Page 183)

Storage
Options
6-45 Printer Options
3 Remove the two screws from one of the optional interface
plates on the back of the printer.
You can use either of the optional interface ports.
Save the two screws. (You’ll use them when you install the
board.) You can either save or discard the plate.
4 If you are installing an internal hard disk at this time, use the
instructions in the following section, “Installing an Internal
Hard Disk,” and then return to step 5.