Epson Epson - Manual (Page 125)

Note
Before you install the hard disk drive, turn it over so you
can see the circuit board, as shown below. Locate the side of
the drive connector containing pin 1, indicated by a “1” or
“2” printed on the connector or the board. You need to know
the location of pin 1 when you connect the hard drive cable.
I
pin 1
Installing a Drive in the Front Internal Drive Bay
You can install a half-height, 3.5-inch drive in the front internal
drive bays.
6-4 Installing and Removing Tower Drives