Epson EL 3S/33 - Manual (Page 67)

4. Align the hard disk drive so that the cable connectors are
facing the diskette drive bays and the four holes at the base
of the drive are above the four pegs, as shown below.
pegs
5. Gently lower the drive over the pegs. When the hard disk
drive is resting on the pegs, it will not move from side to
side.
6. Lower the mounting bracket over the hard disk drive,
making sure that the tabs on the computer align with the
slots in the mounting bracket.
4-8 Installing and Removing Drives