Epson EISA Desktop - Manual (Page 94)

If you install two hard disk drives, you must change the jumper
settings on each drive to indicate which is the master (primary)
and which is the slave (secondary). The primary drive is the
one from which you boot your computer.
Changing the Jumper Settings
The following illustration shows the location of the jumpers on
the optional Epson 200MB IDE hard disk drive.
If you are installing another type of Epson hard disk drive, the
jumpers may be in a different location, and there may be four
jumper positions instead of two. The 200MB drive has only two
jumper positions: C/D and DSP. Your drive may have four
positions: HSP, C/D, DSP, and ACT.
6-4 Installing and Removing Drives