Epson Equity 320SX PLUS - Manual (Page 112)

Slots 1 through 3 are designed for 16-bit option cards and
slot 4 is designed for an 8-bit card. As you can see below, a
16-bit card has an extra connector along the bottom.
16-bit option card B-bit option card
Usually it does not matter which slot an option card occupies
as long as the card fits in the slot. For example, you can place
some 8-bit cards in a 16-bit slot. However, you must follow
these guidelines when deciding which slot to use:
An 8-bit card with an additional tab along the bottom
must go into an 8-bit slot.
If you install a disk drive controller card, place the card as
close as possible to the drive it is controlling.
Some option cards must be installed in a specific slot.
Consult the instructions that come with the card to see if
this is the case.
6-10 Installing and Removing Options