Epson 486SX - Manual (Page 112)

The illustration of the main system board on page 6-3 shows
the six standard option slots inside your computer. Slot 5 is
designed for an 8-bit option card and slots 0 through 4 are
designed for 16-bit cards. As you can see below, a 16-bit card
has an extra connector along the bottom.
16-bit card 8-bit card
Usually it does not matter which slot an option card occupies,
as long as it 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 S-bit card with an additional tab along the bottom must
go into an 8-bit slot.
If you install a disk drive that uses a 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.
Installing and Removing Options 6-9