Epson 486SX User 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
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:
go into an 8-bit slot.
the card as close as possible to the drive it is controlling.
Consult the instructions that come with the card to see if
this is the case.
8-bit card
Installing and Removing Options
6-9