Slot 5 is designed for an 8-bit option card, and slots 1 through 4 are designed for 16-bit cards. As you can see below, a 16-bit card has a second connector along the bottom.

8-bit option card

16-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 connector along the bottom must go in the 8-bit slot.

If you install an additional disk drive that uses a controller card, place the card as close as possible to the disk 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 Options 5-9