Most of the ports on the back of your Apple IIGS are designed for a particular type of peripheral device (the keyboard, a joystick, disk drives, a monochrome monitor, or a color monitor), and the instructions that tell the computer how to work with that device are stored in ROM (the permanent memory of the computer). The exceptions are the two ports shown in Figure 6-2. These are general purpose serial ports, and you can change their configuration so that the computer can "talk" to a variety of different peripheral devices. You change the configuration of the serial ports by using the Control Panel Program, explained in Appendix A. If you connect a printer to the printer port, and a modem to the modem port, you probably won't have to change the configuration of the ports. Try using the device before you change the port settings.
Slots are for connecting devices that need to exchange information with the computer in a special way. The instructions that tell the computer how to communicate with that device are on the interface card you put in the slot. (The slot itself is just a plug that opens the lines of communication between the computer and the information on the card.)
Serial ports are for devices that use a serial interface for exchanging data.
Many applications will ask you to specify the location of a peripheral device by its slot number and, for a disk drive, by its drive number. If your device is connected through an interface card in a slot, you won't have any difficulty providing the slot number.
But how do you specify the slot number of a device connected to a port? You consult Table 6-1 and supply the slot equivalent for the port. Ports were designed to emulate slots so that applications could run on all models of the Apple II whether they had slots only (like the Apple IIe), ports only (like the Apple IIc), or both slots and ports (like the Apple IIGS).
Connecting peripheral devices