The Apple Communication Slot or Comm Slot is an internal expansion data interface (slot) found in Apple Macintosh computers from the early to mid-1990s. It was designed as an inexpensive way to add communication expansion cards like network adapters or modems to Macs and Power Macs.
The slot exists in two forms. The original Communication Slot standard was introduced in the Macintosh LC 575 and can be identified by the notch toward its rear. This slot is based on the LC PDS. An updated PCI-based Communication Slot II debuted with the Performa 6360. This new slot moved the notch to the front so that incompatible cards could not be inserted.
In addition to the respective expansion bus pins, these slots also carried audio and serial lines. The serial bus was shared with the external modem port. Because the power and serial pins remained unchanged between the two slots, it was possible to design a universal modem card which could work in either. Network adapters, however, needed to be designed for one or the other.
A major disadvantage to both is that when a modem card is installed in the Communication Slot, the modem serial port on the back of the computer is disabled. Computers that came with this card installed had the modem port blanked out (though the connector was still present). Further, due to its unconventional architecture, the Performa 5200's printer port would be disabled if a network adapter was installed in the Communication Slot.
A Communication Slot (some documentation refers to this as a Communication Card I Slot) is found in some 68040 and PowerPC CPU Macs.
The Communication Slot II was used in the 6360 and later series of Power Macs and Performas.
In addition, a modified Communication Slot II was present on the Power Macintosh G3 personality cards. This slot only provided power and serial lines, leaving the PCI pins disconnected. For this reason it could only be used with modem cards. As in other machines, the external modem port is disabled when a modem is installed in the Communication Slot.
Additional cards were offered by third parties.