Communication Slot

The Apple Communication Slot, or Comm Slot,[1] is an internal expansion data interface (slot) found in Apple Macintosh computers from the early to mid-1990s.[2] It was designed as an inexpensive way to add communication expansion cards like network adapters or modems to Macs and Power Macs.[3]

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.[4] 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.[1] Computers that came with this card installed had the modem port blanked out (though the connector was still present).[citation needed] 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.

Compatible computers

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.

Communication Slot II

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.


Communication Slot

Communication Slot II

Additional cards were offered by third parties.


  1. ^ a b O'Grady, Jason D. (2009). Apple Inc. ABC-CLIO. p. 86. ISBN 0313362440. Archived from the original on March 27, 2022. Retrieved September 27, 2022 – via Google Books.
  2. ^ Quinlan, Tom (April 25, 1994). "Apple enhances Performas, promises PowerPC upgradability". InfoWorld. IDG Communications. 16 (17): 25. Archived from the original on March 3, 2022. Retrieved September 27, 2022 – via Google Books.
  3. ^ Cronk, Drew J. (February 1995). "Expansion Slots". MacUser. ZDNet. 11 (2): 92–93 – via the Internet Archive.
  4. ^ Lerner, David; Aaron Freimark (2002). Macintosh Troubleshooting Pocket Guide for Mac OS. O'Reilly Media. p. 49. Archived from the original on November 11, 2021. Retrieved September 27, 2022 – via Google Books.
  5. ^ a b c Yune, Tommy (March 30, 2018). "Low End Mac's Guide to Comm Slots". Low End Mac. Archived from the original on September 27, 2022. Retrieved November 10, 2021.