Apple Performa 6400/180 - Manual (Page 31)

Basics Expansion Bay - 29
Expansion Bay
The expansion bay includes audio, data, and power
connectors for adding a SCSI CD-ROM or other SCSI device.
The bay is configured for 5.25-inch devices, but with
modification to the carrier, a 3.5-inch SCSI device could be
installed. In some computers, the bay may already be
occupied by a Zip drive.