Supported System Software: 7.1.2P, 7.5, 7.5.1, 7.5.3
SCSI: DB-25
Serial Ports: 2
Sound Output: stereo 8 bit.
ADB: 1
Ethernet: use Newer Technology 7ET-L10 or 7ET-C10
Machine Gestalt ID: 98

Minutiae:

Apple produced TWO DIFFERENT VERSIONS of the Performa 636CD.  The early models have one SIMM socket, but later models have two.  In the version with two SIMM sockets, one socket can take a single sided SIMM and the other a double sided SIMM.

Apple sometimes advertises this as a 66 MHz machine, since the clock speed is doubled inside the processor chip.  However, all I/O to the processor is done at 33 MHz. 

Sound output is 16-bit stereo for CD playthrough.  Sound output is 8-bit for Macintosh generated sounds.  Front headphone jack is 16-bit stereo.

Original enabler: 405

Serial Port with the phone icon supports synchronous modems, with handshaking on both output and input supported.

Has 1MB ROM and a 1.44MB SuperDrive.