SCSI: DB-25
Serial Ports: 2
Sound Output: stereo 8 bit.
ADB: 2
Ethernet: AAUI-15
Machine Gestalt ID: 52
PRAM Battery: 3.6V lithium (Maxell ER3S, Radio Shack 23-026)

Minutiae:

Apple sometimes advertises this as a 40 MHz machine, since the clock speed is doubled inside the processor chip.  However, all I/O to the processor is done at 20 MHz. 

Upgraded one SIMM at a time.

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.