Supported System Software: 7.1, 7.1.1(Pro), 7.5, 7.5.1, 7.5.3
SCSI: DB-25
Serial Ports: 2
Sound Output: stereo 8 bit.
ADB: 2
Ethernet: optional  AAUI-15 or upgrade to Newer Technology 7ET-N10/100 using a NuBus adapter
Machine Gestalt ID: 52

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.

Can be accelerated with Newer Technology's "MacClip™", part # 7MC040-SC.  The world's smallest Macintosh accelerator.

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.