Supported System Software:6.0.5 through 7.0.1, 7.1, 7.1.1, 7.5, 7.5.1, 7.5.3
SCSI: DB-25
Serial Ports: 2
Sound Output: stereo 8 bit.
ADB: 2
Ethernet: use Newer Technology 7ET-N10
Machine Gestalt ID: 13

Minutiae:

Upgraded with four SIMMs at a time.

The memory used in the IIfx resembles Apple's 32-bit (72 pin) SIMMs, however they are 8-bit (64 pin) SIMMs.  The only place, outside of a IIfx, where they can be used is in LaserWriter IIntx printers.  To be used in the IIntx they must be 1MB SIMMs, and they must be used in groups of four.

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

Has 512KB ROM, and a 1.44MB SuperDrive.

This Mac contains a unique 32-bit Processor Direct Slot (PDS).