PRAM Battery: 3.6V lithium (Maxell ER3S, Radio Shack 23-026)
Minutiae:
Apple sometimes advertises this as an 80 MHz machine, since the clock speed is doubled inside the processor chip. However, all I/O to the processor is done at 40 MHz.
Upgraded with one SIMM at a time.
It does not support 1MB, 2MB SIMMs.
The Quadra 840AV contains the 66MHz AT&T 3210 DSP chip.
Serial Port with the phone icon supports synchronous modems, with handshaking on both both output and input supported.