PRAM Battery: 3.6V lithium (Maxell ER3S, Radio Shack 23-026)
Minutiae:
Apple sometimes advertises this as a 50 MHz machine, since the clock speed is doubled inside the processor chip. However, all I/O to the processor is done at 25 MHz.
Upgraded with one SIMM at a time.
Memory can be interleaved for approximately 10% faster RAM access. For the fastest speed, sockets 1 & 2 or 3 & 4 should contain the same capacity SIMM.
Serial Port with the phone icon supports synchronous modems, with handshaking on both output and input supported.