The maximum amount of total memory supported by Apple in the PowerBook 1400 is 64Mb. Individual cards may contain up to a maximum of 48Mb of DRAM.
Any combination of RAM, including the DRAM soldered to the main logic board (8Mb), the DRAM installed by Apple in the Apple factory slot (4Mb or 8Mb), and User installable RAM cards must not exceed a total of 64Mb of RAM.
Using combinations of RAM that go over the specified 64Mb limit is not supported by Apple Computer and may result in random errors.