The Apollo guidance computer had 36 K words of core rope ROM. To address 36864 words, a 15 bit memory address for up to 32768 words is not enough, 16 bits are needed.
This Wikipedia article describes the ROM addressing. The 10 lower bits of the address field of an instruction select the word within a 1024 words.
There is an Fbank register of 4 bit to select the ROM bank and 1 bit Sbank extension to address the last 4 kilowords.
But a bit is missing, 10+4+1 is 15 only and we need 16 bits. Therefore the Fbank register should be 5 bits, not 4.
Am I right about the size of the Fbank register?