Addressing
If we provide a way for the switches to 'know' which 8-bit group of
switches the read/write signalling is intended for, not only could
the inputs and outputs of a single group be combined, all
of the groups of switches can be connected to the same Data Bus.
In the top picture, by applying a voltage 'pattern' to the lines marked 'A0' to 'A15', one - and only one - 8-bit group of switches will be addressed and that single group will either read-in the voltages from the Data Bus or output the contents of its latches onto the Data Bus - depending upon the 'Read/write' signalling line.
As we saw earlier, having 16 lines like this (A0 - A15), we could individually address up to 65,535 different 8-bit groups and, by using 32 lines, we could address up to 4,294,967,295.
The photograph shows part of a memory strip and the individual address and data bus lines can be seen passing from IC to IC.