Ok. First take an (ancient) 8 bit computer. To my understanding, and this makes sense, each ram chip has one data pin, for writing and reading, that is connected to an data bus. for the english language we have a bit over 200 common characters to represent, and so computers work with bytes at a time, because 2^8 = 256, and all our characters can be represented by a different pattern with just one byte. However, since memory chips only have one data pin, it wouldn't make sense to store an 8 bit pattern in 8 bits on the same memory chip (you would have to acess it 8 times), and so that one byte gets split across 8 ram chips (a bank) so reading a full 8 bits only takes one pass instead of 8.
A SIMM usually has 8 ram chips, so I understand the computer being able to read 8 bits at a time. But how the hec does it read 16, 32 (and now even 64) at at time? What the doodoo!?
