Most likely, the nervous system contains one or more memory organs. We don’t know what or where they are any more so than did the Greeks, who believed it was in the diaphragm. We just know that if it exists, then it must have a great capacity.
In a computing machine, memory size can be quantified. It has a maximum capacity, which can be expressed in bits. A memory that can hold a thousand letters has a capacity of 6,450 bits, for example.
How much? How much!?!?!?! Assuming a 60 year human lifespan, a bunch of neurons, each able to receive 14 distinct digital impressions per second, and that we never truly forget things—we just focus away from them–lands us at around 35 million terabytes of data stored in the brain (aka 2.9 billion iPhones).
What is the physical embodiment of memory? One proposal is that it’s the variability of stimulation criteria—that is, the threshold of stimulation changes depending on frequency of the cell’s use. Another proposal is based on distribution of axons connecting cells—in disuse, an axon becomes ineffective over time, while in frequent use, a stimulation is facilitated by a lower threshold over a given path. Another proposal is genetic memory—chromosomes and their genes have memory elements, so perhaps this is the case in an expanded sense. There are many other suggestions also.
“Systems of nerve cells, which stimulate each other in various possible cyclical ways, also constitute memories”—this would go hand-in-hand with the “strange loops” of Gödel, Escher Bach. Likewise, vacuums-tube machines can do the same via “flip-flops”.
But we have good reason to believe that the active organs do not function also as the memory organs. That’s how early computers (the ENIAC) began, with small memory components, and with time memory components have become larger and “technologically entirely different” than active organs.