George Miller in 1956 had published a paper, The magic no seven, plus/minus two, propounding on the limit of short-term memory.
Ever wondered why pin/area codes or phone numbers are not more than 6 to 10 numbers long. In fact, in earlier days telephone numbers were around 7 numbers long. For example, pin code for Delhi is 110001 (six numbers long).
Miller proposed that our short-term memory can remember 5-9 items at one time if items were of same nature. Which ranges to the number 7, The Magical Number Seven.
What was the experiment?
Miller had tested set of individuals by assigning different tones varying only in pitch to produce a stimulus linked to a learned response from the study subjects. This research showed that performance was perfect up to 7th stimulus but after that, it declined upon increasing the stimulus which simply meant that after 7th tone the subjects had trouble recognizing.
This suggested that humans can essentially store about 2-3 bits of information in short-term memory. [1 bytes = 8 bits]
What is short-term memory?
For a simplistic understanding, there are essentially two types of memory centers, short term, and long term. The short-term memory block is like a cache memory of the computable device, a runtime memory.
It is easily forgettable. Only a few items go to the long-term memory block. However, both these processes are independent of each other. That is a person whose short-term memory is damaged can still have long-term memories.
Then, how is it possible that some people can memorize vast data only by glancing at it?
This happens by creating a large volume of data into smaller chunks. And in some ways, people have used memory palace to memorize sequences of numbers or words.
Example, 9634037894 this is a random set of 10-digit number. To memorize it faster there can be two ways:
1. Memorize by forming smaller chunks 9634-037-894. Now you can easily remember it.
2. Play with the information, use position, placement, association and chunking into small sets. Just by looking at the number you can notice that 4 is placed at 4th and last position so no need to memorize, now notice 9 -6 -3 comes before the fourth letter which is four and multiples of 3 in reverse order, left is 037 which is after 4th number and 89 just before the last letter.
Now you can remember it with less mental effort. Even a random 10-digit number.