Scientists found storage capacity of synapses by measuring their size. They found, on average, a synapse can hold about 4.7 bits of information. This means that the entire human brain has a capacity of one petabyte. This is same as about 20 million four-drawer filing cabinets filled with text.
Striving around this stuff, I have a weird doubt crawling in my mind and it goes like this: Why is it like this that a human whose brain has got a capacity to store 1 petabyte, i.e. 1 million GB, cannot fully remember even the contents and information of a simple textbook which on the maximum would not be more than 1 GB, when he has to appear in exam? Why is storage capacity not directly linked with remembering capacity?