I've come across people of different age brackets who claimed they have issues committing information to memory. With no signs of either retrograde or anterograde amnesia, people tend to find it quite difficult to retrieve information from memory stores in the brain.
There are structures in the brain which subserve memory functions: the prefrontal cortex, hippocampus, cingulate gyrus and other parts of the limbic system.
The way the brain effectively stores information such that encoding and retrieval of such information is made easier is by assessing the relationship between the new information and an already facilitated and habituated existing memory. The limbic system plays a very important role in this processing of memory.
For example, to understand a musical piece, the brain doesn't try to memorize each note of the piece, but does try to assess the relationship between each note.
In essence, one active way of effectively memorizing information is by relating that information with an already existing and well facilitated memory,without having to verbally repeat such information over and over in order to commit it to memory.
Even when dealing with digits, you either find the relationship between the digits or relate them closely with previously existing digits stored in memory stores of the brain.
This is how I have come to know all details on 3 of my debit cards, and a lot of other pieces of information.
Finally, actively committing information to memory effectively helps reduce the amount of energy needed for retrieval of memory.