Private keys are just numbers within the range of 1 and 2256. This website displays all possible private keys by splitting them into pages of 128 keys each. We do not use a database for storing all of the keys as this would be impossible due to the infinite amount of disk space needed. Instead, private keys are generated on the fly with the page number as a seed.

if you are curious where a private key is placed within the key space. Be aware that typing your private key on random websites is risky! This is a great tool for finding where already exposed keys are located.