system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do big companies know my password when they say they’re not storing it

As the title reads. When I try to change my password to an old one on for example office, the App Store or Netflix it tells me I can’t use a previous password. How can they have that information, without storing it?
gpt
They store the hash of your password. 

Basically, if your password was "password123", they would put it through a series of standardized computations to arrive at some hash value like 456732543672. It's impossible to derive the original password from that hash, but if you're entering it again, it will again be computed into a hash and then check if the hashes match.