The title is misleading and Im not entirely sure how to word what i mean. I know what a save file is and so far from what I've learned in school, a program can read from a file and output to a file. Usually the programs that I've had to make, read in data from a .txt file and outputs to one before closing.

I made an inventory management program (no gui, all command line inputs) and so far I make an object for all the objects that the program is storing and I store them into arrays or trees but after a months worth of data, I've noticed that the structures storing the objects get huge (array size greater than 100/200). So reading from a file takes some time to do because there are a lot of objects.

How do applications and programs have their data saved? Is their data saved in a file and constantly read in from file when the program or app starts?