system
Given the following post, respond as if you're commenting on Reddit:
human
What actually is happening when programs load?

When a program loads, what changes to allow the user to use it? Also, how can some programs detect and display how loaded they are, when it isn't fully loaded?
gpt
Programs need to allocate resources, like RAM or network access, and have their files read. After the initial load of the executable into RAM, the program will start to load thing it must have to run. The most time consuming programs have lots of big resources like pictures, videos, and audio. Some programs get some of those things from a network which can be slower than from a hard drive. Then, when they reach a state of ready-enough, they start displaying things and loading user data. This goes on until the program is ready for the user interaction, which might cause more or different resources to load.

Programs that know and show how much stuff is coming are grabbing display cycles before all of the resources are loaded. They know what is needed, so they can give you that progress or countdown.