I feel like this question has never really been asked before but I’ve always wondered even with The Sims 2 as well. Basically I’m just wondering what the purpose of the initial loading screen is.

I get that if you have gameplay mods it seems to process those during the loading screen, but if you don’t, what else is the game doing in the background during startup that still makes it take ~60 seconds? All it does is bring you to a main menu and then an even longer loading screen after (which I understand is for loading up the selected world/save). But that first loading screen has always intrigued me. I figured MTS would be a good place to ask a technical question like this.

It’s loading up the settings and the non-world-based gameplay

Meanwhile the worlds load up the world and sims themselves

Loading all of the game and expansion pack assets into memory, which requires reading the registry, putting a file lock on the files, reading, buffering, swapping etc.
This includes reading the userdata as well, as you noted.
When you arrive at the loading screen and choose your world or savegame, that data is read, buffered, swapped etc., so that the computer has that information in memory and can send it to the screen. This also involves using system library file assets, such as Directx, .net, device drivers and so on.
It takes time for a computer to read information from a hard drive (or SSD) and put it into use!

(I'm sure someone more knowledgeable than me can correct my inaccuracies and give a more detailed response )
Edit: I found a video too: https://www.youtube.com/watch?v=lHrK1kw7ZMw

You can get real nosey with it if you use something like Microsoft's Process Monitor (ProcMon). Then you can watch the file access in real-time when you boot the game

That’s a great idea! Thank you everyone!

I’ve begun to wonder recently as well with TS3 if the speed of the initial loading screen is bottlenecked by the animations. Take Late Night for example as it has lots of animations during load up; I’m curious if even with the best CPU on the market you’d have to wait for the animations to finish before reaching the main menu… I love the fun loading screens. Just more technical thoughts.