It is possible to use the launcher to run versions of Minecraft from nearly any era.
However, not every version of the game is included (to see a list of all missing versions, see versions not in the launcher).
This will destroy your saved data ( although you can back that up).
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The current launcher is the sixth launcher for Minecraft, and the second that was built to automatically update itself.
Every time the launcher is executed, it checks a specific directory where Minecraft stores its files called ".minecraft".
It checks a file called "launcher_profiles.json" for login credentials.
The launcher also controls most of the technical stuff that goes on with the game; it is responsible for downloading java packages, it consists of all the game’s resources for example its textures and it’s also the window through which you’ll be updating your game whenever one becomes available so it’s pretty clear that it’s really important.
It is responsible for downloading the main Java packages, including minecraft.jar, which holds the code and resources of the game such as textures, and LWJGL.
It also acts somewhat like a basic and easily bypassable copy-restriction by forcing the user to login to a paid account when running for the first time.
All things considered, the Minecraft Launcher is a pretty key aspect of this game and does an excellent job of providing users the utmost amount of convenience.
The Minecraft launcher is the login and downloader front-end to the stand-alone client.