The numbered jar files in your
versions/* folders work exactly like the old
bin/minecraft.jar file used to. Now there are just multiple copies of
minecraft.jar all renamed to keep them separate.
If you're using a 3rd-party launcher, you can copy the
1.5.1.jar file in your
versions/ folders to wherever your launcher keeps its version of Minecraft. Rename the copy of
minecraft.jar and proceed from there. If this is your situation, this is where my instructions end because I don't know your launcher's setup.
However, you can also use the new Minecraft launcher directly, leveraging its new multi-version features. This is what I'm doing now, since I find it more robust than messing with other launchers. Here's a step-by-step guide to get you to the point where the mod's install instructions will make sense again:
Make a copy of your
versions/1.5.1 folder and put it beside the 1.5.1 folder. Rename the new folder, the jar file, and the JSON file all to
.json extensions as appropriate (OS X may not show you the extension of the files, in which case don't worry, they'll be unchanged and stay correct). You should now have a
versions/aether2/ folder containing
(The name "aether2" is not important – it could be anything, so long as you use the exact same name in every place where
aether2 appears in these instructions. Stick with
aether2 until you grok the process.)
Then open the JSON file with a text editor (not Notepad, since it mangles config files; use Wordpad, or get Notepad++). Change the line inside that reads
aether2 (or whatever you named the files and folder)
and save the JSON file.
Now you will have a nice fresh new Minecraft jar version that you can start modding. This is why the new Minecraft launcher is awesome – it supports multiple versions, including multiple modded versions.
(Yes, you have to use the 1.5.1 version as a starting base. Aether II isn't updated to 1.6.2 yet.)
Now that you've got that, you need a new folder to keep your world saves and mods separate from the vanilla Minecraft files. Create a folder anywhere (I like to keep it in my
.minecraft folder though) named whatever you like, but for convenience I suggest (you guessed it)
aether2. This folder name doesn't have to match the names under
versions/, but it's convenient for it to match.
Finally, you need to create a new launcher profile that will use the new version and new folder. Start the Minecraft launcher and create a new profile, then click Edit Profile. Change Profile Name to something nice like "Aether II". Click the checkbox beside Game Directory and change the end of the path to point at your new world folder, so something like
(or the equivalent on the other operating systems). Now, and this is the all-important part, pick
aether2 from the Use version dropdown list. Double-check that your Minecraft login is correct (especially if you share this computer with other Minecraft players), then click Save Profile.
You should now have a nice new login profile that runs a copy of Minecraft that's entirely separate from the vanilla Minecraft release!
You are now ready to install the mod, but first, check that everything is working and log in with the new profile. Create a world, quit, and look in your new
.minecraft/aether2/saves/ folder to make sure your worlds with this profile are saving to this folder instead of the main
Now mod away! When the mod instructions tell you to do something to
bin/minecraft.jar, just do that to
versions/aether2/aether2.jar instead and it will work the same. When an instruction tells you to put a file in your
coremods/ folders, put them in
minecraft/aether2/coremods/ folders instead.
And watch for that tricky dot in
.minecraft. All modding instructions (including most of my own here) will tell you about your
.minecraft folder, but on OSX it's missing the dot. This is normal and not a problem, unless you let it confuse you. This is just an odd difference that Minecraft has on Mac OS X that you have to get used to.