Install Minecraft GregTech New Horizons

Install optimized Java version

Download OpenJDK java version matching your system architecture. Most probably you will go for x64 Windows destribution with .msi installer. OpenJDK8U-jdk_x64_windows_openj9_8u212b04_openj9-0.14.2.msi

Install it following the wizard guides leaving all settings default.

Install Minecraft Launcher

Download MultiMC launcher and unpack launcher files into directory of your choise. Run the MultiMC.exe, it will guide you through first time launch setup.

On Java decision step point the launcher to just installed OpenJDK version. Default path for it would be C:\Program Files\AdoptOpenJDK\jdk-8.0.212.04-openj9\bin\javaw.exe. Please point to javaw.exe manually, autodetect can choose wrong path.

Login into your Minecraft/Microsoft account by going to Profiles -> Manage Accounts -> Add Microsoft and following instructions. (It will ask you to follow link and input code and credentials. Loading bar is fake.)

Install GTNH Modpack

Download the 2.2.0.0 version of GT New Horizons (MultiMC package version).

In MultiMC launcher click Add Instance -> Import from zip. Click Browse and select just downloaded GT_New_Horizons_2.2.0.0_(MMC).zip. Click OK.

Update settings for the game instance

Right click on the game instance GT_New_Horizons_2.2.0.0_(MMC) and go to Edit instance. Select the Settings tab.

Check Memory checkbox and set minimum and maximum memory allocation depending on your available RAM.

GTNH recommends between 4GB and 6GB of RAM, use more with careful consideration and testing. Setting -Xms much lower than -Xmm can cause pauses whilst the garbage collector to try to get back down to the minimum.

Give 6G of RAM to the modpack, or the maximum you can allocate without saturating your PC (If you have 4 or less total, it will be hardly playable at all. With 8 total, assign 5-6GB). The minimum amount of RAM given should match the maximum amount of RAM given for optimal performance, to prevent overly aggressive garbage collection behavior. Allocating more than 8GB may cause issues, since the Java Garbage Collector gets worse with larger amounts of memory. Remember the rest of your system needs some left over memory as well.

4 GB = 4096
5 GB = 5120
6 GB = 6144
7 GB = 7168
8 GB = 8192

Check Java arguments checkbox and insert the following options into text area.

-d64
-XX:+UseG1GC
-XX:+UnlockExperimentalVMOptions
-XX:+DisableExplicitGC
-XX:MaxGCPauseMillis=80
-Dsun.rmi.dgc.server.gcInterval=2147483646
-XX:G1NewSizePercent=20
-XX:G1ReservePercent=20

Launching the game

Launch the game! It will take a few minutes to launch the game (3 to 5 minutes for me), longer for the first time.

(Be warned that it plays LOUD music on main screen)

More optimizations (optional, recommended)

Optifine can cause glitches on some systems but usually it's wrong settings if you get any glitches or crashes. So I do recommend to use this, contact me if you have any issues with it.

Download OptiFine mod 1.7.10 HD U E7. Click View mods -> Add -> Select downloaded optifine mod file (OptiFine_1.7.10_HD_U_E7.jar)

(Optional) Together with OptiFine loading screen with progress bar makes the game load slower. So if you prefer faster load to fancy loading screen deselect checkbox Better Loading Screen GTNH in mod list.

When the game is launched you will have to modify some graphics settings. Go to menu -> Options -> Video settings:

!!!DO NOT TOUCH Chunk Loading!!!
Render Distance: 10 is a good compromise between distance and performance, you can also try different settings here
Advanced OpenGL: Fast
Performance: 
    Smooth FPS: Try out what works best for you
    Fast Math: ON
    Fast Render: ON
    Smooth World: ON

Check if your PC uses the right GPU. Mine uses Integrated Graphics Card instead of Nvidia one by default which lowers performance significantly. The GPU used can be viewed by pressing F3.

Unlimited map edition (optional, recommended)

Journeymap shipped with the mod serverpack uses the Fairplay version. This prevents players from seeing into caves, and other entities such as monsters or players.

GTNH wiki about JourneyMap fairplay

Steps to use unlimited edition:

1. Remove JourneyMap from your client mods (View Mods -> Right click on JourneyMap -> Remove)

2. Download JourneyMap 5.1.4p2 (Hotfix Patch 2) Unlimited Edition for Minecraft Forge 1.7.10

3. Place the file in your client mods directory (View Mods -> Add)

Hate high FPS? C'mon install shaders! (optional)

In case you have a billion dollar graphics card you can install some shaders to make Minecraft look nice. Here is a guide. You will need to have OptiFine installed and running.

Sildur's Shaders downloads Feel free to install newer versions.

Useful links

Guide to optimizations for Low End PCs Many of them already included in this guide.

Server setup

GTNH Guides