Prism Launcher Java & JVM Configuration
Match the exact Java runtime (Java 21, Java 17, or Java 8) to your Minecraft version, tune min/max RAM, and pass GC JVM arguments.
JVM Arguments: Aikar's Flags, G1GC & Generational ZGC
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Custom garbage collection flags smooth out 1% low frame drops when generating chunks in 300-mod packs. Applies to Modded 1.12.2 – 1.21.4+.
- Configuration
- JVM Arguments: Aikar's Flags, G1GC & Generational ZGC
- Minecraft Range
- Modded 1.12.2 – 1.21.4+
- Recommended Build
- Prism Launcher Java Settings → JVM Arguments
- JVM Flags
- -XX:+UseG1GC or -XX:+UseZGC -XX:+ZGenerational (Java 21+)
Why JVM Arguments: Aikar's Flags, G1GC & Generational ZGC matters for Modded 1.12.2 – 1.21.4+
Custom garbage collection flags smooth out 1% low frame drops when generating chunks in 300-mod packs.
Inside Prism Launcher, open **Settings** → **Java** (or override per instance under **Edit Instance** → **Settings**) and click **Auto-detect** or **Download** to select `Prism Launcher Java Settings → JVM Arguments`.
Recommended JVM flags and memory checks
- **JVM arguments:** `-XX:+UseG1GC or -XX:+UseZGC -XX:+ZGenerational (Java 21+)`. Always click **Test** in the Java settings panel to verify the runtime passes Prism's architecture check.
- **64-bit verification:** Ensure the architecture column reads `x86_64` (or `arm64`), never 32-bit `x86`, so you can allocate more than 2 GB of RAM.
- **Download launcher:** Get the latest Windows build of Prism Launcher from /download.
Frequently asked questions
Which Minecraft versions need JVM Arguments: Aikar's Flags, G1GC & Generational ZGC?
It is designed for Modded 1.12.2 – 1.21.4+.
Can Prism Launcher keep Java 8, Java 17, and Java 21 installed at the same time?
Yes. Prism Launcher lets you assign a different Java executable to each individual instance.
Get Prism Launcher
Windows, macOS & Linux
Free and open source. Sign in with the Microsoft account that owns Minecraft, then create your first instance.
