---
title: "Troubleshoot RAM Allocation (Minimum & Maximum Memory MiB) Errors & Exit Code 1 in Prism Launcher"
description: "Fix UnsupportedClassVersionError, Exit Code 1, and JVM heap errors related to RAM Allocation (Minimum & Maximum Memory MiB) (All Minecraft versions) in Prism Launcher."
canonical: https://prismlauncher.ink/java/ram-allocation-min-max-memory-slider-troubleshooting
updated: 2026-10-17
---

# Troubleshooting: RAM Allocation (Minimum & Maximum Memory MiB)

Step-by-step fix for Java version mismatches and JVM launch errors on All Minecraft versions.

## Facts (2026-10-17)

- **Target Runtime:** RAM Allocation (Minimum & Maximum Memory MiB)
- **Minecraft Target:** All Minecraft versions
- **Vendor:** Prism Launcher Settings → Java → Memory

## Diagnosing RAM Allocation (Minimum & Maximum Memory MiB) startup failures

If your instance on **All Minecraft versions** exits immediately after clicking Launch, open the **Minecraft Log** tab. An `UnsupportedClassVersionError` or `Incompatible magic value` means the instance is overriding the global runtime with the wrong Java version.

Follow our [RAM Allocation (Minimum & Maximum Memory MiB) reference](https://prismlauncher.ink/java/ram-allocation-min-max-memory-slider) to point the instance at a verified 64-bit `javaw.exe`.

## 3-step repair in Prism Launcher

1. Right-click the failing instance → **Edit** → **Settings** → **Java**.
2. Tick **Java installation**, click **Auto-detect** (or download via Prism), and choose **Prism Launcher Settings → Java → Memory**.
3. Click **Test** to confirm the runtime starts cleanly, then launch your world. Need a fresh launcher install? Visit [/download](https://prismlauncher.ink/download).

## FAQ

### What if clicking Test says 'Could not reserve enough space for object heap'?

You either selected a 32-bit Java installation or set Maximum Memory higher than the free physical RAM currently available on Windows.

### Should I check 'Skip Java compatibility checks'?

Only enable that toggle for special backported modpacks (such as GTNH Java 17/21 builds on 1.7.10); for normal packs, switch to the matching Java version instead.

## Related

- [RAM Allocation (Minimum & Maximum Memory MiB)](https://prismlauncher.ink/java/ram-allocation-min-max-memory-slider)
- [Prism Launcher Java & JVM Configuration](https://prismlauncher.ink/java)
- [How to Fix Minecraft Exit Code 1 & Exit Code -1 in Prism Launcher](https://prismlauncher.ink/howto/fix-minecraft-exit-code-1-prism-launcher)
- [Fix 'Java Compatibility Check Failed' or Wrong Java Version Popup](https://prismlauncher.ink/java/fix-java-compatibility-check-failed-error)
- [Java 21 (64-Bit) for Minecraft 1.20.5 & 1.21+](https://prismlauncher.ink/java/java-21-temurin-minecraft-1-20-5-1-21)

## Download

Free and open source: [Download Prism Launcher](https://prismlauncher.ink/download)

Markdown mirror: https://prismlauncher.ink/java/ram-allocation-min-max-memory-slider-troubleshooting.md