FerriteCore

FerriteCore is a performance mod created by malte0811. A memory optimization mod that reduces RAM usage by optimizing block state storage and other internal data structures. As a performance mod it concentrates on frame rate, loading times, and memory use, and it has been downloaded around 60 million times, which puts it among the options players reach for in this space.

FerriteCore is built for players running large modpacks who keep hitting memory limits. It deduplicates blockstate and model data in memory, cutting RAM usage substantially in big packs with essentially no downside. It is approachable enough to drop into a world and use right away, with little setup required.

The mod is available for Forge, Fabric, NeoForge, and Quilt, so it fits a range of modpacks and launchers. It currently supports Minecraft 1.20.1, 1.20.4, and 1.21.1, spanning the 1.20.1 to 1.21.1 releases. It runs on both the client and the server, so on a multiplayer server every player who connects needs it installed alongside the server itself.

FerriteCore works particularly well alongside Lithium and Sodium. Because it ships for both Fabric and Forge-family loaders, it slots into most popular modpacks regardless of which side they are built on.

FerriteCore's only effect is lower memory use, so it can be added to virtually any pack without compatibility concerns.

If you are comparing options, similar mods include Memory Leak Fix and ModernFix. They cover comparable ground, so the right choice usually comes down to your loader, version, and the rest of your pack.