Garbage collection by default in Java 8 appears to be multithreaded. I know by watching my CPU core usage while playing an average game. All my cores were each getting at least 50% usage. In addition, when I disabled two of my cores in my BIOS and started a game, I noticed rather alarming FPS drops whenever garbage collection hit. Secondly, the loading of MC itself is surprisingly multithreaded. During the loading of all the mods by Forge, I saw all 4 cores pegged at 100%, and I noticed an increase in loading time when I disabled 2 of my cores. And those optimization arguments in the FTB Launcher? Those do not increase FPS. They appear to optimize the garbage collector even more for multi thread CPUs. With it on, I noticed lower average FPS, however my FPS stayed much more stable, especially during garbage collection.



Also, you CAN be GPU bottlenecked in minecraft. Just for kicks, I swapped out the r9 270 in my secondary build with an HD 5450(for reference, is about on level with sandy bridge/ivy bridge intel integrated graphics.)

My FPS dropped by a decent bit(20-30), and I noticed my GPU usage was pegged at 100%. So anyone with a low end laptop/desktop may not just be CPU bottlenecked, but GPU bottlenecked as well! Some(or all) of this data may seem obvious to some of you guys, but I just thought I'd post my findings.



P.S. These tests were done with my secondary rig, being an athlon x4 860k with an r9 270. My primary rig is currently out of commission.



P.S.S. And if anybody is wondering about that beginners guide to optimizing modded mc and getting started in general, I'm working on it! It's sitting on my secondary media drive as a text document.



AMD users with 3 or more cores, Optifine multicore rendering can do wonders for your FPS(We're talking up by 100-200 frames). This is only in the ultra version.