KSP: Is the limit graphics, CPU or RAM?

[Wolf Baginski]

Things have changed a lot since some of the answers to this sort of question that have popped up on Google. We have, for instance, 64-bit versions of the program, which means RAM limits are less of a problem.

First, what are the problems?

I don't recommend having less than 8GB RAM. This old machine I bought as an upgrade had 6GB, for arcane reasons,  and that didn't need to Swap to HDD, but I have upgraded. 4GB may still be enough for an un-modded install, but 8GB gives you a margin. Remember the OS and whether you might need to run a web browser to look something up. KSP isn't bad for memory use.

KSP is also pretty light on graphics. I'm still way behind the curve, but hardware prices are still dropping. I am using an nVidia 750 which is fine, but good luck finding a real one. Prices have dropped enough that the current nVidia 1050 is a plausible option for me. For what else I do the 750 is marginal, but it's OK

What I have seen is that KSP does a huge amount of floating-point math in the CPU for the orbits. And a big craft with a lot of parts is the problem. The old data on this is that Unity didn't take advantage of multiple cores, it just maxed out a single core, and that was the bottleneck

So can Unity genuinely use multiple CPU cores? If it doesn't, it makes current benchmark tests rather misleading.(Multiple cores was the answer, I remember being told, but some software still doesn't take advantage of it, and I know it's not always easy.)

 

(Arcane reasons: most computers arrange RAM in two channels. This machine uses three, but works with two.)

[Lisias]

The limit is Unity.

(more) seriously now:

If you have a embedded GPU, you need to account the KSP needs and the GPU needs. So, in order to support a installment that would run on a 4GB RAM using a discrete 2GB RAM VideoCard, your mainboard needs to have 6GB of RAM.

4GB is barely  enough on a vanilla installment on 1.4.3. Add to it the Mission Builder, and things start to get ugly. My best guess is that KSP 1.4.3 with mission builder should need about 6GB of dedicated RAM for the CPU (so, 8GB of mainboard RAM if your GPU is embedded).

About the multicore thing... KSP multithreading model is adequate for the "vanilla" installment. But once you install mods, they start to "eat" cpu cycles while building each frame, and this slows down everything. Unity's Garbage Collector is far from top notch also, and this is the reason of the "stuttering" that plagues our installments.

Currently, KSP spawns a thread/core to each spawned vessel on your universe, so the bottleneck are your biggest vessels. If you have a 1000 parts vessel and 100 vessels with 10 parts, that 100 vessels will be calculated across your multiple cores, but the core handling that 1000 parts beast will delay everything - so, it's usually better to have fewer really fast cores than many slower ones.

Your GPU is the next bottleneck, but this can be settle up trimming your graphics settings and careful choice of visual enhancements.

Edited June 14, 2018 by Lisias
(sigh). typos.