Mainly ECC ram and I believe they're better at floating point calculations, but I'm not an expert. You can have multiple processors on a board too. Here's a high level explanation.

https://www.hp.com/us-en/shop/tech-takes/why-should-i-upgrad...

Here's Reddit's take

https://www.reddit.com/r/explainlikeimfive/comments/66vy2r/e...