Math notes - how to store?

[ZZK]

Hello,

I'm studying for PhD in mathematics and since during my research I learn things from many areas, I have a lot of notes that are loosely connected with each other.

I have a problem with storing my notes. I setup MediaWiki with an addon for math formulae, but it is very slow and kills my server. I tried storing my notes on my hard drive in pdf files, but I keep forgetting what is in them and editing them is a pain (I need to find the corresponding file with .tex source code and edit it which is more time consuming, than editing the article in an online wiki). With .pdf files, I cannot visualy see conections between the files and I need to open each of them, to check if it is what I'm looking for.

How do you organize your notes so that you can make the most of them?