It's so variable simply because of the modular nature of the editor. If you use a 60 byte javascript file, you are going to see more resource usage in Atom tha

It's so variable simply because of the modular nature of the editor. If you use a 60 byte javascript file, you are going to see more resource usage in Atom than you would with the 60 byte C file, that's because by default atom includes more "javascript oriented" plugins, so it will be analyzing the file more. I currently have 83 (holy shit I didn't know I even amassed that many!) plugins in my atom editor. If I open a JS file it's doing a LOT to that file. Linting, formatting, searching for symbols to autocomplete, searching for paths to autocomplete, looking for things that look like color hex codes to highlight in that color, trying anything that looks like a link to see if it can show a hover-preview for them, etc... If I open a C file in Atom, it's going to syntax highlight it, and nothing else. Then it's further made harder because some of those plugins will stop working on files of specific sizes (ex my intelligent autocomplete package will stop working somewhere around 1mb I believe), so you might even see it drop in memory usage after that.