"delayloaded" functions are accessed via a lookup function stored at "lib/tools/delayLookup.lua".
Unfortunately the result is only stored in an internal cache but not in the library table.
That means the lookup function is called whenever the delayloaded function is accessed.
And since the lookup function is weakly stored it has to be reloaded every few calls.
That causes a lot of HDD accesses.

Examples
This shows the result is not stored in the library table:

lua
>=term.screen
function...
>=rawget(term, "screen")
nil

This causes a lot of HDD interaction:

local term = require("term")
local event = require("event")

while true do
 local e, s = event.pull(0.1)
 if s == term.screen().address then
  print("...")
 end
end

Since I didn't write the delayed loading stuff I'm not sure how to progress here. I could go ahead and modify lib/tools/delayLookup.lua to write to the library table. But I'd like to get someone else's opinion before I create a pull request.