Hollowtech is IIRC Shimano’s term for hollow forging of cranks, rather than BB (HT I was with an Octalink BB if memory serves).
Shimano uses a 24mm spindle with their external BB’s; these should also work with most external BBs except SRAM GXP which has a stepped spindle so the DS & NDS bearings are different diameters (I think). BB86/90 is the same width as a conventional threaded external BB but uses press-fit cups so the cranks are compatible.
BB30 uses a larger spindle and moves the bearings back inside the BB so it’s narrower than an external BB setup; various adaptors are available to fit 24mm spindle cranks to a BB30 frame but not the other way round. PF30 is the same width but uses similar bearing cups to BB86 rather than bog-standard industrial bearings, the advantage being that PF30 doesn’t need a machined metal BB insert unlike BB30 for carbon frames.
There is an increasing number of BB30/PF30 frames about, mainly XC hardtails (the new Jekyll is about the only long-travel BB30 bike I can think of). Confusingly, the Spesh road OSBB is identical to BB30, but the MTB one isn’t.
Does that clear things up any? 😛
Andy