So, what's going on our James Webb Space Telescope cleanroom webcam right now?http://jwst.nasa.gov/webcam.html
In this frame (see attached pic) - there are two things. Near center is a latticed black structure with scaffolding structure around it and shiny things inside it. This is the flight instrument module (called the ISIM) - and inside it are all four of our flight instruments!
On the left side is the IEC - the ISIM Electronics Compartment. This is essentially the hot stuff that goes on the cold side of the telescope. Among other things, it holds the instruments focal plane electronics and control electronics boxes which need to be in reasonably close proximity to the instruments themselves.
Other ISIM electronics reside in the spacecraft bus - the hot stuff on the hot side of the telescope.