These are mighty strange cables for a PC man like myself

So I have these fat cables:
They fit in the connectors of the routers on the front of the cpu modules:
But which cable goes to which port? And how many? All 6? I only have 4 cables.
Next on back there are some more stuff. Power cables were easy to no help needed there.
But there is this long cable labled "A B" on one end, then it forks to "A" and "B" looks like SCSI of some sort on the forked ends:
Then there is this terminal module:
I am guessing these are serial ports that go to the DB9 serial ports on the modules.
But there is one RJ style port and a DB25 port on the side, what are those? The DB25 says display, but what kind? Certainly not VGA.
I hope you guys may shed some light on this.