Actually there are fib computers, Photonic computers using light as the basis of there operation. There are also Electronic, Fluidic, Mechanical and Positronic computers. The benefit is that a Photonic computer will be immune to Electronic weapons or scramblers which are covered in the weapons and screens chapters.
Bis model computers have one extra "Cell" enabling them to run an extra process or practically in game to function with one extra console equivalent. This means that a bis model will have a slight extra edge when lending its power to managing consoles (and the tasks and equipment they are responsible for).
i haven't gamed this yet, but the idea is that a Ship's Computer can stand in for a member of the crew and resolve a task. Its not the same as the computer being AI but it allows "the ship" to run some of its own processes. So the ship's Computer could I think be given an order to make the Astrogation task and send the ship into jump.
The difference in T5 to other versions here is that the Ships computer is not a deciding or limiting factor in the capability of the Jump Drive. The Jump Drive is defined according to its own design factors and stage effects as well as the jump bubble design.
Also on the subject of the Model/0. The Model/0 has a base tech level of TL8 but using Stage Effects we can build a Model/0 at TL5. however the Experimental TL5 model/0 will have much more limited capabilities, suffering a -3 Mod to its rolls. using QREBS it will be bulkier, harder to use and less reliable than the base TL Model/0