2000 Ford Focus SE 2.0 Split port

Hi,

I recently acquired a 2000 Ford Focus Se 2.0 Split Port with a blown motor in it. By
blown motor I mean, the number 3 cylinder shot a piston rod through the bottom
of the block and through my oil pan - according to my mechanic.

Although he couldn't answer me this;

When I buy a new motor, do I need to buy a new computer for it as well?

Also,

If I buy a used motor do I need to make sure that I buy the computer that went
with that motor or not?

I've been told that if I take it to the dealership where I live that they will either
replace the computer or they'll just "Flash the Bios".

Thanks,
Tyler M.