SIMILARITIES
Some similarities are that for linear and non-linear systems of equations, you need the same number of equations as unknowns to solve the system and find the only solution for each variable.
DIFFERENCES
Some differences are
The linear system of equations has degree "1" in each of its variables.
The non-linear system of equations has degree "n" in each of its variables.
where n = 1,2,3, ..., i, ..., n.