  The paper is devoted to studying the orthogonality graph of the matrix ring
over a commutative ring. It is proved that the orthogonality graph of the ring
of matrices with size greater than 1 over a commutative ring with zero-divisors
is connected and has diameter 3 or 4; a criterion for each value is obtained.
It is also shown that each of its vertices has distance at most 2 from some
scalar matrix.
