[SIEW82] suggests as a rule of thumb that vertical microinstructions have lengths in
the range of 16 to 40 bits and that horizontal microinstructions have lengths in the
range of 40 to 100 bits.The terms hard and soft microprogramming are used to suggest
the degree of closeness to the underlying control signals and hardware layout.
Hard microprograms are generally fixed and committed to read-only memory. Soft
microprograms are more changeable and are suggestive of user microprogramming.