What is the difference between = = = and = = ?

output of "==" can be 1, 0 or X.

output of "===" can only be 0 or 1.

When you are comparing 2 nos using "==" and if one/both numbers have one or more bits as "x" then output would be "X" . However if use "===" output would be 0 or 1.

e.g A = 3'b1x0

B = 3'b10x

A = = B would give X as output.

A = = = B would give 0 as output.

"= ="  is  used  for  comparison  of  only  1's  and  0's  .It  can't  compare  Xs.  If  any  bit  of  input  is  X output would be X

"= = =" is used for comparison of X also.