Basically both the courses will lead you a degree of graduation level and in terms of higher studies or employment there does not exist any difference.
Looking at the cirriculam of the courses, you would notice a difference between the two in terms of their courses of studies. In B.Sc ( computer - science), you will have to choose other two subjects apart from Comuter - science and as such your combination would be Computer - science, Mathematics and Physics. You could have taken chemistry in lieu of Physics and keeping other two combination constant, you could have persued the course.
Now coming across BCS combination, you will have to undergo into the details of various subjects relating to various modules related to computers and in that way efficiency in this field can be enhanced.
Unlike the B.Sc ( computer - science) course, which is available in numerous colleges, BCS are taught in a few colleges and they even conduct written - test to select the candidates.