Unicode and ASCII are two ways of encoding characters by representing them in binary so that you can easily write, store, transmit, and read them in digital media. One of the major differences between the two is the way characters are encoded when you use each method. Another difference can also be noticed in the number of bits being used by each method.
Initially, the total number of bits used by ASCII to encode a single character is seven bits. However, this has been changed to 8 in order to make it more efficient for character encoding. On the other hand, the total number of bits that will be required to encode each character when you use Unicode is not the same as that of ASCII as you can choose to use between 8 bits, 16 bits, and 32 bits. As a result of this, Unicode seems to be a better choice if you want to encode a huge number of characters at a time.