The ASCII standard has a couple of hundred symbols, where as the unicode set has tens of thousands of symbols - and in fact, the entire ASCII set is included in the unicode standard.
Izinga le-ASCII linezimpawu ezimbalwa, kanti isethi ye-Unicode inayo amashumi ezinkulungwane zezimpawu, futhi empeleni, lonke isethi ye-ASCII ifakiwe kuzinga le-Unicode.