The above HINT graph shows what happens if we just increase the clock speed keeping all other system configurations the same. An increase in clock speed reduces the runtime of a program. We wonder, what does it really mean to the actual user? Will applications of different sizes have same speedup? The answer is NO.
From the graph it is clear that increase on the left end of the curve will be higher than the right end of the curve. So small applications, which fit in the cache, will have a larger speedup compared to larger applications which do not fit in the cache. This difference is due to cache/memory miss rate and miss penalty coming to play with the large applications.