This graph reveals the memory hierarchy in a computer system. Towards the left side of the curve, the problem size is small and it fits in the cache completely. Hence, the speed is maximum in this side of the curve. As the problem size increases (we move right), the data require more memory than the primary cache limit and hence one can see the sudden dip in the curve. Similar dip is observed when the problem size increases more than the secondary and main memory size limit.
Hence, a sudden dip of the QUIPS reveals the change in the memory regime of the system. Looking at the above graph, one can easily visualize a three-level memory (two level of caches and one level of main memory). A similar graph can be drawn using logarithmic memory on x-axis and QUIPS on y-axis. In latter graph, approximate cache and memory size can be easily determined using the sudden-dip-point and its corresponding x axis reading.