So far, we have mostly ignored the limitations imposed on a computer by the size of its memory. An idealized universal computer has an infinite memory, but a real computer’s memory is limited, usually by expense. As long as the size of the memory is adequate for the task at hand, we are free to ignore the limitation, but some memory-intensive algorithms and applications store such large amounts of data that the amount of memory available becomes an important consideration. Applications that manipulate representations of the physical world—such as images, sounds, or three-dimensional models—are often memory-intensive. Knowing how much memory is required for a given application is important not only in judgments about whether or not the computer is big enough to handle it but also for estimating the time required to process the information.