Memory

It is difficult to exaggerate the time difference between accessing memory and accessing disk. Although in human terms there is little perceptible difference between a 100-nanosecond write to RAM and a 100-millisecond write to hard disk, there is literally a factor of one million between them, comparable to the difference between 1 second and 10 days. The perceptible difference comes in repeated access, when the value of having enough memory quickly becomes clear.