Memory hierarchy is a structured arrangement of different types of memory storage in a computer system, designed to optimize performance and efficiency. It typically consists of several levels, including registers, cache, main memory, and secondary storage. Each level has varying speeds and capacities, with registers being the fastest but smallest, while secondary storage like hard drives offers larger capacity but slower access times. The purpose of this hierarchy is to balance speed and cost. Faster memory types, such as cache, are more expensive and limited in size, while slower types, like hard drives, are cheaper and can store vast amounts of data. By using a combination of these memory types, systems can achieve better overall performance.