The transistor count is the number of transistors in an electronic device (typically on a single substrate or "chip"). It is the most common measure of integrated circuit complexity (although the majority of transistors in modern microprocessors are contained in the cache memories, which consist mostly of the same memory cell circuits replicated many times). The rate at which MOS transistor counts have increased generally follows Moore's law, which observed that the transistor count doubles approximately every two years. However, being directly proportional to the area of a chip, transistor count doesn't represent how advanced corresponding manufacturing technology is, which is better characterized by transistor density instead (ratio of transistor count of a chip to its area).