Even before recorded history, humans used various aids, such as pebbles and notched sticks, to keep track of quantities. By 1200, a(n)- calculator, called the abacus, had appeared in China. Devices such as the abacus require the operator to apply a(n) to perform calculations. In contrast, calculators, such as the Pascaline and de Colmar's Arithmometer, are designed to carry out calculations autonomously. In the 1800s, an English mathematician named Charles proposed to build a device, called the Analytical Engine that would operate using steam power. The design for this device embodied many of the concepts that define the modern computer. In the 1930s and 1940s, several computers were developed, including the Atanasoff-Berry Computer, Z3, Harvard Mark I, Colossus, and ENIAC. Most of these early computers used tubes, which paved the way for the architecture of first-generation computers, such as UNIVAC. Second-generation computers were smaller and less power hungry because they used . Third-generation computers were even smaller because they used circuits. The key technology for fourth-generation computers, including personal computers, is the .