The room-sized ENIAC of the late-1940s was the first electronic computer [1] . Its performance of 5,000 instructions per second at a footprint of 20 m2 and a cost of $5,000,000 (in present terms) contrasts with a smartphone's performance of billions of instructions per second at a footprint of 0.005 m2 and a cost of $500. The enormous computing power of modern processors results from the extraordinary miniaturization made possible through new technologies and expertise in chip manufacturing. The merging of computer hardware and software with net-based services through cloud computing and wireless networks is an ongoing development of mind-numbing complexity with great economic and social impact burdened by security and privacy issues.
More on how a computer works
Outfitted with 17,000 vacuum tubes, the ENIAC worked electronically and digitally, with reprogramming provided through rewiring. It was, however, not the first computer that could store and execute programs, a distinction attributed to the electromechanical and therefore much slower Zuse Z3 (see also Inventing the Computer).
The ENIAC was followed by a series of mainframe computers, initially still equipped with vacuum tubes, which were soon replaced with transistors and thereafter with integrated circuits. The groundbreaking personal computer then precipitated fast-paced development of modern laptops, notebooks, tablets, and smartphones. Ever more powerful processors drove the remarkable advancement, with impetus received from video gaming and new user-friendly software. Digital computers and electronic devices have almost completely replaced analog computing, though some control systems with sensors and actuators may still be best implemented with analog circuitry.