The Evolution Of CPU Processing Power Part 1: The Mechanics Of A CPU

How early microprocessors like the Intel 4004 work at a fundamental level and how they evolved.

SERIES LINK - youtube.com/playlist?list=PLC7a8fNahjQ8IkiD5f7blIYrro9oeIfJU In this multi-part series, we explore the evolution of the microprocessor and its astonishing growth in processing power over the decades. In Part 1, we learn about the first commercial CPU, the Intel 4004 and examine how it and similar early CPU's work at the fundamental level. During the mid-1960s a revolution in miniaturization was kick-started. The idea of packing dozens of semiconductor-based transistors on to a single silicon chip spawned the integrated circuit. It laid the groundwork for a complete paradigm shift in how modern society would evolve. In March of 1971, the commercial launch of a new semiconductor product set the stage for this new era. Composed of a then-incredible 2,300 transistors, the Intel 4004 central processing unit or CPU was released. For comparison, ENIAC, the first electronic computer built just 25 years earlier could only execute 5,000 instructions a second. But what made the 4004 so powerful wasn’t just its 1800% increase in processing power - it only consumed 1 watt of electricity, was about ¾” long and cost $5 to produce in today’s money. This was miles ahead of ENIAC’s, cost of $5.5 million in today’s money, 180kW power consumption, and 27-ton weight. In order to understand how a CPU derives its processing power, let examine what a CPU actually does and how it interfaces with data. For all intents and purposes, we can think of a CPU as an instruction processing machine. They operate by looping through three basic steps, fetch, decode, and execute. As CPU designs evolve these three steps become dramatically more complicated and technologies are implemented that extend this core model of operation. FETCH In the fetch phase, the CPU loads the instruction it will be executing into itself. A CPU can be thought of as existing in an information bubble. It pulls instructions and data from outside of itself, performs operations within its own internal environment, and then returns data back. This data is typically stored in memory external of the CPU called Random Access Memory or (RAM). Software instructions and data are loaded into RAM from more permanent sources such as hard drives and flash memory. But at one point in history magnetic tape, punch cards, and even flip switches were used. BUS The mechanism by which data moves back and forth to RAM is called a bus. A bus can be thought of as a multi-lane highway between the CPU and RAM is which each bit of data has its own lane. But we also need to transmit the location of the data we’re requesting, so a second highway must be added to accommodate both the size of the data word and the address word. These are called the data bus and address bus respectively. In practice, these data and address lines are physical electrical connections between the CPU and RAM and often look exactly like a superhighway on a circuit board. REGISTER The address of the memory location to