The ESP8266 is the answer to “I want something with Wifi.” Surprisingly, there are a number of engineers and hobbyists who have not heard of this chip or have heard of it but don’t really understand what it is. It’s basically the answer to everything IoT to so many engineering problems that have plagued the hobbyist and commercial world alike.

The chip is a processor with integrated RAM, some ROM, and a WiFi radio, and the only external components you will need are 4 capacitors, a crystal and an external flash! It’s CHEAP, like $4/ea cheap! Or $5 if you want it on a nice, convenient carrier board that includes all these components. The power consumption is reasonable (~200mA)¹, the range is insane ~300m² without directional equipment, and a PCB trace antenna and ~4km if you want to be ridiculous.

The processor by default runs at 80 MHz but can go up to 160 MHz, it has ~80kB DRAM (Data RAM), and ~35kB of high speed IRAM (Instruction RAM).⁴ Yes, that means it uses a Harvard architecture. The IRAM is loaded at boot with whatever the user wants to keep on-processor, though the processor can run code directly off of the external flash at a lower speed.

Source: How To Directly Program An Inexpensive ESP8266 WiFi Module | Hackaday