The ESP-01 and ESP-01S are both compact and powerful WiFi modules developed by Espressif Systems. These modules are widely used for Internet of Things (IoT) and wireless communication projects due to their low power consumption and high level of integration. While both modules are based on the ESP8266 chip, there are a few key differences between the two. The ESP-01S includes an additional 1MB flash memory, providing more storage space for program and data storage. This makes it a better choice for projects that require larger amounts of code or data to be stored on the module. Both modules can be programmed using the Arduino IDE, making them easy to work with for developers familiar with the Arduino platform. They also support a variety of communication protocols, making them versatile for use in a wide range of applications. Overall, the ESP-01S offers improved storage capacity compared to the ESP-01, making it a suitable choice for projects requiring larger amounts of data and program storage.