Difference ESP01/01s and ESP8266 NodeMCU/D1 Wemos
ESP01/01s does not have the CH340C USB to UART component that uploads the Arduino IDE sketch compiled in binary from PC’s local storage to ESP01/01s external flash memory (512Kb or 1MB via PC’s USB port.
External Flash Memory (ESP01/ESP01s)
512 kb / 4Mbit (ESP-01)
1 Mb / 8Mbit (EPS-01s)
Note: New ESP01 maybe shipped with 1 Mb / 8Mbit
ESP01/ESP01S Pin Out
Blue LED (built-in aka Comm LED)
The blue LED is on TX line (GPIO 01). Serial.println() in your sketch will NOT work at same time.
ESP8266 Wifi Community