If you see s7otbxsx.exe in your Task Manager, respect it. It is the unsung hero of legacy Siemens communication. And if you are starting a new project, leave it in the past.
If your application cannot talk to the PLC, S7DOS will return cryptic hexadecimal codes. Here is a cheat sheet: simatic s7dos
A common misconception is that it stands for "Simatic S7 Disk Operating System" or a forgotten Siemens PLC model. Let’s clear that up. If you see s7otbxsx
: If the "S7DOS Help Service" stops, TIA Portal will fail to find any hardware. simatic s7dos