The way it was explained to me was as follows:
The device with the greatest amount of computing power in a PLC/PC connection is the PC, so when I transfer a file to PC from PLC I am uploading. If I take that same PC and instead go onto the web, the combined total computing power that I am accessing is greater than my laptop or PC. So when I access a file I am downloading from the more intelligent or more powerful computing source. When I am connected to a PLC (even a small PLC network) my PC is considered to be more powerful/intelligent and I am downloading to the less powerful PLC.
The device with the greatest amount of computing power in a PLC/PC connection is the PC, so when I transfer a file to PC from PLC I am uploading. If I take that same PC and instead go onto the web, the combined total computing power that I am accessing is greater than my laptop or PC. So when I access a file I am downloading from the more intelligent or more powerful computing source. When I am connected to a PLC (even a small PLC network) my PC is considered to be more powerful/intelligent and I am downloading to the less powerful PLC.