Today Ars Technica reported that the PS4 uses 70W of energy while in StandBy mode, then correcting the statement, mentioning that standby energy consuption is just 10W, while it becomes 70W when the console is performing a download while in low-power state.
Such a radical power consumption increase while downloading surprised many, but the reason was actually explained a few days ago by Sony’s Senior Vice President and head of Business Unit 1 Masayasu Ito as part of an interview with the Japanese website PC Watch.
Ito-san explained that initially Sony attempted to have background download performed exclusively by the secondary sub-system ARM chip (as it was announced during the console’s presentation in February), in order to keep the main APU powered down, but that proved not to be fully possible.
The download process is too heavy for the ARM chip alone, so the Jaguar-based CPU of the main APU (Accelerated Processing Unit, that includes CPU and GPU) is called into action to do the heavy lifting and protocol processing.
That causes the power saving effect of the ARM chip to be diluted during that kind of heavier activity. While this is the situation with the present design, Ito-san specified that it could change with further iterations of the console’s design.