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Let's consider the following situation. There is a server, for example supermicro, that has 4 USB2 ports, 4 USB3 ports, and 2 VGA ports. At the same time we don't use these ports, I mean there are no devices connected to them. Do these ports consume any power in such a situation? I am asking as I need to understand if these ports draw any power from power supply.

Pavel_K
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  • What do you need to know it for, or is it just curiousity? – pjc50 Apr 21 '20 at 23:02
  • For your particular system it should be easy to determine it experimentally. Measure the input power for an idle system, and then disconnect VGA and all USB, and see if any difference will follow. – Ale..chenski Apr 22 '20 at 02:54
  • @pjc50 No, no curiosity. I need to know if I should take these ports into consideration when I use power supply calculator. – Pavel_K Apr 22 '20 at 08:12
  • What "power supply calculator"? – Ale..chenski Apr 22 '20 at 17:40
  • @Ale..chenski This one https://seasonic.com/wattage-calculator – Pavel_K Apr 22 '20 at 18:00
  • Oh, I see... For this purpose you can safely ignore USB controllers and internal VGA. The entire "calculator" looks like a goofy marketing tool, since core consumption varies wildly with load up to processor(s)TDP, and add-on PCIe video cards can consume hundreds of watts. Counting keyboard/mouse consumption is silly on this background. – Ale..chenski Apr 22 '20 at 21:47
  • @Ale..chenski Thank you very much for your explanation. – Pavel_K Apr 22 '20 at 22:05

4 Answers4

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USB, no. VGA? Very definitely draws power even if no display is attached - though it may go into a lower-power state. This would be very controller - dependent.

hacktastical
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The answer depends on the level of implementation of ACPI system states in your particular system. Each device on a computing platform also has special device power states within ACPI:

From NCR website:

ACPI defines power states for peripherals which are separate from the system power state. The device power states range from D0 (fully-on) to D3 (off) It is the responsibility of the driver developer for each peripheral to define and support the available power states.

There is also some extension to Sleep States called "Modern Standby", some improvement over "connected standby".

If your system supports Intel-defined so-called "S0ix" mode, and all peripheral controllers (and their drivers!) are compliant, the USB host controller will be forced into D3 state if nothing is connected to it. Even if HID devices are connected, the system will selectively suspend them after some period of inactivity, and put host controller[s] into D3.

All these complications are invented mostly to prolong battery life of laptops, tablets, and phones. Implementation of low power saving modes is pretty complicated and requires additional embedded management processors into main computing cores, and it takes some toll. It is quite unlikely that your server system supports them.

Ale..chenski
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The USB ports themselves don't draw any power when there are no devices attached, but the USB controller for those ports is using a small amount of power to maintain a "presence" in the system and to be ready to communicate when any device is plugged into a USB port.
VGA typically remains active and uses some power, but the amount of power used may depend on the BIOS settings, the OS settings (resolution, activity, power management/savings), the card/adapter itself, and the motherboard.

Edin Fifić
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The host controllers will draw a very small amount of power, yes. Probably in the region of milliamps.

pjc50
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