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I've always wondered if disabling devices via BIOS saves on power?

some full feature motherboard have all sorts of devices I never used. Firewire, built-in WiFi, audio (for my servers) and etc.

Thanks! :)

ps. I did a net search but nothing useful came up.

  • 1
    “I've always wondered if disabling devices via BIOS saves on power?” Depends on the make, model machine and even BIOS version. So this is all really subjective to setup. Voting to close as too broad. – JakeGould Aug 7 '17 at 22:07
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Yes, it does save power. If a device on your motherboard is enabled, it will draw power, even if it is not being used. Depending on the device and your power management settings, your OS may turn them off, or at least into a low power state.

As stated before, yes, you are using more power and memory. However, the amount is hugely insignificant compared to the use of the CPU, graphics cards, and even the fans.

Generally, if you arent using an onboard device, disable it in BIOS. This will prevent it from getting power at all. In addition to that, the OS doesnt have to load drivers for those devices, which uses a small amount of memory. But more importantly, in my opinion, you wont accidentally confuse one device for another, as it wont be visible to the OS.

Yes, you can leave them on with no detriment, but personally I say if its not being used, dont leave it enabled. You can always turn it on later.

  • 16
    Do you have any evidence for this? It seems highly unlikely that the power lines or even clock lines to a device are switched off, just that there's no communication with them. If the device power is low enough (in context) it doesn't really need power saving (especially on desktops where mains power is assumed). – Chris H Aug 7 '17 at 8:20
  • I can't vouch for PC systems, but on ARM SoCs that I work with, there are clock enables for each integrated peripheral. If your board is configured to never use say, the second SPI controller, then don't enable the clock for that peripheral. No clock means no switching, and no (or minimal) power consumed by that peripheral. – sawdust Aug 7 '17 at 8:44
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    @sawdust I believe you, but ARM devices are optimized for power consumption. What about x86? I agree with Chris that it does not seem likely it works like that there. – Stijn de Witt Aug 7 '17 at 9:24
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    @StijndeWitt -- Most, if not all, PC HW documentation is available only by NDA, so we're not likely to get an authoritative answer. But I would argue that adding a clock disable is easy in this age of high-density electronics (the power of the original IBM PC box can be had in a single chip for a few dollars!). What does this BIOS "disable" do? It seems to be more than info in a configuration memory. The HW seems to be actually disabled. Disabling its clock would do that, and save power. Two birds with one stone. – sawdust Aug 7 '17 at 9:39
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    “Yes, it does save power.” For all machines all setups and all configs? – JakeGould Aug 7 '17 at 22:11
8

It depends on the peripheral in question and the driver.

It's rare for the device to actually be powered off completely. More commonly, the device is placed into a low power sleep state and the BIOS does not report information about it to the OS.

The OS driver will most likely also place the device in a lower power state. So the question becomes, is the BIOS setting lower power than the driver setting.

In some cases they may be the same, e.g. for disabled GPUs, sound and serial ports. In some cases the OS may keep the device powered up to some extent, e.g. a network port that can detect when a cable is plugged in. It may also depend on if you disable the device or merely leave it idle in the OS.

It's likely the disabling the device in the BIOS is a fairly safe bet for low power, but it's also possible that the driver might contain newer, more up to date code that does a better job.

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    This is true IME for integrated sound cards at least. Speakers plugged in to a disabled sound card hiss in the same way as if the sound card is enabled but idle, and unlike an unpowered card. – Chris H Aug 7 '17 at 12:03
  • Interesting, although that could be because the outputs of the de-powered amplifiers are floating and just picking up noise. – user3241 Aug 7 '17 at 13:16
  • I would expect a different noise from a de-powered amp compared to one with no input (that wasn't what I was troubleshooting but I was intrigued) – Chris H Aug 7 '17 at 13:27
  • If the peripheral is disabled in the BIOS (a condition imposed by the question), then why/how would the OS detect this device and install a driver for it? – sawdust Aug 8 '17 at 21:35
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This is largely implementation-dependent. It's certainly possible to implement advanced power saving features in BIOS which would be unavailable on the OS level. It's also possible that the device disabled in BIOS will simply not be reported to the OS and remain in "uninitialised" state, similar to devices which you disable on the OS level.

Sometimes, a single IC implements several functions which are seen as separate "devices" by the OS (e.g. WiFi+Bluetooth adapters). For such ICs, the actual power consumption may vary depending on which combinations of devices are disabled, while disabling a single device may have no effect on power consumption.

  • "It's certainly possible to implement advanced power saving features in BIOS which would be unavailable on the OS level." Why? What can the BIOS do for power saving that the OS driver can't? – user3241 Aug 7 '17 at 13:15
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    @ゼーロ Hardware settings which cannot be applied without restart are usually only available in BIOS. Various clock settings come to mind. – Dmitry Grigoryev Aug 7 '17 at 13:26

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