It’s spring time and like many people I’m sucking down air conditioning, but I decided to take a look at how one of my PC’s is using electricity like it’s an all you can eat buffet. Here’s some information about my current HTPC that is relevant:
- Intel Pentium Dual Core
- Gigabyte/Intel G31 motherboard
- GeForce 8400GS PCI Express
- WD Caviar GP 750GB (variable RPM)
- Windows Vista Home Premium
- Runs all day
If you live in the US visit the Energy Star website, there is tons of good information on there already. Generally most monitors have been Energy Star compliant for a while but it seems a lot of PC’s are compliant as well these days – this is good since people generally have more PC’s than refrigerators.
I’ve never really found a great description for a lot of the advanced power options in Vista so I decided to blog about them after doing some research.
The default options are pretty self-explanatory, but the quick-details are that balanced and power saver throttle your PC while it’s idle and will eventually put your computer into sleep/hibernate – while high performance does neither. For my HTPC none of them are sufficient so I decided to create my own profile that throttles and never sleeps (like me!)
I set these options to never; the defaults for these are very reasonable for normal usage however.
Sleep – often called standby or the S3 state by those familiar with the ACPI spec, turns off all fans and disks and puts your CPU into its lowest power state while keeping the RAM powered on so it can wake up quickly from a user or system event - like Wake on LAN.
Turn off hard disk after – Turns off a disk until it is accessed by a write or read operation. If you have disks in your systems that are not used all the time, for example you have a secondary drive with movies that is only used every Saturday. I have a single system disk so I set this to never.
Wireless Adapter Settings – Allows your wifi adapter in cooperation with the access point you are connected with to periodically enter a low power state when there is a lack of network traffic. Unfortunately when Microsoft was testing this power option, it was determined that not enough hardware routers correctly supported this feature and it would end up causing connectivity issues – so the default is “Maximum Performance”. If you use wireless on a laptop it’s definitely worth your while to try “Low Power Saving” option because it can save a significant amount of battery as you do things like browse the web which may not require significant amounts of network traffic – more information on Vista team blog. You may also need to make sure that power management is enabled in device manager for your wireless adapter.
USB selective suspend – USB 2.0 allows devices to enter a low power state by placing the port into a suspended state when it’s idle – this is determined and managed by the driver. The system can wake up the device to respond to an event, or the device can wake itself up as well if supported – this is called Remote Wakeup. USB selective suspend also requires that the corresponding USB Root Hub has power management enabled in Device Manager (as well as the device if applicable). Power savings and stability vary based on type of device, usage, and how well the drivers are written – another good reason to buy things from reputable chipset and device manufacturers since they are more likely to support these kinds of advanced features.
PCI Express Link State – PCI Express uses a series of high speed links (up to 16x Rx/Tx) to exchange data, even when there is no data traffic there is still data being exchanged in order to have synchronization. PCI does not suffer from this issue since it is parallel, and has a much smaller overall pipe anyway. In order to save power devices have the ability to turn off these lanes temporarily - synchronizing them when they come back. It’s unclear to me at this point which PCI Express devices support this (I’d like to find out more about this), here’s what I do know:
- Supported in PCI Express 1.1 devices
- Potential savings are significant for devices with 8x lanes or higher
- Requires a compatible motherboard chipset/bios, device, and drivers
Conclusion
There is a wealth of links I’ve gotten this information from and tried to reference above anything that was particularly juicy - a lot of the information above assumes you already know basics. This is a good summary of the things I’ve read and it answered a lot of my own questions about what these settings do, sometimes answers lead to more questions though. My expectation is that this information is difficult to find because it’s over the head of the average user and support can vary greatly between hardware. If you have any valuable feedback on a particular setting, or questions please ask.
June 15th, 2009 at 06:04:04 AM
All the extra services you'll never need are still chewing up cpu time.
