New power state called “Connected Standby”
- Windows coalesces all the timer and network requests, turns the radio on periodically to satisfy them, then goes back to very low power consumption.
- But because app requests are getting satisfied they are up to date as soon as you press “ON”
8 ways Windows 8 benefits the retail industry [MSDN Blogs, Oct 5, 2011]
7. Energy friendly – The tradeoff between instant-on for customer service and the constant consumption of power has been minimized. Now retail environments with any number of client machines can use the Windows 8 “Connected Standby” mode to ensure that devices are available for use instantly while using the least amount of power possible. This feature will even allow enterprise software updates to machines that are in a low power state.
Dr. Paul Jacobs, CEO of Qualcomm on the Wireless Future [Global Technology Leadership Conference at the University of California Berkeley's College of Engineering, Nov 18, 2011]
[24:10] Up to this point – I would say – tablets predominantly have been an iPad story. The Android tablets are out there. They haven’t been quite as successfull. But I think that will change, not just with the Android but also with Microsoft working on having Windows. So they are porting big Windows onto mobile phone chips.
And the interesting thing about that is now your Windows computer will act much more like a smartphone. So Microsoft spent a lot of effort implementing a feature that’s called ‘Connected Standby’ which means that when your PC goes to sleep it will go to sleep like a smartphone – meaning that power consumption goes down to very low and every so often it will blip up, collect your e-mail and your Facebook notifications, and whatever else it is that needs to update, and it goes back to sleep at very, very low power. And when you touch the screen, boom it comes on right away.
And that is going to be interesting because now you have a tablet with a full computing environment, on a full web, all the stuff that you would expect. So I think that’s going to be a very, very interesting thing. I’ve seen the form factors. There are extremely, extremely aggressive form factors that are going to be coming out when these Windows 8 launches happen. [25:30]
Steven Sinofsky, Julie Larson-Green, Antoine Leblond, Michael Angiulo, and Chris Jones: BUILD Keynote – Day 1 [Microsoft transcript for the press, Sept 13, 2011]
MIKE ANGIULO: ARM and SOC hardware combined. This is a Qualcomm ARM reference design, this is the one we showed at Computex, this is an 8660 Snapdragon. It’s hooked up to this debugging system here that’s measuring power really accurately. And what’s going on on this monitor is you can actually see the amount of power being used. It’s very low. The system is not off, it’s in a new power state called “connected standby” which is a really low-power idle state. You can see these little spikes that show up here. What’s going on is Windows is coalescing all of the timer requests and all of the network requests, turning the radio on briefly, updating the apps, and then shutting the radio back down. So, when I turn the system on, it turns on with one click — or two depending on if you have demo gremlins.
The system is on. You can see the power jumps right up. It’s an instant-on type scenariobecause it was never off. I can interact with the system here and you can see the power kind of changes as we’re rendering and we’re drawing on the screen. And then when I go to turn it off, I click it, immediately the power drops down. What’s going on right there is the apps get a chance to pack up their data and then it’s shutting down and it immediately drops back to idle. That’s the kind of system — yeah. (Applause.)
STEVEN SINOFSKY: I mean, when we talk about fundamental performance, that’s what we’re talking about. We’re actually taking the things that you’d experience like in phones, and we’re bringing that to the PC architecture at the base kernel level.
MIKE ANGIULO: And it’s one of the things that all of these SOC systems will be able to do. If you’re good to the understanding connected standby session, you’ll see the same power demo running on the Nvidia Tegra 3, we showed — it was nine months ago at CES was the first time we showed ARM booting at all. And all it could do is just boot Windows 8 up to the desktop in one touch.
Understanding Connected Standby [Microsoft Channel 9 video, Sept 14, 2011]
Your PC in a year: how Windows 8 will change hardware [TechRadar, Nov 16, 2011]
Microsoft uses words like ‘fresh’ and ‘alive’ to describe the future of the PC, especially when it’s talking about the Connected Standby mode that PCs using both ARM and low-power System On Chip (SoC) x86 processors will have. “It’s about the application experience,” says principal program manager Pat Stemen; “You want an app that’s fresh, that has connected content.
I don’t want to wait for it to download and I want it to show that fresh information when I turn on.” In fact the official name of PCs that support this is Always On Always Connected.
It’s also about consistent, consistently long battery life, he says; no more guessing how long the battery will last – you’ll know how much power the PC uses when it’s on and when it’s in Connected Standby, so you can accurately predict battery life.
Connected Standby is an “ultra-low power idle mode” implemented as a new level 5 ACPI modein the processor and it needs new hardware throughout the PC as well.
You need low-power memory (the kind of DRAM that’s been going into servers to save money because it doesn’t generate as much heat), low-power buses and devices and flash storagerather than a hard drive; that’s for speed as well as power saving, because the system can’t predict when the drive will be in use.
LIKE A PHONE:
Connected Standby stops using power much faster than today’s PCs
The Wi-Fi in Connected Standby PCs has to be much smarterbecause it’s on all the time, checking whether any of the network traffic matches the patterns of notifications that can wake the PC up – incoming VOIP calls or SMS and instant messages, for example.
That turns the whole PC back on so you can answer the call. Otherwise, the Wi-Fi connection periodically wakes itself up and collects data for the Metro apps that are on the Start screen.
That means putting a small processor in the Wi-Fi chipset and supporting NDIS 6.3, which lets the chipset do in hardware some of the network processing the PC would usually do in software; it also makes networking faster when the PC is on as well.
With Wi-Fi so important for Connected Standbyit has to get connected quickly; expect to get onto a hotspot or access point in about a second rather than the 12 seconds common now, even if you turn a PC off at work and turn it back on at home.
Tablets and a lot of notebooks will have built-in 3G next year. That’s going to use less power because new 3G connections will let Windows tell them when to turn off the transmitting radio because the PC is idle and just listen for incoming traffic, so the 3G card can go into ‘fast dormancy’ rather than keeping the radio on just in case (because turning the radio off saves power but turning it off and on again can use more power than leaving it on).
Knowing when to turn the radio off will stop 3G eating your battery
USB 3 will be on all these PCs too, not just for the faster speeds but because “it works better at low power,” according to Dennis Flanagan, who runs the team implementing Connected Standby for Windows 8. “It uses much less steady-state power when there’s nothing being used on the bus.”
But the two main ways of connecting peripherals will be peer-to-peer Wi-Fi, using the Wi-Fi Direct standard which lets your notebook get online and connect to a Wi-Fi-enabled device at the same time, and the lower-power Bluetooth LE.
Flanagan calls that “low-power wireless connectivity for longer battery life and for a new class of low power devices that can last two or four years on a couple of batteries”. Having NFC that’s cheap enough to put into all PCs helps here as well, because you’ll be able to tap Wi-Fi and Bluetooth devices against your PC to pair them instead of following on-screen prompts.
Smarter than Smart Connect
Intel’s Smart Connect mode, coming in second-generation ultrabooks and netbooks with Cedar Trail Atom CPUs next year, also aims to keep new PCs up to date when they’re in standby but it’s not as sophisticated as Connected Standby– and doesn’t need as much new hardware to work. “It keeps your PC always updated,” Intel’s John Wallace told us.
“When the device is in a sleep state it wakes up and pings network so it can download email and update content. Windows 8 is push, this is pull; we’re waking up periodically and pulling content.” The problem with that is the PC will wake up and connect even if there’s no new content to download.
“We’ll have true connected standby on next generation hardware that gets push notifications and wakes up,” Wallace predicted; that could be the Haswell chip that will be used in third-generation ultrabooks, if it’s delivered as a SoC.
With ACPI 5 and Connected Standby, Wallace says Windows 8 PCs will have “weeks of battery life” in standby. In 16 hours in Connected Standby a Windows 8 PC will use up no more than 5% of battery life; if that sounds an odd amount of time to measure, it’s what you get if you put your PC into Connected Standby at 5pm and pick it up again at 9am next morning.
Initially Connected Standby and Smart Connection are only aimed at tablets and notebooks. “Over time, Connected Standby may also scale to all-in-on systems and desktop PCs as well, although we’re not really focused on that right now,” Stemen explained.
Rapid Start and fast boot
The improvements we’ll see in all PCs next year are include faster boot and better security. Again, the Microsoft approach to starting up faster is more aggressive than Intel’s Rapid Start, which aims at taking less than seven seconds to resume from hibernation; PCs with Connected Standby will wake in less than 300ms and all PCs with UEFI BIOS will boot in six seconds(and Windows 8 will actively warn you of any software you install that slows that down).
That includes checking that no malware has tampered with Windows and turning on your anti-virus software before you bootto avoid malware lurking on any USB sticks you have plugged in.
UEFI means PCs can start checking for viruses before they start Windows
We have 3 goals in mind when engineering Windows 8 power management:
- Let the hardware shine. We built Windows 8 such that the power efficiency of the hardware platform shines through, regardless of whether the system is a SoC-based Windows tablet or an SLI-equipped gaming PC. We designed our power management interfaces in a consistent, standardized way across all platforms. This allows our hardware partners and application developers to focus on their unique innovations and experiences instead of the differences in platform hardware and power management.
- Continue to deliver great battery life. Windows 7 delivered a significant reduction in power consumption and increase in energy efficiency, particularly mobile PC battery life. (In fact, you can read how we thought about it in this e7 blog post.) In Windows 8, we want to maintain that same level of efficiency on existing PCs even as we re-imagine the rest of Windows.
- Enable the smartphone power model. One of the coolest things about the System-on-Chip (SoC) platforms you’ve seen us talk about at CES and //BUILD/ is their capability to quickly enter very low-power idle states. We want to leverage that ultra-low idle power to bring the constant connectivity and instant-on features of the smartphone power model to capable Windows 8 PCs.
How software influences power consumption
Software can influence power consumption by consuming resources—CPU, disk, memory, etc.–as each of those resources has a power cost associated. Software also influences power consumption through the OS and driver software responsible for managing hardware power states.
Windows 8 features 3 key innovationsto improve how software influences power consumption—the Metro style app model, idle hygiene, and a new runtime device power management framework. We will give you a brief overview of how these innovations improve power consumption in this blog post.
The Metro style application model
Most of us have experienced the influence of software on power consumption first-hand. It might be that you have an app on your phone that goes through battery quickly or you’ve heard the fan turn on in your laptop when playing a game or computing a spreadsheet. These are all examples of applications directly consuming CPU, GPU, network time, disk and/or memory.
One of the new power management innovations in Windows 8 isn’t a power management infrastructure feature; it is the Metro style application model itself. The Metro style application model is designed from the beginning to be power-friendly. The power management benefit is that the model makes it easy for developers to ensure their application is running only at the right time—applications in the background are suspended such that they do not consume resources and power when not in use.
Of course, we recognize that background activity is a critical component of apps that are always connected and responsive. The Metro style application model and the underlying WinRT support background activity through a new set of capabilities called background tasks. (See this Introduction to Background Tasks for more details.) Background tasks make it easy to perform background activity in a power-friendly fashion. They also enable developers to continue to deliver responsiveness and “freshness” in their applications, but the mechanisms are different than the existing Win32 model because of the desire for a fast-and-fluid interface and the other key attributes of Metro style apps (see 8 traits of great Metro style apps).
We’ve engineered background tasks and the overall Metro style application model to enable a new level of app responsiveness, while at the same time considering overall system attributes including power and memory consumption.
Software can have dramatic influence on power consumption even without consuming a lot of resources through intermittent idle activity. We refer to improvements to idle activity as idle hygiene.
Most PC platforms feature processor and chipset idle states that allow the hardware platform to stop the clock or completely turn off power to parts of the silicon when they are unused. These idle states are absolutely critical to enabling long battery life, but they require a minimal residency duration—that is, you have to be idle for long enough to make the transition in and out of the idle state worthwhile in terms of power used. This is because some power is consumed on the way into and out of the idle state. Software most effectively uses these idle states when there are as few exits from the idle state as possible, and the duration of the idle state is as long as possible.
We track the idle efficiency of Windows 8 using built-in ETW Tracing, some additions to the Windows Performance Analyzer, and a basic histogram. Below, you can see the difference in idle durations between Windows 7 and Windows 8. When the screen is on, we’ve already moved the bar significantly from a maximum idle duration of 15.6ms in Windows 7 to 35% of our durations longer than 100ms in Windows 8! With the screen off and during Connected Standby, our idle durations are even longer, currently in the tens of seconds.
Runtime device power management
PCs attain their longest battery life when all devices, including the processor, storage, and peripheral devices enter low-power modes. Almost every device in the modern PC has some kind of power management technology, and runtime device power managementdetermines how we use those technologies seamlessly without impact to the user experience. A really good example of runtime device power management is dimming the automatic display after a timeout in Windows 7.
Just to underscore how important device power management is, we have seen many systems where not enabling a single device’s power management features can easily reduce total battery life by up to 25%! (It’s worth noting here that disabling a device in Device Manager is almost equally bad—most devices are initialized by firmware at their highest power modes and require a device driver to get them to a more nominal power consumption.) You can diagnose some device power management problems using the built-in powercfg.exeutility in Windows 7 with the /ENERGY parameter. The output of /ENERGY is an HTML file that gives you a view of which devices and software are potentially running in a power-consuming state. Of course, using the factory image for your PC that came loaded with OEM and vendor-supplied drivers is almost always the best way to ensure the devices in your PC are well-behaved for power management.
Efficient power management of devices is performed by the driver for the device, in conjunction with the Windows kernel power manager and platform firmware. The power manager makes it easy for the drivers of these devices to implement their power management routines and coordinate any power state transitions with other devices on the platform.
For Windows 8, we’ve built a new device power framework that allows all devices to advertise their power management capabilities and integrate them with a special driver called the Power Engine Plug-in or PEP, designed for SoC systems. The PEP is provided by the silicon manufacturer and knows all of the SoC-specific power management requirements. This allows device drivers like our USB host controller or a keyboard driver to be built once, and still deliver optimal power management on all platforms from SoC-based PCs to datacenter servers.
We are hard at work with all of our ecosystem partners to deliver the low-power and long battery life technologies we all want in our Windows 8 PCs.