What is connected standby?
Starting with Windows 8 and Windows 8.1, connected standby is a new low-power state that features extremely low power consumption while maintaining Internet connectivity. For a PC that implements the connected standby power model, the connected standby power state serves as the primary off mode for the PC—similar to the off mode that a smartphone enters when the user presses the power button. The Windows UI exposes the connected standby power state to the end user as the system "sleep" state.
Connected standby brings the smartphone power model to Windows PCs. A connected standby PC can instantly resume from sleep, and is always connected to the Internet. Apps in a connected standby PC are automatically updated while the system is in connected standby so that critical information—including email and messages—are already synced to the PC when the user turns it on.
Connected standby has multiple benefits to the user over the experience that traditional ACPI Sleep (S3) and Hibernate (S4) states deliver. The most prominent benefit is instant resume from sleep. Connected standby PCs resume extremely quickly—typically, in less than 500 milliseconds. The performance of a resume from connected standby is almost always faster than resuming from the traditional Sleep (S3) state and significantly faster than resuming from the Hibernate (S4) or Shutdown (S5) state.
Connected standby also keeps the Wi-Fi device turned on, but in a very low power mode. In this mode, the Wi-Fi device automatically searches for known access points and will connect to them according to the user's preference. This feature allows the system to maintain connectivity, even if the system is carried between home and work, the bus, or a coffee shop. An additional benefit is that the Wi-Fi device is already connected to the network when the user turns on the system. With connected standby, there is no more waiting to connect to a Wi-Fi access point and then waiting for email to sync. Wi-Fi is already connected and email is already synced and waiting for the user to turn on the PC.
With a constant Wi-Fi connection, a connected standby PC also maintains constant connectivity with the cloud. Communications apps, including Skype, Lync, and others in the Windows Store, notify the user in real-time of an incoming request or call while the system is in connected standby. Apps can also deliver push notifications to alert the user to news events, weather alerts, or instant messages.
The benefits of a constant Wi-Fi connection are also available for connected standby PCs that have a mobile broadband (cellular) connection and wired LAN/Ethernet connections. A connected standby PC automatically roams between all available network types, and favors the available networking option that is the cheapest and uses the lowest power.
Connected standby is the foundation of the modern mobile experience. Users have come to expect all of their electronics devices to instantly turn on, have long battery life, and always be connected to the cloud. All smartphones and the overwhelming majority of tablets support a sleep mode that is always on and always connected. Connected standby enables Windows PCs to meet and exceed the same customer expectations.
Connected standby is a screen-off sleep state. Any time the system has the screen off, it is said to be in connected standby.
While the system is in connected standby, it can pass through various hardware and software operating modes. For most of the time spent in connected standby, the hardware is in a low-power state and the software is paused or stopped. However, the system intermittently powers up to process an incoming email, alert the user to an incoming Skype call, or perform other app-related background activities.
Connected standby is very different from the traditional ACPI Sleep (S3) and Hibernate (S4) states.
The ACPI Sleep and Hibernate states completely pause all activity on the system when the processors are turned off. Activity remains paused until the user turns the system back on by pressing the power button, keyboard, or touchpad. Connected standby automatically pauses and resumes activity on the system while the screen is off to maintain connectivity and sync content from the cloud. The amount of activity is tightly controlled to help achieve low power consumption and ensure long battery life. However, the amount of system activity during each connected standby state can vary with changes in app activity due to the type of network connection or the amount of incoming data.
ACPI Sleep and Hibernate do not maintain connectivity on the network (Wi-Fi, LAN, or cellular). In these states, the networking devices are turned off until the user powers the system back on. (There are exceptions for wired LAN devices that support wake-on-LAN (WoL) patterns, but these patterns are typically enabled on desktop systems and not on mobile/battery-powered systems.) Connected standby keeps the networking devices powered on but in an extremely low power mode to maintain connectivity. The Wi-Fi device can automatically roam between networks that are preferred by the user and alert Windows to important network traffic.
ACPI Sleep and Hibernate completely pause all app, service, and driver activity when the processors are powered off. In contrast, connected standby allows apps, services, and drivers to keep running, but they run in a tightly controlled manner to save power and extend battery life. Windows Store apps get a few seconds every 15 minutes to run background tasks, but desktop applications are paused for the duration of the connected standby state. Email sync and tile updates are performed by apps that run in a controlled manner during connected standby.
The traditional ACPI Sleep (S3) state consumes 500 milliwatts or more of average power consumption to maintain memory in self-refresh and enable the platform to wake on user input. This gives the typical mobile system with a 45-watt-hour battery just under 100 hours of sleep time on a full charge. However, connected standby systems use low-power memory and power-optimized embedded controllers to consume less than 150 milliwatts in most configurations. As a result, the typical connected standby platform can stay in sleep for 300 hours on a full battery charge. This is three times as long as in the traditional ACPI Sleep state.
Connected standby has longer battery life than ACPI Sleep and, unlike ACPI Sleep, maintains connectivity. The user of a connected standby PC no longer worries about the battery-life tradeoff between Sleep and Hibernate, or about the differences in resume performance. With connected standby, the user can just shut the lid or press the power button and be assured that the system will enter a low-power mode and maintain connectivity—just like a smartphone.
The decision to build a Windows PC that implements the connected standby power model affects all levels of system design. Delivering the required low-power consumption, long battery life, and constant connectivity requires system planning and engineering. Starting with Windows 8 and Windows 8.1, all client versions of Windows support connected standby on capable hardware—on both ARM and x86/x64 systems.
Connected standby PCs typically feature low-power hardware that includes a power-efficient SoC (or chipset), low-power memory (DRAM), and low-power-capable networking (Wi-Fi, mobile broadband (MBB)) devices. A low-power system design forms the foundation of long battery life during sleep in a connected standby PC, and has significant benefits even when the system is in active use.
A capable PC is active and mobile during connected standby. Therefore, mobile connected standby PCs use flash memory (such as SSD or eMMc) for disk storage. An email can arrive at any time and can be safely saved to the disk if there is no possibility of disk damage from writes that occur during arm movements.