Herbie Murray
When a Mac goes to sleep, the system saves its state, including which apps are open, and saves documents in supported apps. This prevents data loss in case the battery is depleted. The Mac can then be resumed from where it was left off. However, the clock could jump between any two instructions in an app, which may be noticeable if the app is interacting with external systems. Terminal processes like Python scripts will stop execution when the machine goes into idle sleep. To prevent this, the built-in tool 'caffeinate' can be used, which prevents the machine from sleeping until the program is cancelled using ctrl+c.
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What You'll Learn
- Apps are suspended, but can be resumed at the point of interruption
- The Mac saves its state, including which apps are open, and saves documents
- The processor enters a low-power mode, and disks spin down
- Video output is deactivated, and displays are turned off
- Bluetooth and other functions are deactivated to save battery
Apps are suspended, but can be resumed at the point of interruption
When a Mac goes to sleep, all applications are paused, and the processor enters a low-power mode. However, the system clock continues to run, and the Mac may still exhibit some activity, such as push notifications, power management, and network activity.
Upon waking a Mac from sleep, the system resumes exactly where it left off, allowing users to continue their tasks from the point of interruption. This is made possible by the Mac's safe sleep feature, which saves the system state, including open apps and documents in supported apps, before entering sleep mode.
The transition to sleep mode can occur at any moment, and the system clock can leap forward by a significant amount. This can cause issues for apps, especially those interacting with external systems or performing time-sensitive tasks. However, the app developers can address these challenges by implementing appropriate coding practices.
To prevent a Mac from falling asleep at an inopportune moment, users can utilise tools like Caffeine or the built-in 'caffeinate' command in the Terminal. These tools allow users to specify commands or processes that should not be interrupted by sleep mode, ensuring the Mac remains active until those tasks are completed.
While sleep mode is not mandatory, it offers benefits such as locking the Mac for security, saving power, and providing a quick resume when compared to a complete shutdown. Additionally, with the default hibernatemode 3, the Mac stores a copy of memory to the disk and keeps the RAM memory powered during sleep, allowing for a faster wake-up process.
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The Mac saves its state, including which apps are open, and saves documents
When a Mac goes to sleep, it saves its state, including which apps are open, and saves documents in supported apps. This prevents data loss in case the battery is depleted. The next time the Mac is started up, the saved state will be loaded, allowing the user to pick up where they left off. This is known as the safe sleep feature, and it is the default on portable Macs released after 2005.
Safe sleep is also called "hibernatemode 3". In this mode, the RAM remains powered on during sleep, allowing for a quick wake-up process. When awakened, the Mac reloads the memory, unless it has run out of power, in which case, the hibernate image is reloaded. This mode was designed to save battery charge, and a MacBook with a fully charged battery can remain in standby mode for up to 30 days.
There are different sleep modes available for Macs, and while the default mode is recommended for most users, it is possible to manage and change these modes using the Terminal app. For example, "hibernatemode 25" can be set using the pmset command in Terminal. In this mode, the Mac saves what's in its memory to disk and then powers down the memory. As a result, both sleeping and waking are slower, but this mode further saves battery life.
Additionally, there are tools available to prevent a Mac from falling asleep, such as Caffeine, which can be used to keep the system awake for a specific period or until a certain process is finished.
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The processor enters a low-power mode, and disks spin down
When a Mac is suspended, the processor enters a low-power mode, and the disks spin down to save power and extend battery life. This is done by putting the drive into idle mode and setting a standby (spindown) timeout. The timeout value determines how long the drive will wait (with no disk activity) before turning off the spindle motor to conserve energy. Values for the timeout can range from 5 seconds to 5.5 hours, or even up to 11 units of 30 minutes, resulting in a timeout of 5.5 hours.
There are various power plans available on Mac, including Balanced, Power Saver, and High Performance. The Power Saver setting slows down the computer significantly but saves power and extends battery life. This is ideal for situations where the user is browsing the internet or listening to music. On the other hand, the High-Performance setting maximizes CPU and graphics card usage, making it suitable for gaming or high-intensity tasks.
Additionally, there are different hibernation modes available on Mac, such as hibernatemode 3 and hibernatemode 25. The default mode for laptops is hibernatemode 3, where the Mac stores a copy of its memory to the disk and keeps the memory powered during sleep. When awakened, the Mac reloads the memory unless it has run out of power, in which case, the hibernate image is reloaded. Hibernatemode 25 can be set using the pmset command in Terminal, and it saves the Mac's memory to disk before powering down. As a result, both sleeping and waking times are slower, but this mode further conserves battery life.
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Video output is deactivated, and displays are turned off
When a Mac is suspended, it enters sleep mode. This mode will turn the screen off and lock the device, preventing unauthorised access. Sleep mode also allows users to resume their work instantly, as it saves the current session and keeps it in memory. This means that when the Mac is awakened, it can pick up right where it left off, with all apps and documents remaining open.
Sleep mode is particularly important for laptops, as they need to save energy to protect the battery. In addition to deactivating video output and turning off displays, laptops will also deactivate the Ethernet port, built-in modem, AirPort functions, and limit the functionality of USB ports.
The default behaviour for Mac displays is to save power when possible. Depending on the model, the display may be put to sleep first, or the display and computer may sleep simultaneously.
Sleep mode is not the same as hibernation mode, in which the RAM is powered off. Sleep mode keeps the RAM powered on, allowing for a quicker wake-up process.
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Bluetooth and other functions are deactivated to save battery
When a Mac goes to sleep, it does a lot more than just resting. There is CPU activity, push notifications, power management, and network activity that continue to run in the background. This can impact battery life, so certain functions are deactivated to save power.
One function that is deactivated is Bluetooth. By default, macOS does not include a built-in option to disable Bluetooth when the device is asleep. However, there are third-party applications and scripts that can be used to achieve this. One such application is Bluesnooze, which is free software designed for macOS Monterey and up. Bluesnooze turns off Bluetooth when your MacBook goes to sleep and switches it back on when it wakes up. It also provides options to hide the icon from the menu bar and turn off Bluetooth when the Mac shuts down.
To manually disable Bluetooth on a Mac, you can use the terminal command "blueutil" to confirm the necessary permissions and create specific scripts to run when the device sleeps and wakes up. This method requires basic knowledge of the terminal and involves creating and editing specific files.
By deactivating Bluetooth and other functions during sleep, macOS aims to optimize battery life and prevent data loss. The system saves its state, including open apps and documents, to prevent data loss in case the battery is depleted. With hibernation modes, it can also manage power efficiently, ensuring a quick return to work when the device is awakened.
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Frequently asked questions
Your Mac apps are constantly suspended and resumed due to context switching. The clock could jump between any two instructions in your app, though usually not in a noticeable/significant way.
Yes, you can use the built-in tool called caffeinate. If you precede the terminal command with caffeinate, it will not sleep for the length of this particular command. For example, caffeinate python.
Your Mac does a lot when it is asleep. There is CPU activity, push notifications, power management, and network activity.
