Generally, S3 is faster to resume than S5, because suspend-to-RAM preserves memory while soft-off requires a full reboot.
What S3 and S5 are and how they work
ACPI defines multiple sleep and power-off states. S3 and S5 are the two most relevant for everyday use, affecting how quickly you can return to work after stepping away from the computer.
Before listing the differences, here is a quick primer on what the states do and how they affect speed:
- S3 — Suspend to RAM: The system keeps the contents of main memory powered so the active session is preserved. The CPU and most peripherals are put into low-power states, but RAM remains energized. Wake is typically very fast because the session data is already in memory.
- S5 — Soft Off: The system is powered down for real. Most components lose power (aside from a tiny RTC); there is no memory retention of the session. Rebooting requires a full power-up sequence, hardware reinitialization, and an OS boot, which takes longer.
- Other states exist, such as S4 (Hibernate), where memory is saved to disk to allow a power-off with faster resume than a cold boot but longer startup than a pure RAM suspend.
- Support varies by hardware and OS. Some devices handle suspend-to-RAM reliably, while others may wake slowly or fail when resuming from S3. Windows, Linux, and macOS implement suspend differently and may include features that blur the line (for example, Windows Fast Startup).
- Storage type matters: SSDs shorten boot and resume times; HDDs can lengthen the OS initialization during a full boot from S5.
Conclusion: For most users, S3 provides a much quicker resume than S5 because the session is kept in RAM and no full boot is required, though hardware, firmware, and OS implementations can affect actual times.
Practical guidance: when to use S3 vs S5
Choosing between S3 and S5 depends on how you use your computer and how much you value speed versus a guaranteed clean start.
- Use S3 when you want the fastest possible resume and you trust your hardware to reliably preserve the session in RAM. This is common on laptops and desktops that you use actively throughout the day.
- Use S5 when you plan to leave the system unattended for longer periods, or when you want a guaranteed clean start after updates, driver changes, or trouble-shooting. S5 avoids any risk of RAM corruption affecting the next session.
- Windows users should know about Fast Startup. It’s not a pure S3 state but a hybrid shutdown that speeds up boot by saving part of the system state to disk. On some setups, this can feel similar to resuming from sleep, even though it isn’t the same as S3.
- On Linux and macOS, suspend-to-RAM (S3) and full shutdown behave differently depending on hardware and power-management configuration. If suspend seems unreliable on a system, a full shutdown (S5) or troubleshooting steps may be preferable.
Conclusion: In everyday use, S3 is typically quicker to resume than S5, because RAM is still powered and the OS does not need to perform a full boot. S5 provides a true power-off state and a clean start, which can be desirable for maintenance, updates, or security considerations. Real-world timings depend on hardware, firmware, and OS configurations.
Summary
Bottom line: Suspend-to-RAM (S3) usually beats soft-off (S5) for speed, since the system can wake directly from memory. However, firmware support, drivers, and storage hardware influence actual results. If you want quick re-entry, favor S3; if you need a complete off-state for reliability or updates, S5 is the better choice, and features like Windows Fast Startup can further reduce boot times in certain setups.