XP Fast Resume

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Windows XP has a feature similar to Fastboot that speeds the time it takes to resume normal activity in a computer that is in standby or hibernate mode. Standby and hibernation modes are most applicable to laptop users and are intended to conserve battery life. Instead of turning off a computer, the user has a choice of standby or hibernate. In the newest laptops running Windows XP, resuming from standby can take as little as two seconds or less. Standby is a low power condition from which the user can quickly resume work. When the system is in standby, the memory contents are stored in volatile RAM. When resuming, the operating system informs the computer devices of a change in state. Some devices must return to an active state ahead of others. Windows XP has sped the process by overlapping device initialization using a new algorithm that eliminates blocking interactions among key system drivers or with other system activities. This does not, however, eliminate all delays in resuming. Page faults, for instance, might occur that cannot be remedied until disks are completely initialized, or a delayed program might not be released until that program is allowed to continue. Further, device driver quality can sometimes slow the resume.

In hibernation mode, memory contents are compressed and saved to disk in the system hibernation file (\hiberfil.sys), and the computer is turned off completely. When the user resumes, these contents (desktop and applications) are restored intact. The contents of the hibernation file are read into memory and used to restart the system and associated devices. High-end laptops can return from hibernation in less than thirty seconds, although this is highly dependent on what was in memory at the time of hibernation.

Improving hibernation mode compression algorithms and overlapping compression with Direct Memory Access transfers to disk have heightened hibernation speed in Windows XP. Hibernation resumption also benefits from the Fastboot improvements, especially prefetching and changes to device initialization routines used in resuming. Note, however, that resumption times can vary considerably and consume as many system resources as booting the computer. If too little RAM is installed and/or large applications were running when the computer went into hibernation, it can take longer for the machine to resume.

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