Windows Vista and Windows 7 have a self-optimizing feature—called the boot prefetcher—that uses the disk I/O pattern from the previous boots to predict the I/O pattern of the next boot. To improve boot performance, the prefetcher predicts what data is required and reads this data from the hard disk before the data is actually required. This optimization can make it difficult to create repeatable performance results.
The prefetcher data is located at:
The prefetcher ReadyBoot data is located at:
I have these two folders on my freshly installed Windows 8 Consumer Preview, no upgrading involved.
The Hiberfile (new in Windows 8, not available when booting from a VHD) stores the resulting memory data that has been obtained through system initialization, such that on subsequent boots the data can be read in again instead of being initialized again. This allows Windows 8 to focus only on what it really has to focus upon boot, initializing your devices.
Initializing a session as well as the remaining I/O in the Windows 8 was left unchanged (or improved slightly), which is why prefetching techniques still apply to everything that's outside the Hiberfile. And well, if you are booting when your Hiberfile has been invalidated (hardware changes, updates or a full reboot), it will kick in the Prefetcher as well.
Bottom line: The hiberfile is an improvement, not a replacement.