Today's Patch Tuesday delivery from updates included a surprise for Windows 8 (and Windows Server 2012) users: a non-security-related patch labeled as Important. The patch replaces one of the most important system files in Windows, the Hardware Abstraction Layer driver, aka Hal.dll.
On my 64-bit test systems, the update was blandly labeled Update for Windows 8 Release Preview for x64-based Systems (KB2727113). An x86 version is available as well.
Clicking the More information link on the update page leads to this Microsoft Support article, with a title that's among the longest I've ever seen:
Article ID: 2727113
On a computer that is running Windows 8 Release Preview or Windows Server 2012 Release Candidate, the system may randomly stop responding (hang) when you work on multimedia or communication activities. This problem may occur during video editing, unified communications, or other multimedia activities.
This problem may occur because of an issue in the interaction between the state-machine driving dynamic tick transitions and the state-machine-driving clock rate changes.
To resolve this problem, install this update on the computer that is running Windows 8 Release Preview or Windows Server 2012 Release Candidate.
The update appears designed to resolve a nagging bug that has been plaguing some users of the Windows 8 Release Preview who are using hardware built around an Intel "Sandy Bridge" chipset. Rafael Rivera has done the best job of running it down. As he explained in this post on June 26:
To quickly recap, the operating system, for some users, at random, seems to slowly hang — one app at a time — eventually forcing a reboot. We know the issue was confirmed by Microsoft and has reportedly already been fixed in newer builds of Windows 8.
I've run into the bug myself on two or three occasions and encountered similar behavior on some systems in the Consumer Preview. It's annoying, but relatively rare.
Because this update is rated Important, it's installed automatically. If you're running Windows 8 with Automatic Updates enabled, the update should be installed within 48 hours. You can force the update by going to PC Settings, selecting Windows Update, and tapping or clicking the notice that shows how many updates are available to be installed. That in turn will enable a detailed information box showing which updates are available. Click or tap the Install button to kick off the update immediately.