“This update resolves some compatibility issues and reliability issues in Windows Vista. By applying this
update, you can achieve better reliability and hardware compatibility in various scenarios,” reads Microsoft's description of KB938194 which is offered in both 32-bit and 64-bit versions for the respective editions of Windows Vista Service Pack 1.
In the fall of 2007, the Redmond company issued two Vista compatibility, performance and reliability update packs that were essentially bits of the first service pack, but offered to Vista RTM users almost half a year ahead of SP1 via Windows Update. Following the availability of SP1, Microsoft informed that there are users who cannot implement the service pack due to a variety of issues, but mainly incompatibility problems. For them, the KB938979 and KB938194 update packages were reissued. Users of Windows Vista SP1 need neither of the packs.