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Usually Windows Update does not take that much time to check what updates are available but this time I noticed that it took over 1 hour for it to check and return with information what updates it recommends to be installed. While at it I noticed svchost.exe using 25% of CPU load in Task Manager:

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I have experienced similar Windows Update delay once but it was for laptop where I have not updated Windows for over 6 months. I thought it's because there's so much updates that need to be found, compared and downloaded by Windows Update. Not the case with my current laptop where I updated every time they have update available.

I am using Windows 7 64-bit Enterprise

marked as duplicate by Ƭᴇcʜιᴇ007, Moab, Deltik, Simon Sheehan, RedGrittyBrick May 12 '16 at 8:45

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    Windows update varies in time to completion widely between updates. there are many many possible reasons why one check might complete more quickly than another. you would have to dig into the process to determine what it was doing (web IO, waiting on web responses, rebuilding the databases of updates and products, etc). – Frank Thomas Apr 26 '16 at 14:01
  • @Moab No it's not because high CPU usage is what makes my question different. But thanks for linking to that question. – Boris_yo Apr 27 '16 at 6:16
  • I have noticed (well, for now, just observed this on one computer), that recently "Windows Update" service got updated and now, instead of 25% cpu usage, can consume all available cores, resulting in 100% cpu usage. It is very good thing, because more people will notice problem and give feedback to Microsoft. – Andrei Dec 15 '16 at 8:15
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When you use ETW/WPR/WPA to check for the CPU usage during the scan you see that the CPU usage comes from wuaueng.dll!CUpdatesToPruneList::AddSupersedenceInfoIfNeeded which is called from wuaueng.dll!CAgentUpdateManager::FindUpdates. The AddSupersedenceInfoIfNeeded method is the slowest thing. This does what the name indicates and looks if the offered/installed Windows 7 updates are still needed or superseded (outdated/replaced by newer ones). This is very slow.

With the last Windows Update Client update from March 2016, the update search is faster.

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There are lots of reasons for Windows updates to take longer and use more resources. These depend on the hardware and software that you have installed, what updates were actually done recently (globally), the update server's occupation, the Internet connection, what else your computer is doing, how fragmented your registry is, etc.

With the amount of people that Microsoft has difficulty in helping their updates to work because it really gets stuck, even them would unlikely be able to provide you with an actual answer. Simply searching the web for something like "Windows update not completing" will show you what I mean.

Since it does complete, you should consider yourself lucky. Their suggestion, as you can see in your Windows update settings, is to set it to update automatically which would happen during the night while most people wouldn't notice it. There are drawbacks to it as you're probably aware, such as automatic restarts, but since you don't use the defaults, you have to live with your choices.

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