I have Windows 7 PCs that have automatic update turned off. I do updates in batch once a month or so. But each time "check for update" takes 15 to 30 minutes. I don't understand why checking for updates can be so slow? I have to wonder what is happening in the background. Is it computing hash? Are my PCs with automatic updates enabled suffer the same fate every time it boots up (only that I wasn't aware)?

  • 1
    It seems like background application are running. How did your system performance?
    – BDRSuite
    Mar 16, 2015 at 8:08
  • 1
    My PC performs fine. CPU hardly went over 10%. I didn't notice anything unusual while it is "searching for updates".
    – some user
    Mar 17, 2015 at 23:11
  • Why are you disabling Windows Update in the first place? It could run in the background and you wouldn't even notice until it asks you to reboot, which you don't have to do immediately.
    – gronostaj
    Jun 26, 2015 at 18:36
  • 3
    I like to update in batch so I can rollback if something went wrong. Background updates are hard to track and time consuming to rollback. And with manual update, I also have the option to review the changes before proceed. Also, once in a while I help people to clean install their PC and I am faced with the same problem.
    – some user
    Jun 26, 2015 at 20:48
  • 5
    @someuser You can have the best of both worlds: Configure WU to Download updates but let me choose whether to install them which will scan for required updates in the background but never install them without your approval. They won't auto-install but all applicatble updates will be listed when you do your monthly patching routine. Jul 1, 2015 at 18:40

11 Answers 11


The checking for updates part is so slow because:

  • Windows 7 uses Component-Based Servicing, which means Windows Update has to work ridiculously hard to determine file and component dependencies/inter-dependencies, maintain side-by-side versions of older files/components, while still making it possible to uninstall individual updates/components but without breaking any other updates/components, all the while taking into account supercedence and god knows what else. The code that does all this must be hellishly complex.

  • Windows 7 64-bit has to maintain both 32-bit and 64-bit versions of each update.

  • Windows has to maintain both GDR and LDR versions of each update, which means on Windows 7 64-bit you get 32-bit GDR, 32-bit LDR, 64-bit GDR, 64-bit LDR for each update.

  • The code behind Windows Update is highly inefficient, probably due to its conceptual complexity. My observations over the last few years are that, as the total number of released updates has increased, update check time has increased in an almost exponential way. To me that's indicative of some kind of recursive algorithms being employed, perhaps to determine superscedence or resolve dependencies.

Unfortunately for us, Microsoft don't like talking about Windows internals so we end up having to figure it out for ourselves or speculate.

  • 3
    This also seems to explain why installing updates is so slow. Is there anything that can be done about it? Jul 2, 2015 at 4:45
  • 3
    @MichaelHampton In my experience, three things can help: 1 Get a PC with excellent single-threaded performance and large CPU cache (e.g. 3.4 GHz i5/i7 Haswell), 2 Get a SSD hard drive, 3 Disable the real-time monitoring component of your AntiVirus software while installing updates.
    – misha256
    Jul 2, 2015 at 5:04
  • 6
    @MichaelHampton Some folks have given you mis-information. The MS Update Servers are generally very fast. And scanning your PC/HDD for things to update is also, usually, quite fast. When you next do an update check, open up Resource Monitor first so you can see for yourself what parts of the update take up so much time. You will find that, initially, some time is spent thrashing the hard drive and talking to the internet. After that's done, you will see one CPU core sitting at 100% for an eternity. That's the update engine on your PC figuring out (inefficiently) what to do next.
    – misha256
    Jul 2, 2015 at 5:39
  • 3
    @someuser Yup, indeed. But you're looking at overall CPU utilization. Look at the CPU utilization of single cores. During Windows Update, you'll see one core maxing out at 100% for eternity. Windows Update engine is clearly CPU-bound to a single thread. Sure RAM usage is high too, but that's not the cause of the slowness. It's the update engine's algorithm that's complex and/or inefficient.
    – misha256
    Jul 2, 2015 at 21:44
  • 6
    How come Debian does all of that, and only takes between a few seconds, and 5 minutes (if it is a very big update). With little CPU usage, it does it quietly in the background, you can shut-down part way through, and you rarely have to reboot. Mar 11, 2017 at 16:46

Several facets of the problem were treated in the existing answers. I will try to tie them together by listing the causes in a general manner, without repeating what has already been said:

  1. Microsoft Windows Update mechanism is extremely sophisticated, which unfortunately also means complicated
  2. WU needs to support an incalculable number of hardware and software combinations
  3. WU needs to apply the updates in the correct order
  4. Windows 7 is an older system, and SP2 is overdue and will probably never arrive, which makes for very many updates
  5. The last years, Microsoft was under a great pressure to fix numerous security problems, which resulted in very many hectic fixes, then fixes of fixes and so on to the n'th generation
  6. Microsoft has not been able to optimize enough the update mechanism, which is in general an exponential algorithm, resulting in a brute-force algorithm which is rather slow.
  7. Microsoft's WU servers are sometimes over-burdened.

Let us look at these points more in detail.

Windows Update complexities

After an update is released, it can enter into three additional different phases over time: Revisions, Supersedence, and Expiration.

Update Revisions: When changes are made to a previously released update, it's called an Update Revision, where some pieces of the download are changed. This is a partial, not full, update replacement.

Superseded Updates: This is a complete replacement of a previous release, or releases. Sometimes Microsoft will wrap multiple releases into a single package, and that package replaces its encapsulated updates.

Expired Updates: These are updates removed from the list of valid updates. Such updates are no longer applicable and will not be detected for installation. Most times, an update is expired after it is replaced by a Superseded Update.

Updates have also a dependency mechanism, which means that some updates may require other updates to be applied first.

Expired Updates are problematic to WU performance, since unfortunately they are not removed from the computer, so they still take part in the calculations, and there are so many of them. Some improvement may be achieved by using Disk Cleanup to Remove Outdated Windows Updates (take first a backup disk image of the system drive, since WU is also very fragile).

WU Calculations

Because of the enormous number of possible combinations, Microsoft keeps all updates on the WU servers in the format of a humongous tree. Deciding on which updates need to be applied is done by a tree-pruning algorithm, which takes into account the client's installed hardware and software, as well as all the updates that are already installed, which is by itself a large body of facts that need all be applied successfully when pruning.

The algorithm is not guaranteed to succeed, meaning that WU is perfectly capable of destroying the OS or even rendering it unbootable. This is entirely understandable, for example taking an update A1, having revision A2, where an update B depending on A was released between A1 and A2. Now go figure whether the order of installation should be A1-B-A2 or A1-A2-B, when the wrong decision can be deadly.

Overburdened WU servers

Wikipedia has this to say about Windows Update statistics :

As of 2008, Windows Update had about 500 million clients, processed about 350 million unique scans per day, and maintained an average of 1.5 million simultaneous connections to client machines. On Patch Tuesday, the day Microsoft typically releases new software updates, outbound traffic could exceed 500 gigabits per second.

These numbers have probably doubled by now, and explain why the WU servers are sometimes unreachable. I am using the WU option of "Check for updates but let me choose", and my own experience is that there are days and times when checking for updates takes longer than I'm willing to wait, requiring postponement.

The long history of Windows 7

Windows 7 was released on July 22, 2009. After about 17 months, Service Pack 1 (SP1) came out on February 22, 2011. This was about 4.5 years ago, which means that SP2 is long overdue.

The good side of a Service Pack is that installing it wipes out the entire update history, so that in effect WU starts from zero, exactly as after a fresh installation of Windows. This of course speeds up enormously all the calculations, since there are fewer updates to take into account.

The sheer number of existing updates since SP1 explains why WU calculations are so slow today. For Microsoft the problem can be solved "simply" by upgrading to the more recent Windows 8.1 or Windows 10, so WU will have a smaller number of updates to take into account.


As Microsoft still continues to apply numerous updates to Windows 7, WU will only keep on slowing down as time passes.

One possible optimization is to Remove Outdated Windows Updates. Another is to use the WU option of "Check for updates but let me choose", and check for updates early morning or late at night.

Most updates also apply to Windows 8 and 10, so the burden on Microsoft's WU servers will only multiply when Windows 10 is soon released. Microsoft also seems to parcel the bandwidth of its WU servers according to its own policies, with the accent on serving the more recent operating systems, so we should expect another slow-down for Windows 7 once Windows 10 is released, together with disproportionately faster updates for Windows 10.

If WU is too slow, the only real solution is to upgrade to a later version of Windows.

Good news : SP2 for Windows 7 (and 8.1) has arrived

Microsoft has published what is actually SP2 for Windows 7 and 8.1. This update will not be available from Windows Update for some unknown reason, so has to be manually downloaded and installed.

Read about how to get it in the article :
Microsoft overhauls Windows 7 and 8.1 updating -- but don't call it a service pack.

  • 2
    Checking for updates in Windows 10 preview has been very fast. Jul 4, 2015 at 16:16
  • I have a feeling that checking for update is still a CPU and memory intensive operation. But maybe the program is written such that it yields CPU from time to time and therefore not slowing the PC down. I have to wonder if for those who have automatic update turned on, does the computation happens every time the PC is turned on?
    – some user
    Jul 6, 2015 at 16:11
  • The answer by @Renju claims the existence of a cache, but in my experience checking for updates is equally slow even if done immediately after a previous check. My own uninformed opinion is that the pruning is done on both the WU servers and the client. I would guess that on the server by hardware and installed Microsoft products/OS; on the client by the updates that are currently already installed on the computer.
    – harrymc
    Jul 6, 2015 at 16:43
  • 2
    This guess is motivated by the poster's remark about WU using a lot of RAM but not enormous amount of CPU. This is consistent with a large tree of updates downloaded from Microsoft into local memory, and perhaps a local pruning operation that requires still more info from Microsoft.
    – harrymc
    Jul 7, 2015 at 15:50
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    "The algorithm is not guaranteed to succeed, meaning that WU is perfectly capable of destroying the OS or even rendering it unbootable. This is entirely understandable" What a load of nonsense. Dec 9, 2015 at 12:20

This issue has come and gone over the years with different fixes along the way, so here is my updated guide to this issue as of this date January 5th, 2016

Check the EDIT section below, there is a much faster way to fully update Windows 7 SP1 after a clean install as of May 2016.

This is what I do when I reinstall W7 with SP1 or have issues with Windows update stuck on checking for updates.

If Service Pack 1 is not installed, install it before following this guide.

Download KB-3138612 and save it where you can find it later

Download SUR Tool save it to same place

Restart the PC and disconnect from internet before Windows loads, this is important because at every boot windows will check for updates in the background and this will start the checking for updates hang all over again and will prevent the install of the downloaded packages until it finishes checking, so disconnecting from the internet before Windows loads prevents this.

Once booted install KB-3138612, if reboot is required do so and stay disconnected from internet.

Now install the SUR Tool package, this is a big package and will install many updates along with cleaning up and repairing the Windows update store. It will also cut down on how many more Windows updates will need to be installed later.

After install of SUR package reboot, connect to internet and do a manual Windows Update, it should work much faster now. Even after these fixes I have seen some W7 PC's take up to an hour to finish checking for updates if launched from Control Panel manually.

If you have other Windows updates issues and the 2 updates above are installed, download this Microsoft Windows Update fixit tool (right click "save link as") run it and select aggressive mode to completely reset Windows updates. Reboot and try Windows Updates from the Control Panel again. This tool fixes issues when the other Microsoft fixit tools fail, at least in my experience.

Update: Microsoft has released a huge update rollup for Windows 7 SP1, this is similar to a service pack but they are not calling it that. This will make it Much faster to update Windows 7 after a clean install, no more Windows update issues and many reboots. This update rollup will bring the system current to patch Tuesday of April 2016.

This is not being released through Windows Update, you have to use Internet Explorer to get it, open IE and go to this address


Type in the search box 3125574 and hit enter key.

enter image description here

Now you will see all versions of this rollup, select the one you need and download it somewhere you can find it later.

enter image description here

Also use the Windows Update Catalog page to download and install this update first, 3020369, it is a pre-requisite for the rollup, then install 3125574, also be sure to be disconnected from the internet when applying these updates.

  • Great info thanks. I'm currently struggling with getting a low-spec laptop up to date from a fresh install of W7, so I'll be giving your process a shot tonight. Have you ever noticed, after installing the SP1 redist, that WU still then wants to download and install all the pre-SP1 updates, as well as SP1 itself? And if so do you have any idea how to avoid it? I've seen this quite frequently of late, and I assume that I've just done something in the wrong order. (I usually go Install W7 > Install chipset/gfx drivers > install SP1 redist > check for updates.)
    – blackworx
    Mar 22, 2016 at 6:32
  • 1
    I have seen that behavior, I just let it download and install again, usually when the kb installer runs it sees they are already installed and moves to the next update in the chain, basically it skips those that are already installed. The SUR tool should solve this issue.
    – Moab
    Mar 22, 2016 at 17:32
  • 1
    This worked for me after installing KB-3138612 offline (download it, cut internet connection, install). I then rebooted and MS update was prompting to download packages within a few minutes.
    – AndyC
    May 13, 2016 at 10:36

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 June 2016, which is part of the Windows 7 July 2016 Update Rollup, the update search is fast again.

  1. Download:

Takes only a bit over 1 minute for me to search for new updates. To speedup the setup up of the update KB3172605, stop the WindowsUpdate service (net stop wuauserv).

This WU service stop trick speeds up install a lot, when you install several MSU updates:

FOR /R "%~dp0" %%A IN (*Windows6.1-KB*.MSU) DO (
        CALL :SUB %%~nA        
    ECHO= Installing KB!KB_NUM!        
    >NUL net stop wuauserv
    WUSA "%%A" /quiet /norestart)
ECHO= == Press any key to close the Window ==



FOR /F "DELIMS=-" %%B IN ("%KB_NUM:*-KB=%") DO SET "KB_NUM=%%B"

In Windows 10 Microsoft fixed the issue by following my suggestion and make the updates cumulative. Here you only need 1 large update to be at the current patch level. This slow checking is no longer needed.

  • 1
    Seems KB3138612 fixes it on most W7sp1 fresh installs, but I did one yesterday and it still took over an hour to give a list of updates, also I notice on most of my W7 PC's when it starts downloading the updates the screen does not refresh and stays at 0% downloaded until all are downloaded and starts to install them, Windows Update is still broken.
    – Moab
    Apr 24, 2016 at 16:54

If past experiences with the XP update are any indication, they occasionally let slip an exponential-time algorithm in there. Which once you have many updates... takes forever. Currently the Win 7 updates are in a similar situation; take a long time, although there's no official explanation for this latest bout of slowness yet. It's interesting that this "just happens" (to the old versions) when they have a new one out. The cynical me can't help but imagine that someone might intentionally want that to happen, along the lines of [old] Windows is slow? You need a new version. Or maybe it's just the MS way of starting the holiday season.

There is a hotfix for some kind of WU slowness, which is not being offered automatically (i.e. via update itself): https://support.microsoft.com/en-us/kb/3102810 Alas it did not make a real difference in my case, and I've tried it on two different computers one 32-bit and one 64-bit. Also it has been around since October, so it's probably not for the latest issue[s].


There are about a billion PCs running Windows today. Each PC has some combination of hardware, accessories, OS version, language, IE, device driver version, Microsoft software at various patch levels, security updates, etc. The Windows Update system has to sort through all these combinations to offer the right updates for an individual PC. Each update has properties including dependencies and a "supercedence" structure.

The first step (first run) in the scan is to determine the OS version, SP, language, PC manufacturer to prune the tree of likely updates for the PC. Based on that first scan, a likely set of update IDs are sent to the device and the local client computes which updates are installed, superseded, etc. and then sends that list to the server and also caches a copy locally for subsequent scans. The server responds to the client request for updates with descriptions, etc. that are displayed in the UI (in the appropriate UI language).

Once a day, a check update is done by the Automatic Updates client in the background and refreshes the local cache of installed updates, so that subsequent scans are just a delta and fast. These are stored in the %windir%\softwaredistribution folder on the PC.

A similar process is also performed for previously downloaded updates. The service won't re-download the packages.

Found this post which will help us to at least understand what's really happening during searching. It is written beautifully. So I am posting it as such. You may find the original post at here

A noticeable change in time taken for checking update for installation was there when I changed the Windows update settings to Check for updates but let me choose whether to download and install them

  • "The Windows Update system has to sort through all these combinations to offer the right updates for an individual PC." Yeah, that sounds like a SELECT operation all right. If only there were algorithms to quickly search in large tables, one could call them "indexing". That would help. Feb 1, 2016 at 17:17

Your best bet in my opinion is to just enable windows updates and switch to the option which lets you download updates but not install automatically. That way, you can get what you want installed without having to wait for checks or background file downloads.

Now, to answer why it's slow. I think it simply comes down to the fact that windows updates was built with the reduction of noticeable impact to users in mind. It uses the BITS service (background intelligent transfer service) to check for and download updates.

Again, the focus with this service is to work in a way that's not disruptive to the user. Speeds are intentionally slow by design as Microsoft never intended clients to turn the update service on and off every month.

What you might look into is getting your own WSUS server setup. That way you can deny updates much the same way enterprise admins do and it can apply or deny those chosen updates to all of your windows devices you own. Making that chore of selectively updating, less of a chore.

  • 1
    Now that's a thought: that it's intentionally slow. This does make it a real pain to update right after a reinstall, though, which is the situation I'm in now. Some way to speed this up (without setting up a very large WSUS server) would be useful, if possible; waiting a couple of days before being able to use the computer would not be nice... Jul 1, 2015 at 18:48
  • What about just leaving the updates on but setting it to (just download. Don't install automatically)? That way, you can pick and choose what's available and it won't install anything unless you approve of it first. That option seems to solve all of your criteria.
    – Geruta
    Jul 1, 2015 at 19:01
  • Right, but I still have to wait for it. And wait and wait and wait and wait... Jul 1, 2015 at 19:03
  • If you are having it check for updates at 3am and you leave your PC on all the time, it will check and download when you are asleep. Making it fully available and ready for you to play with when you wake up.
    – Geruta
    Jul 1, 2015 at 19:04
  • 1
    There are third party tools to download windows update and a MBSA scan is pretty fast and will give you a list of all missing updates. There was also recently a Windows Update patch (KB3050265) for Windows 7 since Microsoft recognized how agonizing (and non-performant) their implementation was for machines with smaller amounts of RAM. Jul 1, 2015 at 19:29

It is slow because Windows Update and several other Windows system components use the Microsoft JET Blue database engine, which suffers from notoriously bad performance and is an overall resource hog.

Like others have mentioned, there also appears to be some degree of recursion in the Windows Update code itself, leading to poor performance as the number of updates increased.


Just to add another data point. I recently have to bring up a Vista PC. I manually upgraded Vista from SP1 to SP2 but checking for update takes forever. Nothing happened for 24+ hours.

I did some googling that found a solution which includes installing the following updates:

http://www.catalog.update.microsoft.com/Search.aspx?q=KB3205638%20vista http://www.catalog.update.microsoft.com/Search.aspx?q=KB4012583%20vista http://www.catalog.update.microsoft.com/Search.aspx?q=KB4015195%20vista http://www.catalog.update.microsoft.com/Search.aspx?q=KB4015380%20vista

After downloading and installing the updates manually. I ran update check for 10 min and it found 200 updates. Keep in mind this is for Vista but I think maybe something similar exist for Windows 7 too.


I had this problem and what I did was let Windows Update run overnight for the first time on a freshly installed machine. Tips to successfully do that:

  • Go to the energy options, set the standby time to "never"

  • Turn automatic Windows Update on. The default time of 03:00AM is ok since the search process also takes time

  • It is also recommended to do a "Windows update needs to update some components ..." process the first time (goes quickly compared to the more than 200 updates in case of Windows 7)

When everything has been updated correctly, you will find a huge amount of patches (about 200) were installed. Windows also defragged and ran Windows Defender updates/scans as well.

After that, the remaining Windows Update cycles (search for updates - install - reboot - search for updates - install - reboot - search for updates ... until # updates has become 0) work much faster.


Not hashing, but yes, it's checking a lot (as deep as some DLLs file version). It is slow no matter what system you use.

As a solution, keep it off and when there's a day or night you don't need the system too much, turn it on, force it to check for updates and let them all install.

  • 4
    Do not recommend turning off Windows Update. When a zero-day vulnerability is found, Microsoft rolls out a critical update immediately when it's available, out of their normal schedule. Computers with Windows Update disabled won't receive it and will be left vulnerable, while other computers are being patched, so probability of getting attacked spikes upward.
    – gronostaj
    Jun 26, 2015 at 18:33
  • Statistically, the updates create way too much anomalies to justify a vulnerability prevention in this manner. If a ZDV is found, that specific critical update can be installed without affecting anything else.
    – Overmind
    Jun 30, 2015 at 11:35

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