How long does the 1903 upgrade take using Windows Update?

Short answer - a very long time.

I had reason to take my System One below back to an earlier system image and upgrade it to 1903 again. In fact, the image I restored for this machine was its 1511 image from mid-2016. I then upgraded this to 1809 using an ISO in about two hours.

Just for fun (?) I decided to let Windows Update perform the Feature Update to version 1903. Now this machine had previously been updated from 1809 to 1903 using an ISO, so I knew that method took no more than a couple of hours. How much longer could Windows Update take?

Well, it would be expected to to take a little longer, because it uses the Unified Update Platform (UUP). This is designed to reduce the download size of an update by only downloading the changes, not the full set of files as are used in the ISO.

Microsoft said:

...one of the biggest benefits UUP brings to our customers is a reduction in download size of build updates on PCs.... Differential download packages rely on re-using files on your current OS to reconstruct the newer OS. This could include copying files as-is that have not changed between builds, or it could involve applying “binary deltas”� or “diffs”� to old files to generate newer files. Differential download packages are smaller and can take a shorter amount of time to download.

For a full build, we refer to this as a canonical download package... Canonical download packages tend to be larger in size and may take longer to download.

..as we roll out UUP in our retail release, users can expect their download size to decrease by approximately 35% when going from one major update of Windows to another. For retail users, the first time they get the UUP client code is part of the Creators Update, therefore, they will see the benefit of differential download packages when they go from the Creators Update to the next feature update of Windows.

An update on Unified Update Platform (UUP) for Windows 10


So, the download is smaller, but there's more work to do with it after downloading. I told Window Update to 'Download and install now', set the stopwatch going and opened Task Manager to watch what was going on.

The first step was Windows Update saying "Getting ready". This stage took 15 minutes to complete, then the download began.

Windows Update said "Downloading - 0%" which climbed steadily to 99% while Task Manager showed steady download progress. Network activity virtually ceased after 3.5GB had been downloaded in 15 minutes (this time is entirely dependent on your broadband speed).

The step from "Downloading - 99%" to "Downloading - 100%" took an astonishing 42 minutes, during which there was little or no network activity but a lot of CPU activity, mostly from the Windows Installer. This would presumably be the "applying “binary deltas”� or “diffs”� to old files to generate newer files" stage.

Then Windows Update first said "Pending install" then quickly switched to "Installing - 0%"....


....Paint would have dried quicker - it took a further three hours and ten minutes to get to "Installing - 100%" and asking me to select a restart time to complete the install.

Then, on the restart, it rejoined the same steps of 'installing updates' and restarts that an ISO upgrade would have followed, taking a further 40 minutes.


So, in conclusion what would take less than two hours with an ISO (I know, because I have previously used the 1903 ISO on this machine) took over four and a half hours via Window Update. I can't say I'm that impressed. At least it worked reliably, I'll give it that. And I suppose I could have continued using the machine while the update ground away in the background (I didn't though, I went out for an hour or so instead). At least I now sport a nice entry in the Update History.....

Ztruker said:

The really sad part is this is what most users are going to see....

Well, until this new 'Download and install now' function was added many users didn't even realise anything was going on until they saw the notice to restart and complete the install. They were blissfully unaware of just how long it was taking in the background. Now of course they will know exactly when the update started because they have to ask it to start.

@Bree > the Windows update windows auto closed after staying in status: Downloading 100% for over an hour...is that how it is?
Do I open the windows update via Settings again?

onlytanmoy said:

... the Windows update windows auto closed after staying in status: Downloading 100% for over an hour...is that how it is?

No, it did not close from me.

Do I open the windows update via Settings again?

Yes, if all is well it should now say 'pending install' or 'installing'. It may say 'downloading' again if that stage hadn't completed. If it doesn't say anything, try checking for updates.

@Bree thanks for your response mate.
I opened the Win update via settings and this time it says Status: Installing - 53% ,phew

onlytanmoy said:

I opened the Win update via settings and this time it says Status: Installing - 53% ,phew

Good, looks like it is on course. This stage can be slow, so have patience.