Question Is it possible to pre-decompress compressed Windows installation files?

May 21, 2021
Windows installation media contain large compressed files like the 400MB boot.wim and 3.6GB install.esd files in Windows 10 and similar ones in earlier Windows versions. I assume that these are decompressed on the fly during installation. Is it possible to save these files in uncompressed condition to speed up the installation? If so, how does one go about making the installer recognize them?

Of course, decompressing these files and copying the smaller components to a flash drive will take some time, but it will be worth it (at least to some people) if the installation is done more than once. Inexpensive modern USB flash drives have ample space for these files in uncompressed form.


If you work with an SSD and a good quality pen drive, coupled together with a USB 3.0 port, the time for installing/reinstalling the OS shouldn't take more than 10~15 minutes(leaving out any driver installs if tethered to the www). FYI, decompressing the files and then tampering with the installer will only create grounds for a corrupt installer, best leave it as is.
May 21, 2021
Agreed that a normal installation doesn't take long. I timed my last Win10 21H1 installation and it was a hair over 10 mins on an entry-level computer. But this is partly of academic interest and probably a practical one for some. After all, the most often cited result of replacing an HDD with an SSD is perhaps the fact that it reduces boot-up time by what? maybe half a minute? In any case, I was hoping that there'd be a simpler way than hacking the installer.
wim are windows image files
You can use imagex to transfer the instalation.wim from a installation usb/dvd to a hdd/sdd so that the installation will be done on the target system without any decompressing.
All you need is imagex you can download gigabytes of stuff from MS to get it, or you can search for imagex alone on the web.
The only command needed is this one.
(Of course you'll have to make sure that the drive has an active and bootable partition)
imagex /apply N:\Images\my-windows-partition.wim 1 W:\

All you have to do is change the drive letters, if your dvd or mounted iso is D:
and the target hdd/ssd is E:
you use
imagex /apply D:\sources\install.wim 1 E:
the 1 at the end tells it wich list item to use.

Make triple sure that you use the proper drive letter for the target, all data on that disk will be destroyed.

If you have a dvd with multiple versions you can use
dism /Get-WimInfo /WimFile:F:\x86\sources\install.esd /index:1(2-3... )
to see which is which.
Make a folder with all the drivers on the disk so they will be available to windows after its booted up and your done.

As stated first make sure to make the drive primary and active so that it will start up when you put it into the other system.

.esd is a different format and you would have to convert it to .wim first.