What is the essence of installing a Windows system?
What Is the Essence of Installing a Windows System?
Installing a Windows system involves complex steps, various methods, numerous tools, and ever-changing approaches. But no matter how much it changes, the core remains the same.
The essence of installing a Windows system boils down to two things:
- Extracting the WIM file
- Setting up the boot
Extracting the WIM File
All files required for installing a Windows system are stored in a single WIM file. We often call it the WIM package, because the essence of a WIM file is a compressed archive.
WIM archives have some unique features compared to other common archive formats. For example, they can preserve special NTFS file system attributes of compressed files, support chunked compression, store hash values of compressed files, and reference the same data block for identical files to reduce archive size.
The WIM package is a compressed file format invented by Microsoft. Microsoft also released a command-line tool called DISM (Deployment Imaging Service and Management) for editing WIM packages. However, since DISM is a pure command-line tool, it’s not user-friendly for those unfamiliar with the command line. As a result, many third-party tools with graphical user interfaces have been created by developers.
The essence of these third-party tools is that they all use DISM internally—they simply wrap a GUI around DISM and add some features that the developers personally liked.
So, no matter how much things change, the tools are all DISM, just with different “clothing.”
What Can DISM Do?
Here’s how Microsoft’s official documentation describes DISM.exe:
Deployment Image Servicing and Management (DISM.exe) is a command-line tool that can be used to prepare and service Windows images, including images for Windows PE, Windows Recovery Environment (Windows RE), and Windows Setup. DISM can be used to service Windows images (.wim) or virtual hard disks (.vhd or .vhdx).
DISM is built into Windows and can be used from the command line or from Windows PowerShell.
In plain English, DISM can edit WIM files, add or delete files from WIMs, mount WIMs to adjust their internal structure, package WIMs, compress WIMs, inspect WIMs, and much more.
To put it even more simply: any operation related to WIM files in the Dism++ software is essentially a DISM function.
Do I Have to Use DISM to Extract a WIM and Install Windows?
Not necessarily. Microsoft has publicly disclosed the compression and decompression algorithms for WIM packages. There is a third-party open-source software called wimlib that can also edit WIM files.
Unfortunately, wimlib is also a pure command-line tool, which can be a disaster for non-programmers.
Many third-party software tools can call upon either of these two WIM editing tools, so we have the freedom to choose. (For example, WinNTSetup.)
Can I Use a Regular Compression Tool to Extract a WIM to a Target Partition for Installation?
Using regular tools like 7-Zip or WinRAR, you can quickly open and view the files inside a WIM package, but you cannot properly extract them. The root cause is that WIM’s compression encoding method is not compatible with ordinary compression tools. WIM’s compression method is too complex and requires specialized decoding tools like DISM or wimlib.
Therefore, the first step in installing a Windows system is to use a specific decompression tool to extract the WIM package to the target system partition.
Setting Up the Boot
Installation tools (such as WinNTSetup, CGI, SGI, EIX, etc.) automatically set up the boot for us after extracting the WIM package. In fact, there is no direct connection between setting up the boot and extracting the WIM package to install the system. There is also no necessary relationship between the boot and the system itself.
A system without a boot is still a complete system—it just cannot start.
A boot without a corresponding system is still a valid boot—it just has no system to launch.
Setting up the boot means writing the boot files (EFI programs, BCD files, etc.) or boot code for the installed system into the EFI partition (ESP partition) on UEFI firmware computers, or into the MBR on BIOS systems. This is what UEFI or BIOS firmware reads to boot the system.
Without a boot, even if the system is complete, it cannot start.
Apart from extracting the WIM and setting up the boot, any other operations during Windows installation are likely just for system optimization and are not mandatory steps.
No matter which method we use to install Windows, the essence always comes down to these two steps, and the tools we call upon are largely the same.