Longtime Microsoft software engineer Raymond Chen recently answered an interesting retro tech question from a game developer on X. The developer asked why three different user interfaces were used in the design of the Windows installation options 95: DOS, Windows 3.x, and Win9x?
Chen, who has more than 30 years of experience influencing Windows development, answered this question on The Old New Thing website. He said that the answer to this question is much more complicated than it seems. -everyone thinks.
He said that at that time Microsoft expected that the Windows 95 installation program could start in three different environments: MS-DOS, Windows 3.1 and Windows 95, so it was decided that it must be compatible with three different system environments. .
One option to solve this problem is to write three separate Windows 95 installers: one to install from MS-DOS, another to install from Windows 3.1, and a third to install from Windows 95 to install.
However, this is not a satisfactory option because you are basically doing the same task three times and then using it in three different environments, so the code you write will probably be three times longer. much.
Therefore, they felt that a better option was to write an installer for only one version (Windows 95) and use it for all three starting points.
| from | Type of application | ||
|---|---|---|---|
| operating system | 16-bit graphical user interface | 32-bit graphical user interface | |
Therefore, if a Windows 95 installation program is written as an MS-DOS application, this DOS application can run on all three platforms due to backward compatibility. You just need to write an installation program.
However, this solution has a big problem, that is, it is a text mode installation program, which looks ugly. For a new Windows operating system platform, seeing such an ugly interface when you first install it is unlikely to leave a good impression on people.
So, the other extreme is that a Windows 95 installation program can be written as a 32-bit GUI program, but this means that if the user boots from MS-DOS or Windows 3.1, he must “Windows 95 a install first” before it can. execute this Windows 95 installation program, which seems to be stuck in an infinite loop.
Then there’s a compromise: Let the MS-DOS installer install a minimum version of Windows 3.1, just enough to support the functionality required by the 16-bit GUI installer. When you’re done, launch the small version of Windows 3.1 and run the 16-bit GUI installer.
Ok, now we have the three parts of the installer (check the picture below).
If you are installing from MS-DOS, use the first one: it installs a small version of Windows 3.1, then boots to Windows 3.1 to proceed to the next step.
The second part of the installer runs as a 16-bit Windows application, which can be a small copy of Windows 3.1 (if the user is upgrading from MS-DOS), an actual copy of Windows 3.1 (if the user is upgrading from Windows 3.1), or a genuine copy of Windows 95 (if the user is upgrading from Windows 95). The second installer does almost all the real work: it does the initial interaction with the user, gathers information about how to install Windows 95, how to ‘ asks which optional components to include, and detects hardware to decide which drivers² Then it creates drivers and Windows 95 files are copied to the system, old situations transfer to the new operating system, and send them to Windows 95.
The third part of the installer works as a 32-bit Windows application. It runs on a real Windows 95 system and performs some of the final steps needed to run a live system, such as installing a printer.
This is why the Windows 95 installation is actually three installers packaged together, allowing one copy of the code to be used for all three installation scenarios.
source:devblogs.microsoft.com/oldnewthing
