Windows 95 installed a tiny Windows 3.1 first so you could answer setup questions sooner
Raymond Chen’s setup history explains a compromise that saved both engineering work and the person waiting to leave the keyboard for coffee.
Windows 95 could start its installation by installing a tiny Windows 3.1. The old operating system helped usher in the new operating system, then gave up the chair after doing the work needed to get the main installer running. Temporary Windows. Imagine that.
In Raymond Chen’s September 26, 2025 account, Setup had three programs. The first ran under MS-DOS and prepared the miniature Windows environment. A 16-bit Windows program did most of the installation work. A final 32-bit program ran inside the newly installed Windows 95 for the steps that required the completed operating system.
Starting from an existing Windows environment could enter the process at the second part. The DOS path needed enough graphical infrastructure to run that same main installer. A miniature Windows 3.1 was already available and debugged, so the team could reuse it while Windows 95 itself was still under development.
The miniature environment was small enough to make the choice tangible. Chen gives MINI.CAB on Setup Disk 1 as 441,905 bytes, expanding to 815,307 bytes. Those numbers belong to this cabinet and its extracted contents. They describe the little environment needed for this stage, with no claim about the size of an ordinary Windows 3.1 installation.
A reader had asked why Microsoft did not use a miniature Windows 95 instead, making the main installer a 32-bit program. Chen explains that somebody would first have had to build that variant, then keep it working as Windows 95 changed. A late project would acquire another little operating system to maintain (sure, squeeze it in).
The replacement design also added work before the user could answer questions. Chen sketches an extra copy stage and a reboot into miniature Windows 95, followed by another reboot into the final installation. A larger temporary environment could require another floppy swap before the main interaction even began.
For the person at the keyboard, that distinction is practical. Answering the questions early lets you walk away while the machine continues. An initial copy, disk change, BIOS startup and temporary boot keep summoning you back before you get the chance. The machine can spend its own time copying files; making a person sit through that work before answering the questions is an additional cost.
Chen calls the intended constraint the “only one reboot” principle. His explanation of the alternative is a design comparison, including estimated sizes for a hypothetical miniature Windows 95. Those estimates should stay hypothetical; they are not evidence that Microsoft shipped a second installer with those exact disk requirements.
The same article considers adding Win32s and explains why it would bring its own reboot and extra components. Each attempt to make the middle stage newer added work the temporary system would perform once and discard. Windows 3.1 was already waiting on the shelf, ready to get Setup far enough along for the customer to leave.
Coffee before another reboot.