Why did Windows 95 setup use three operating systems?

Original Article ↗ Hacker News Discussion ↗

Windows 95’s installer famously relied on three layers—MS‑DOS, a stripped‑down Windows 3.1, and finally Windows 95 itself—highlighting how tightly early consumer versions of Windows were coupled to DOS and 16‑bit infrastructure. Commenters use this as a springboard to unpack how Windows 3.1 functioned as “almost an OS,” how protected mode, virtual 8086 mode, and bundled “runtime” Windows versions enabled gradual transitions in drivers and applications, and how similar ideas live on today in WinPE for modern installers. The conversation also contrasts Microsoft’s emphasis on backward compatibility with the more brittle ecosystems of Linux and macOS, and reflects on changing UI quality and system robustness from Windows 95 through NT, XP, and Windows 10/11.

Windows 3.1, DOS, and Windows 95 Architecture

  • Debate over whether Windows 3.1 was “just a shell” on DOS:
    • One view: primarily a GUI shell with DOS handling drivers, disk I/O, and config (config.sys, autoexec.bat).
    • Counterview: functionally “95% of an OS,” managing memory, processes, input, graphics, and many drivers while DOS mainly provided filesystem and legacy app support.
  • Discussion of 386 protected mode, v86 mode, and virtualized DOS/BIOS:
    • Windows for Workgroups 3.11 and Windows 95 use DOS as a bootloader, then switch to protected mode and run DOS in a VM, trapping BIOS and some I/O.
    • Over time, more drivers moved from DOS/BIOS into 32‑bit VxDs, culminating in 9x being able to run without leaving protected mode for most operations.

Runtime Windows and Why Setup Used Windows 3.x

  • Historical “runtime” Windows shipped with apps like Excel, PageMaker, Word, and some scanners:
    • Stripped‑down Windows 1.x/2.x/3.x with no general shell, intended to run a single app (or a very small set).
    • Still required DOS; early Windows used DOS for all file access.
  • Windows 95 setup reused the same idea: a minimal Windows 3.x environment to host a 16‑bit installer, rather than inventing a tiny “Windows 95” just for setup.
    • Suggestion to have a “bare 95” that the installer could reboot into is dismissed as extra complexity and disk space for only cosmetic gains.

Modern Windows Setup (WinPE and Relatives)

  • Current installers boot into Windows PE, a stripped‑down NT environment used for installation and recovery.
    • It uses the same kernel generation as the target OS, though the UI assets largely date back to Vista.
    • WinPE is distinct from Windows CE and from embedded NT variants used in ATMs/signage.
    • Installing and injecting drivers into WinPE is described as quirky and more limited than full Windows.

Backward Compatibility and DOS/NT

  • NT 3.51’s stricter DOS compatibility prompted user backlash; 16‑bit apps and DOS behavior lingered far longer than designers expected.
  • Comparisons with Unix/Linux and Solaris:
    • Some Unix systems (e.g., Solaris) are praised for strong binary compatibility.
    • Linux compatibility depends heavily on userland libraries; containers are seen as a modern workaround.
  • Windows’ long‑term ability to run decades‑old software is cited as a key reason for its desktop dominance, though it adds complexity.

Upgrade Chains and Multiboot Experiments

  • Discussion of whether an install can be upgraded from very old versions (DOS/Win95) all the way to modern Windows without reformatting.
    • Some describe elaborate multiboot setups: DOS and Win9x on FAT32, then XP on FAT32, then NT‑based systems (7, 10, possibly 11) on additional NTFS partitions, all chained via boot loaders.
    • YouTube experiments are referenced showing very long upgrade chains.

UI/UX, Stability, and Performance Opinions

  • Mixed views on Windows 95:
    • Some recall it as unstable and crash‑prone compared to today; others remember it as usable and revolutionary for its time.
    • Windows ME is generally regarded as worse.
  • Comparisons with classic Mac OS:
    • Mac is praised for always‑graphical, polished boot and install flows, and simple system installation (copying a System Folder).
    • PCs’ text‑mode BIOS and flickering mode switches are attributed to heterogeneous hardware and legacy constraints.
  • Modern Windows UI:
    • Some praise current Windows 10/11 UI as solid and continually tweaked.
    • Others see regression: removal of features (e.g., vertical taskbar), ads in the Start menu, right‑click changes, animation slowdowns, and reliance on continuous, incremental changes.
    • Running old XP in a VM feels snappier to some, highlighting perceived bloat and overhead (registry chatter, UI animations, security/ACL checks, and poor small‑file performance vs Linux).

Market Inertia and Lost Diversity

  • Nostalgia for the 80s–90s era of many competing platforms (Commodore, Atari, Acorn, etc.).
  • Microsoft’s OEM contracts, strong backward compatibility, and the IBM PC standard are cited as locking in the platform and making new mainstream OS+hardware entrants rare.

Reflections on Chen’s Material

  • The broader blog (beyond the linked post) is valued for:
    • Explaining internal design trade‑offs (e.g., “what if two programs tried this?” as a mental model for rejecting certain APIs).
    • Illuminating how Windows balanced compatibility, UX, and architecture through the DOS–9x–NT transition.