Why does Windows use backslash as path separator? (2019)

Original Article ↗ Hacker News Discussion ↗

Historical reasons for \ on DOS/Windows

  • DOS 2.0 adopted \ as directory separator because / was already used for command switches (e.g., FORMAT C: /S /U), influenced by earlier systems and IBM compatibility.
  • Article and commenters stress this was not directly from CP/M itself (whose core tools didn’t use / for switches) but from Microsoft’s own CP/M tools and DEC traditions.
  • Some dispute or are skeptical about exact lineage (CP/M vs VMS vs DEC), but the consensus is: DOS 2.0 + IBM constraints fixed \ early.

Forward slash actually works (mostly)

  • Many Win32 APIs and the OS core accept / as a path separator; you can often mix / and \.
  • Major exception: cmd.exe and some older tools, which interpret / as option prefix.
  • Newer shells like PowerShell handle / paths well and even accept Unix-like commands (ls, cd, etc.).

Long paths and \\?\ quirks

  • Historically MAX_PATH was 260 chars; NTFS itself allows ~32k chars.
  • Windows 10+ can remove this limit via registry/group policy, but some tools (Office, built-in zip, some Git clients) still misbehave on long paths.
  • Prefixing paths with \\?\ disables normalization: no /→\ conversion, no trimming of trailing spaces/dots, and enables long paths.

Cross‑platform and tooling pain

  • Many devs complain Windows paths complicate cross‑platform software (especially when joining URI-style / paths with Windows roots, handling UNC, escaping \ in strings).
  • Others argue the real issue is insufficient Windows testing and reliance on string-concatenated paths instead of path libraries (PathBuf, pathlib, C++ std::filesystem::path).

Backwards compatibility vs “fixing it”

  • One side: sticking with \ and line endings like CRLF is a legacy burden that should have been abstracted away in UI and tooling long ago.
  • Other side: backward compatibility (running old DOS/Windows apps unchanged) is core to Windows’ value; changing separators would break scripts, tools, and user expectations.
  • Some note that since Windows already accepts /, the main remaining annoyance is UI convention and shell quirks, not the kernel APIs.

Related issues: escaping and newlines

  • \ conflicts with escape syntax in many languages, requiring \\ in strings.
  • Debate over CRLF vs LF: some call CR unnecessary legacy; others note CRLF is standardized in Internet protocols and historically matched teletype behavior.