Operating systems manage filenames differently due to fundamental filesystem rules. macOS (using HFS+ or APFS) typically treats filenames as case-insensitive, meaning it doesn't distinguish between uppercase and lowercase letters (e.g., "File.txt" and "file.txt" are considered the same name). Windows (using NTFS or FAT32) defaults to case-insensitivity but is case-preserving, so while "Document.doc" and "document.doc" are treated as identical, the system remembers the exact casing used when the file was named or last saved. Windows also reserves certain characters like \ / : * ? " < > | , which macOS generally allows (though using them can cause issues when transferring files).

For example, saving a file as "Project.docx" on a Mac and later attempting to save another version as "project.docx" in the same folder will trigger an overwrite warning on the Mac but not necessarily on Windows if the casing differs slightly. Similarly, copying a folder from a Mac containing "readme.TXT" and "README.txt" to a Windows PC might result in Windows treating them as the same file and replacing one, causing data loss. Adobe Photoshop files shared between platforms often encounter renaming quirks when collaborators use inconsistent capitalization.

These inconsistencies primarily arise to maintain backward compatibility and manage technical constraints. They can cause significant issues during cross-platform file sharing or collaboration, especially for developers or designers. While macOS's approach simplifies local file management for users, it creates ambiguity when working with Windows systems or Unix-derived tools expecting case-sensitivity. Users must be mindful of casing conventions and avoid problematic characters when sharing files across OS environments to prevent unintended overwrites or errors.