Object File System

Object File System (OFS) is an installable file system included with Microsoft Cairo.

The OFS was designed to hold OLE2 "objects" (files) created by Cairo's Smart Folders and other OLE 2.0 applications. As originally conceived, it would optimize the storage of large numbers of small files, with lower overhead compared to contemporary file systems of the time. Additional APIs would also allow the storage of multiple data streams per-file as well as OLE-specific metadata. The contents and metadata of each file in the file system would be indexed and searchable across Cairo applications. Disk quotas, long file names, ACLs and journaling would also be available.

If enabled across a network, additional functionality such as data replication would allow files to persist across offline and online systems, as well as provide a higher level of fault tolerance. Multiple OFS disks across separate systems could also be joined together by the Distributed File System (DFS) service to create a single superset file system, with users being able to access files across a single namespace.

In combination with metadata-rich Smart Folders, OFS would ultimately allow any type of data (such as regular files, emails, contacts, etc) to be stored on disk or across the network without requiring the need of application-specific databases and protocols. Non-data objects like printers and devices would also be represented under the same hierarchy within Windows Explorer. The concepts explored by OFS would later influence the development of WinFS.

As present in leaked builds, it has support for encryption and file permissions (in a similar manner to NTFS), as well as long filenames. Additional development on OFS was scrapped during the development of Windows NT 4.0. OFS is also included with builds like Windows NT 3.51 build 854.1 that include the  folder.