My understanding is that on Multics, segment = file.
Multics had a segmented memory model, much like segmented memory models on the 286 and 386 – indeed, Multics was one of the influences on the designers of the 286 and 386 – although newer x86 operating systems moved to flat memory model instead, so segmented memory only ever saw significant use on 16-bit versions of Windows and OS/2.
What made Multics unique was that all files were mmaped – opening a file gave you the ID of a memory segment, which you'd then use much as you'd use a segment selector on x86.
segment
User-visible subdivision of a process's address space, mapped onto a storage system file. Each segment is 1MB long, and has a zero address. The term "segment" is used interchangeably with "file" -- except not really: the things that are files in other systems are implemented as segments; also, the term "file" includes multi-segment files, and when talking in terms of COBOL, PL/I, or FORTRAN language runtime objects, one speaks of files. Programs are spoken of as stored in (procedure) segments. Correct use of the terms "file" and "segment" is a sure sign of a Multician.
Multics had a segmented memory model, much like segmented memory models on the 286 and 386 – indeed, Multics was one of the influences on the designers of the 286 and 386 – although newer x86 operating systems moved to flat memory model instead, so segmented memory only ever saw significant use on 16-bit versions of Windows and OS/2.
What made Multics unique was that all files were mmaped – opening a file gave you the ID of a memory segment, which you'd then use much as you'd use a segment selector on x86.