Files-11 On-Disk Structure Specification

This document specifies the on-media structure used by Files-11, a general-purpose file structure intended for PDP-11 systems. It focuses on structure level 2 (ODS-2), which offers improvements over structure level 1. The document details conventions for numerical values and data formatting, describes the concepts of medium, volume, and volume sets, and then extensively elaborates on the structure and attributes of files, including file headers, various areas within headers (ident, map, access control, reserved, checksum), file IDs, and file types (multi-header, multi-volume). It also covers directories, their organization, protection, and structure, as well as various file system control files like the index file, storage bitmap file, bad block file, and master file directory. Additionally, the document explains different file organizations supported by Record Management Services (RMS) such as Sequential, Relative, and Indexed, and delves into data formats and representations for strings, binary values, pointers, and packed decimal strings. It further describes the structure of buckets, index records, data records, and the use of record reference vectors. Finally, it details the prologue blocks, key descriptors, and area descriptors used in Indexed file organizations.