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Everything about Volume Table of Contents

In the storage architecture of OS/360 and successors, CMS, and DOS/360 and successors, the Volume Table of Contents (VTOC) is a data structure that provides a way of locating the data sets that reside on a particular DASD volume. With the exception of the IBM Z compatible disk layout in Linux on Z, it is the functional equivalent of the MS/PC DOS File Allocation Table (FAT), the NTFS Master File Table (MFT), and an inode table in a file system for a Unix-like system. The VTOC is not used to contain any IPLTEXT and does not have any role in the IPL process, therefore does not have any data used by or functionally equivalent to the MBR. It lists the names of each data set on the volume as well as size, location, and permissions. Additionally, it contains an entry for every area of contiguous free space on the volume. The third record on the first track of the first cylinder of any DASD volume is known as the volume label and must contain a pointer to the location of the VTOC. The location of the VTOC may be specified when the volume is initialized. For performance reasons it may be located as close to the center of the volume as possible, since it is referenced frequently. A VTOC is added to a DASD volume when it is initialized using the Device Support Facilities program, ICKDSF, in current systems. Wikipedia →

🧭 Start here: a 6-step reading path

  1. Read the overview: Volume Table of ContentsA 5-minute orientation
  2. Skim a recent paper: IJIKM Volume 19, 2024 – Table of ContentsInfluential work since 2022
  3. Pick up a classic book: Laws, etcThe most-reprinted book on the subject
  4. Read the landmark paper: Volume Table of ContentsCited 0 times
  5. Go sideways: Channel I/OA closely related topic
  6. Go sideways: Support programs for OS/360 and successorsA closely related topic

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🗂️ The subject at a glance

  1. Data Set Control Block types

🏆 Landmark papers (most cited)

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