Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!usc!ucsd!helios.ee.lbl.gov!nosc!cod!desmond
From: desmond@cod.NOSC.MIL (J. Desmond)
Newsgroups: comp.sys.ibm.pc
Subject: DOS Structure on Hard Disk - A Question
Keywords: DOS, boot record, FAT, confusion, cold fusion
Message-ID: <1626@cod.NOSC.MIL>
Date: 1 Sep 89 16:52:23 GMT
Organization: Naval Ocean Systems Center, San Diego
Lines: 45



            Recently, out of curiosity, I started to take a deep look at
      how DOS is structured on my hard disk.  All the manuals say that the
      boot record is the absolutely no kidding very first thing on the
      disk.  And that's exactly what shows up with DEBUG and NORTON U's
      when I specify the lowest numbered sector available.  I felt
      reassured.  Today I found several low level sector editors and took
      them for a spin and nearly drove off the edge of the world!  There,
      before the boot sector, was an entire track with more stuff on it.
      The editor said that the boot sector began at cylinder 0, head 1,
      sector 1 but woke up looking at C0,H0,S1 which contained code and
      some ascii such as "Bad part. table" and "Hard drive I/O error" and
      "No DOS on disk".  The rest of the track seems to be all zeros.
      Anybody out there able to explain what this stuff is, how and when it
      gets there, and how programs might access it and why (i.e. do PC
      locking programs mess with it and does DOS care?)

      Here's my basic disk information:

      OEM Name and Version: ZDS  3.0

      Information for Drive C:
            512 Bytes/Sector
              4 Sectors/Cluster (2048 Bytes/Cluster)
             17 Sectors/Track
              4 Heads on Disk

         Total Disk Capacity is 41463 Sectors
                      including     1 Boot Sector
                                   82 FAT Sectors
                            and    32 Root DIR Sectors

         Storage Capacity is 21170176 Bytes
                                41348 Sectors
                                10337 Clusters

         The disk contains 2 FAT's of 41 sectors each, using 16 bit FAT entries
         The disk's root directory occupies 32 sectors and can hold 512 files



      Thanks.
      -John M. Desmond
      desmond@nosc.mil