Newsgroups: comp.sys.ibm.pc.hardware Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!linus!linus!mwunix.mitre.org!jcmorris From: jcmorris@mwunix.mitre.org (Joe Morris) Subject: Re: Partition table Message-ID: Sender: news@linus.mitre.org (News Service) Nntp-Posting-Host: mwunix.mitre.org Organization: The MITRE Corporation, Bedford MA References: Date: 4 Apr 91 13:46:59 GMT achilles@unixland.uucp (David Holland) writes: >Owing to some recent computer trouble I've been poking somewhat deeper into >my system than usual, and I noticed the following interesting oddity about >the partition table: there are only two partitions listed, one of which is >twice as large as the other, and only one of them is marked DOS. The disk >contains three equal-sized partitions, all of which are DOS; where is this >information stored? Or does Norton's partition-table editor mislead me? The documentation for Norton (at least at 4.5; I haven't had to look it up in the 5.0 doc) isn't clear on the structure of a (physical) disk with multiple partitions. If you have a single physical disk with three DOS partitions filling it, the partition table as shown by Norton will display only the first DOS partition and a second partition marked "EXTENDED". If you read the starting location of the EXTENDED partition from the display and then display *that* record (using F6 to display it as a partition table) you'll find that this partition table has one DOS partition and one extended partition. Chain to the start location of this second extended partition and display it; you'll see a partition table with only a DOS partition. The three partition tables marked as DOS partitions are the C, D, and E drives; the extended partitions cover the space occupied by all lower partitions. I don't recall ever seeing it documented but apparently you can't have two DOS partitions in the same partition table. Here's what your disk should look like: Master Partition Real Disk Drive Table (cyl 0 head 0 record 1): < - - - - - - - - - - - - | \ V \ Start real disk \ C0:H0:R1 DOS-16 - - - - - - - - - - - - - - - - - -> Start C: EXTENDED \ \ \ \ \ \ \ \ \ \ \ . \ \ \ \ \ \ \ \ \ \ \ . \ - - - - - - - - -> End C: \ - - - - - - - - - - - - - - - -> Start First Extended Partition Second Partition - - - - - - -> Start D: Table (-> by MPT) / / / / / / / / | // / / / / / / / V / / / / / / / / / // / / / / / / / / DOS-16 - - - - - - - - - - - - -> End D: EXTENDED - - - - - - - - - - - -> Start Second Extended Partition Third Partition - -> Start E: Table (-> by 2nd PT) // / | / / / V // / / / / / / DOS-16 - - - - - -> End E: End second ext. part. End first ext. part End real disk Note that the four last lines (the end of E:, the end of the two extended partitions, and the end of the real disk) all occur at the last track of the last cylinder of the physical disk. Note also that the partition table in each partition is located at the first record on the first track of the first cylinder in that partition. In effect this is the same rule as is used for the master partition table, which is always on the first record of the physical disk. Also, note that the master partition table occupies the same record (0/0/1) as the master boot record. Quiz on Friday. Joe