Path: utzoo!mnetor!uunet!portal!cup.portal.com!truett
From: truett@cup.portal.com
Newsgroups: comp.sys.ibm.pc
Subject: Re: Need info - Using large capacity hard disk w/MS-DOS
Message-ID: <3093@cup.portal.com>
Date: 10 Feb 88 09:15:07 GMT
References: <5561@sgistl.SGI.COM> <4583@ecsvax.UUCP>
Organization: The Portal System (TM)
Lines: 44
XPortal-User-Id: 1.1001.2190


With regard to MS-DOS being able to handle multiple partitions on a hard disk:

1) Up through version 3.2 of PC-DOS and most varieties of MS-DOS, only a
   single DOS partition could be created by FDISK.  It was always possible
   to have partitions for other operating systems on a drive.  Note that the
   single DOS partition was limited to a size of 32 MB.

2) The term "active partition" refers to which partition is BOOTABLE.  Just
   the fact that a DOS partition exists on a drive does not mean that it is
   the DOS partition from which the machine performs a hard boot.  In fact,
   it is possible for a machine to have a hard drive none of whose partitions
   are bootable.

3) As of PC-DOS version 3.3, the supplied FDISK program can create more than
   one DOS readable partition.  Each is still limited to 32 MB and only one
   can be "active", i.e., bootable, at any time.

4) It is possible, using third-party software, to create DOS readable
   partitions which are larger than 32 MB.  Programs that do this include
   VFeature, Speedstor, and Disk Mechanic.  I believe the Mace Utilities can
   also do this.

5) As far as I know, none of these can create a DOS bootable (active) partition
   which is larger than 32 MB.  Thus, the usual practice is to create a small
   DOS boot partition (say 1-2 MB) and either put all the rest of the drive
   into a single large DOS readable partition or split the drive up as desired.
   Some programs are limited in the number of partitions they can handle on a
   single drive; I have seen as many as 16 on a single hard drive.  Note that
   the partition table created by the DOS version of FDISK only has room for
   four entries.

6) When you get to really BIG disks, like some of the optical disks with more
   than a Gigabyte on each surface, then things get more complicated.  In such
   cases, it is necessary to "mount" the partitions that are to be currently
   accessible and ~dismount" them when you are through.  This is because DOS is
   totally incapable of dealing with file allocation and directory data for
   such a vast disk space.  (As an aside, I understand that some versions of
   UNIX, with a 65K limit on the number of entries in the inode table for a
   device, has problems with really big disks.)

Hope this is helpful.

Truett Lee Smith, Sunnyvale, CA
UUCP:  truett@cup.portal.com