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PCLT
25 Jun 1995
OS/2 comes preinstalled on a bare system when you buy some configurations directly from IBM. Normally, however, systems are shipped with DOS and Windows preinstalled. The most cost effective upgrade is then to buy OS/2 Warp and add it to the system.
If OS/2 is installed onto the C: disk along with an existing DOS system, it will establish a Dual Boot configuration. DOS files will be left in the \DOS directory. The bulk of the OS/2 system will be installed in the \OS2 directory. A few additional utility directories may be created (DESKTOP, SPOOL, NOWHERE, PSFONTS).
Dual boot manages the volatile files in the root directory. In particular, it switches between DOS and OS/2 versions of
During OS/2 installation, the DOS versions of these files are copied to the C:\OS2\SYSTEM directory under the names BOOT.DOS, CONFIG.DOS, and AUTOEXEC.DOS. OS/2 then installs its own boot sector, CONFIG, and AUTOEXEC files in the C:\ root.
Later on, the C:\OS2\BOOT.COM utility can be used to switch between the two operating systems. From OS/2, one switches to DOS with the command:
boot /dos
While from DOS, one switches back using the command:
\os2\boot /os2
Note that the BOOT program is not normally in the DOS path, so it may be necessary to fully qualify the name as \os2\boot so the system can find it.
In either case, the boot utility copies the boot sector record, CONFIG, and AUTOEXEC files of the current operating system to the \OS2\SYSTEM subdirectory, then it restores the saved copies of these files from the other system. When DOS is running, \OS2\SYSTEM has saved files named BOOT.OS2, CONFIG.OS2 and AUTOEXEC.OS2. When OS/2 is running, the *.DOS versions of these files are saved.
The OS/2 system also has a number of hidden system files in the C:\ root directory. They have names that will not cause any conflict with other operating systems.
The Boot Manager utility is installed in its own non-DOS 1 megabyte Primary Partition on the first hard disk. It may be installed anywhere on a SCSI disk. On an IDE disk, it is safest to put Boot Manager somewhere in the first 528 megabytes where the BIOS is certain to be able to find it. The partition into which OS/2 is installed should also be completely contained within the first 528 megs. Newer systems may have a more advanced BIOS that eliminates this restriction. When the Boot Manager is installed it is marked Active/Startable. The installation of another operating system, such as Windows NT, may temporarily disable the Boot Manager. When the installation is done, just mark it Active/Startable again using some version of FDISK/Disk Administration.
The ROM initialization code goes to the Master Boot Record. The MBR sees that the Boot Manager is active, so it loads that program into storage. Boot Manager presents a menu on the screen, and lets the user make a selection or boots the default system if there is no response within a time-out period.
Boot Manager loads another system by reading the first 512 byte sector from the partition or logical volume into storage. Boot Manager can load any system from any volume on any disks, provided that the system is smart enough to initialize properly. OS/2 can be installed on any disk letter and will load under BM.
With Boot Manager, the DOS system can remain on the C: drive. The \OS2 directory and its associated junk (DESKTOP, SPOOL, PSFONTS) are loaded on another volume. The user then selects either DOS or OS/2 from the Boot Manager menu.
It is not necessary to juggle the Boot Sector records. In this configuration, the DOS boot sector is always the first 512 bytes of the C: drive, and the OS/2 boot sector is always the first 512 bytes of another partition or logical volume. The Boot Manager selects a volume and then loads the boot sector from that volume.
The Boot Manager utility is created with the OS/2 FDISK program. The BM partition contains only a minimum amount of information needed to create the menu. If the user is familiar with the system layout, it is fairly simple to delete the Boot Manager and then recreate the partition.
This is necessary because the Boot Manager partition is occasionally corrupted. The easiest way to mess it up is to use Windows NT Disk Administrator or Chicago FDISK, but there is no single bug to avoid. It does not always happen, but it occurs sometimes. The symptom is that the Boot Manager won't run, OS/2 cannot be started, and the OS/2 Installation Diskettes hang when you try to boot them because they recognize the Boot Manager partition but get confused by its contents.
To solve this problem, boot DOS from a floppy. The DOS 6.x FDISK utility may not know about Boot Manager, but it knows that something is in a 1-megabyte non-DOS partition at the end of the disk. Tell DOS FDISK to delete the 1 megabyte non-DOS partition. Now the OS/2 install diskettes will not see a corrupted BM partition. They will load successfully. It will then be possible to run the OS/2 FDISK from the Install floppies to reinstall Boot Manager and reconfigure the menu.
Most people get their DOS and Windows preinstalled on the hard disk by the system vendor. Most system vendors allocate one big C: partition on the hard disk. This is not a good idea, but they do it anyway.
In order to use Boot Manager and to install OS/2 on another disk letter, it would be necessary to scrub everything off the hard disk, repartition it, and then reinstall all the software. This is too much trouble, so users tend to be lazy and just accept the large C: volume. In this environment, the only option is to use Dual Boot. OS/2 can then be installed in the existing C: volume and will coexist with DOS.
What's wrong with this. Suppose the system comes with DOS 6.1 and you add OS/2 Warp. Now IBM gives away a set of disks to upgrade DOS 6.1 to DOS 6.3. The user is supposed to be smart enough to switch back from DOS to OS/2 before installing the upgrade. Unfortunately, this little step gets overlooked. So the DOS 6.3 Upgrade process clobbers the OS/2 boot sector and probably trashes the OS/2 version of CONFIG.SYS. Assuming that CONFIG.SYS is backed up somewhere, the problems can be overcome. However, it is generally an invitation to problems to have two operating systems on the same disk volume with different versions of the same named file.
Boot Manager can put DOS on the C: drive and OS/2 on the D: drive. Upgrades to DOS go to the DOS volume and do not effect the OS/2 system. The system can still get screwed up, but it takes more work to trash things. Boot Manager is the safer and more general solution if you can take the time to repartition the disk.
If someone installs DOS onto a Dual Boot C: drive and clobbers OS/2, it is possible to recover the system without reinstalling. Normally, when DOS is running the OS/2 root files are stored in \OS2\SYSTEM under the names BOOT.OS2, CONFIG.OS2, and AUTOEXEC.OS2. When OS/2 is running, the DOS versions of the files are stored in the same place as BOOT.DOS, CONFIG.DOS, and AUTOEXEC.DOS. However, in this configuration BOOT.OS2 is not deleted. It may, however, be marked as "Hidden", so it will only show up in a DIR listing using the /A switch.
So if DOS is installed on top of OS/2, the problem is that the C:\ root has DOS files and the C:\OS2\SYSTEM directory also has DOS files. Assuming that the OS/2 versions of CONFIG and AUTOEXEC have been saved somewhere, the trick is to copy them back into \OS2\SYSTEM as CONFIG.OS2 and AUTOEXEC.OS2. Then unhide the BOOT.OS2 that is already in the directory. Now you have a saved OS/2 system ready to be restored, and can use the "boot /os2" command to switch systems again.
An IBM employee has written a package to build bootable diskettes from you OS/2 system. It is called BOOT2X and is available on various bulletin board systems or from Almaden or Watson .
The short answer is "Only by reformatting all the volumes" but in practical terms it is not quite that bad. The OS/2 system itself consists of:
The boot sector can be overwritten and the other files and directories can be deleted. If these files are deleted while running a copy of OS/2 (say by booting off the Install diskettes and then deleting the files) then the Extended Attributes for the deleted files will be removed. If OS/2 was installed in a FAT partition, then these directories can be deleted under DOS. However, DOS is not smart enough to delete the Extended Attributes as it deletes the files and directories.
Before installing OS/2 on an old disk, it is a good idea to run the OS/2 CHKDSK program to clean up any problems. Rather than relying on the standard script, load the Install diskettes and run the program manually. The new OS/2 will inherit Extended Attributes defined for any of the remaining directories and files, but since they belong to applications they will not effect the correct function of a subsequent operating system.
Copyright 1995 PC Lube and Tune -- Das Boot -- H. Gilbert