Requirements to Boot Previous Operating System (121963)

CAUSE

This behavior can be caused by any of the following conditions:

The line "BootMulti=1" is not present in the Msdos.sys file in the root folder of the boot drive. If drive C is compressed, this line must be present in the Msdos.sys file located on the host drive for drive C (instead of in the Msdos.sys file located on drive C).
You did not install Windows 95 over Microsoft MS-DOS version 5.0 or later, or IBM PC-DOS version 5.x or 6.x. You must install Windows 95 over one of these MS-DOS or PC-DOS versions in order to boot your previous operating system after installing Windows 95.
The system files from your previous operating system are missing or damaged.

RESOLUTION

To resolve this issue, use the appropriate method:

Add the line BootMulti=1 to the Msdos.sys file in the root folder of the boot drive. To do so, follow these steps:
1. Type the following line at a command prompt, and then press ENTER:
  attrib c:\msdos.sys -s -h -r
  NOTE: If drive C is compressed, use the ATTRIB command to modify the Msdos.sys file located on the host drive for drive C instead of the Msdos.sys file located on drive C.
2. Use any text editor (such as Notepad) to open the Msdos.sys file.
  
  NOTE: If drive C is compressed, edit the Msdos.sys file located on the host drive for drive C instead of the Msdos.sys file located on drive C.
3. Add the following line to the [Options] section of the file, if the line does not already exist:
  BootMulti=1
4. Save and then close the Msdos.sys file.
5. Type the following line at a command prompt, and then press ENTER:
  attrib c:\msdos.sys +s +h +r
  NOTE: If drive C is compressed, use the ATTRIB command to modify the Msdos.sys file located on the host drive for drive C instead of the Msdos.sys file located on drive C.
Use a bootable floppy disk that starts your previous operating system to restore the system files from the previous operating system. To do so, follow these steps:
1. Remove the Hidden, System, and Read-Only attributes from the MS-DOS Io.sys and Msdos.sys files on the floppy disk. To do so, type the following commands at a command prompt, pressing ENTER after each command
  attrib <drive>:\io.sys -s -h -r attrib <drive>:\msdos.sys -s -h -r
  where <drive> is the drive letter of the floppy disk drive contain- ing the bootable floppy disk.
2. Copy the MS-DOS system files from the floppy disk to the root folder of the boot drive. To do so, type the following commands from a command prompt, pressing ENTER after each command
  copy a:\io.sys <boot>:\io.dos copy a:\msdos.sys <boot>:\msdos.dos copy a:\command.com <boot>:\command.dos
  where <boot> is the drive letter of the boot drive.
3. Remove all floppy disks from the disk drives, and then restart the computer.

NOTE: If you did not install Windows 95 over Microsoft MS-DOS version 5.0 or later, or IBM PC-DOS version 5.x or 6.x, you cannot boot your previous operating system.

MORE INFORMATION

Booting Previous Operating System Without Restarting Computer

To boot your previous operating system after installing Windows 95 in a new folder, you must restart the computer. You cannot switch between Windows 95 and your previous operating system without restarting the computer.

Dual-Booting MS-DOS 5.x or Later or PC-DOS 5.x or 6.x

Versions of MS-DOS earlier than 5.0 require that the first three sectors of the Io.sys file reside in the first three sectors of the data area of the hard disk. MS-DOS versions 5.0 and later do not have this requirement. It is this flexibility that allows you to dual-boot between Windows 95 and an earlier version of MS-DOS or PC-DOS.

When you install Windows 95 on a computer running MS-DOS version 5.0 or later, Setup preserves the Io.sys, Msdos.sys, Command.com, Autoexec.bat, and Config.sys files from your previous operating system by renaming them to Io.dos, Msdos.dos, Command.dos, Autoexec.dos, and Config.dos. If you choose to install Windows 95 in a new folder, Setup automatically adds the line "BootMulti=1" to the Msdos.sys file so that the computer can dual- boot Windows 95 and MS-DOS. If the Io.dos, Msdos.dos, or Command.dos file is removed from the computer, moved to a folder other than the root folder of the boot drive, or becomes damaged, you cannot boot your previous operating system.

Booting MS-DOS on a Computer with Preinstalled Windows 95

Most original equipment manufacturers (OEMs) do not install Windows 95 over an existing copy of MS-DOS. If the version of Windows 95 that you use came preinstalled on a new computer that you recently purchased, the MS-DOS system files are most likely not present on your hard disk.

Running a Previous Version of Windows or Windows for Workgroups

If you installed Windows 95 in a new folder, you can run your previous version of Windows or Windows for Workgroups after booting your previous operating system. If you upgraded your earlier version of Windows to Windows 95, you cannot run your previous version of Windows. To run your previous version of Windows if you installed Windows 95 in a new folder, boot your previous operating system, and then run your previous version of Windows from the command prompt.

Booting a Previous Operating System Is Not Supported in OSR2

Windows 95 OEM Service Release 2 (OSR2) is designed to be preinstalled on new computers only, and cannot boot back into Windows 95 from a previous operating system. If you format the hard disk, install MS-DOS, install OSR2, boot the previous operating system, and then try to reboot to Windows 95, the computer stops responding (hangs).

For additional information, see the following article in the Microsoft Knowledge Base:

155364 OSR2 Hangs After Booting Previous Operating System

PC-DOS is manufactured by IBM, a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding this product's performance or reliability.