Installing OSs in the Best Order

OS installation is inherently risky—installers typically include tools to delete and create partitions, create filesystems, install boot loaders, and perform other actions that have the potential to damage or destroy other OSs. Some OSs do a better job of alerting you to dangers or avoiding pitfalls than others. For this reason, installing OSs in a particular order is often desirable and even necessary.

The most common source of problems is with boot loader installation. All OSs include boot loaders. Microsoft provides a very simple boot loader that resides in the disk's Master Boot Record (MBR) at the very start of the hard disk, with secondary code in the boot partition's boot sector. This standard boot loader can boot only one OS, and most Microsoft OSs install the boot loader automatically. (Windows NT, 2000, and XP include a secondary boot loader that can boot other OSs.) Thus, if you install a Microsoft OS after any other OS, chances are your other OS will seem to disappear. You can usually recover from this problem by using an emergency boot system to reinstall the other OS's boot loader in the MBR, or possibly by using DOS's FDISK to change which partition is bootable.

Another problem is partition type codes, which are numbers intended to identify which OS "owns" a partition or what filesystem it contains. Unfortunately, not all partition type codes are unique, which can cause confusion during installation. One such problem is with NTFS (used by Wndows NT, 2000, and XP) and HPFS (used by OS/2), both of which use a partition type code of 0x07. When installing both of these OSs, you must be very careful when installing the second OS so that you do not reformat the just-installed OS's partitions. Using a boot loader's partition-hiding options, if available, can help you avoid problems after installation is complete.

Another problem code is 0x82, which is used both for Linux swap partitions and Solaris installation partitions. You may need to use Linux's fdisk on an emergency or installation boot CD to temporarily change the code of the first OS's 0x82 partitions before installing the second OS.

As a general rule, the best installation order is as follows:

2. Windows 9x/Me

3. Windows NT/2000/XP

4. Solaris or FreeBSD

6. BeOS

7. Linux

I recommend preparing the disk by creating partitions for all of the OSs before you begin actual installation. You can use Linux's fdisk, run from an emergency or installation system, to do this. You'll then let each OS format its own partitions. DOS and Windows may require that the target installation partition be marked as bootable (you can do this using the a command from within Linux's fdisk).

Of course, you must be mindful of partition-formatting options with the later installations—most importantly, never select any option to use an entire hard disk. Most OSs provide options regarding boot loader installation. As you install multiple OSs, you may end up installing one boot loader over another until the end.

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