Potential Problems with and Limitations of Dual Boot Systems
It is possible to have a dual boot system in which you can have two (or even more) operating systems on the hard disk, and you can select which one you want at each system boot. There are some potential problems that you need to be aware of when doing this, though.
The first one is that all of the information necessary to boot FreeBSD must be located within the first 1024 cylinders of the hard disk. This means that either the root partition must be completely located within the first 1024 cylinders, or you can use a separate boot partition that is completely located in the first 1024 cylinders. If you choose this option, the root partition does not have to be completely located in the first 1024 cylinders. Note that "completely located" means that the partition has to both start and end below the 1024th cylinder. Simply starting below the 1024th cylinder is not good enough.
If you need more space for Windows or DOS than is available below 1024 cylinders, you will need to split the Windows or DOS partition into two partitions, giving you a C drive and a D drive in Windows or DOS. In between these C and D drives, you will need to put a small partition for FreeBSD to boot from. This partition will be used as /boot later on during the install. 30 megabytes should be more than enough for this partition.
The second thing to be aware of if you will be reinstalling everything is that you should install DOS or Windows before you install FreeBSD. DOS and Windows assume that they are the only operating system on the hard drive, and will overwrite the master boot record without asking. If you install FreeBSD first, installing DOS or Windows later will clobber FreeBSD's boot manager, and you will no longer be able to boot into FreeBSD. This problem is easily fixed, but save yourself the headaches, and just install DOS or Windows first.
Dual Booting with DOS, Windows 95, Windows 98, or Windows ME
FreeBSD comes with a boot manager that will allow you to dual boot with various operating systems. If you already have DOS, Windows 95, Windows 98, or Windows ME installed, it is easy to set up the boot manager. You will be given the option to install it during the FreeBSD installation. DOS, Windows 95, Windows 98, or Windows ME will automatically be added to the boot menu.
Dual Booting with Linux
If you wish to dual boot with Linux and load Linux from the FreeBSD boot manager, install LILO at the beginning of your Linux boot partition rather than in the MBR. See the LILO documentation for instructions on how to do this. After you have done this, you will be able to boot Linux from the FreeBSD boot manager. If you wish to boot FreeBSD from LILO, please see the section later in this chapter titled "Booting FreeBSD from LILO," later in this chapter.