Dual-Boot Installation Restrictions

Various operating systems have restrictions on how they may be placed on the disk. Here is a brief overview of these restrictions for the operating systems discussed here. Note that this sort of information may change rapidly, especially for the open-source operating systems! Also, if you search the Internet, you will find suggestions for getting around all of these limitations. Most of these suggestions are very complicated and unsupportable, and if I recommended them my email would be flooded by people who couldn't make them work. Others cost money. Feel free to seek out these methods and try them yourself, but you're on your own.

OpenBSD

• The root partition must be completely contained within the first 8GB of disk.

• There can only be one OpenBSD MBR partition per hard disk.

Windows (Any Version)

• Must be the first operating system on the hard drive.

Linux, FreeBSD

• None.

Suggested Combinations

Windows operating systems, both 9x-based and NT-based, must go first on the hard drive. I suggest giving these operating systems a C: drive of 7GB or smaller. (Remember, early versions of Windows only support 2GB drives, so this won't be a problem.) If you put a 500MB OpenBSD root file system directly after your Windows partition, you can easily fit it within the 8GB limit. Subsequent OpenBSD file systems should follow immediately afterward. Because OpenBSD can only use a single MBR partition, you need put all your OpenBSD partitions immediately after that. If you have disk space left you can add a third MBR partition to the hard drive after your OpenBSD install and use this for a Windows D: drive or even install Linux or FreeBSD for a triple-boot system.

When installing OpenBSD with FreeBSD or Linux, I recommend putting OpenBSD first on the hard drive and installing the other operating systems further out on the disk.

Windows NT/2000/XP Installs

When you install Windows NT-based operating system, the installer will ask you how much disk space to use on your drive. (This question is the Windows fdisk and disklabel tool, all in one.) Tell it 7GB or less, and Windows will create an appropriate MBR partition for itself.

If you wish to access your Windows files when running OpenBSD, format this Windows file system as FAT32. OpenBSD cannot read NTFS partitions. As you find yourself growing more comfortable with OpenBSD, you will probably find yourself booting into Windows less and less frequently, and being able to access that disk space is nice. I know people who started off with dual-boot systems, but finally converted their Windows partitions into MP3 storage without having to reinstall.

Do not attempt to lay out your OpenBSD partition, or subsequent Windows partitions, with the Windows installer! You will quite possibly confuse OpenBSD, Windows, or both. Similarly, do not attempt to create Windows NT partitions (even FAT32 ones) with the OpenBSD installer. Once you have both Windows and OpenBSD installed, you can go in and create additional Windows logical drives.

Windows 9x installs

While early editions of Windows 95 only handled 2GB partitions, most later versions handle large hard drives just fine and automatically take over all the disk space they can get. Most versions do not ask you how much they should get, as it's obvious that anyone who is running Windows wants to dedicate their whole machine to it, right? You must use a tool such as fips.exe to resize your hard drive.

OpenBSD includes fips.exe in the "tools" directory under the release directory. The documentation included with fips.exe is fairly good, and Windows 9x is becoming increasingly rare among the people likely to be installing dual-boot systems, so we aren't going to go into any detail on how to make it work. Just read the instructions and follow them precicely.

Remember, make your Windows 9x partition no larger than 7.5GB; you want to have enough room to get an OpenBSD root partition on your system!

Linux/FreeBSD Installs

If you are sharing a hard drive between OpenBSD and Linux, install OpenBSD first. Both Linux and FreeBSD can recognize OpenBSD partitions and will easily work around them.

Linux can read OpenBSD file systems, if you have a Linux kernel that supports BSD disklabels. Similarly, OpenBSD can read EXT2FS file systems. OpenBSD also recognizes file systems from FreeBSD 4 or earlier, and FreeBSD recognizes OpenBSD file systems. If you want to dual-boot FreeBSD 5 or later with OpenBSD, you need to create your FreeBSD partitions as UFS1. OpenBSD does not support FreeBSD's UFS2. In any of these combinations, you may have to edit the OpenBSD, Linux, or FreeBSD disklabels to include the sector information for the other operating system partitions to actually be able to mount those partitions, however.