The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system

The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. Our efforts emphasize portability, standardization, correctness, proactive security and integrated cryptography.

OpenBSD supports binary emulation of most programs from SVR4 (Solaris), FreeBSD, Linux, BSD/OS, SunOS and HP-UX. OpenBSD is freely available from our FTP sites, and also available in an inexpensive 3-CD set.

Updates (via Distrowatch):

Theo de Raadt has announced the release of OpenBSD 4.8. Some of the more interesting improvements in hardware support and software updates of this release include: "ACPI-based suspend/resume works on most machines with Intel/ATI video, machines using NVIDIA graphics will not resume the graphics; OpenSSH 5.6 with many new features and bug fixes; Mandoc 1.10.5, a utility used to build all manuals in the base system and in Xenocara from mdoc and man sources; over 6,400 ports, major robustness and speed improvements in package tools; package highlights - GNOME 2.30.2, KDE 3.5.10, Xfce 4.6.2, MySQL 5.1.48, PostgreSQL 8.4.4, Postfix 2.7.1, Mozilla Firefox 3.6.8 and 3.5.11, OpenOffice.org 3.2.1, PHP 5.2.13, major components - Xenocara (based on X.Org 7.5 with X.Org Server 1.8 + patches, FreeType 2.3.12), GCC 2.95.3, 3.3.5 and 4.2.1 + patches, Perl 5.10.1, our improved and secured version of Apache 1.3, with SSL/TLS and DSO support...." See the OpenBSD 4.8 release page for more details. Download: i386/install48.iso (212MB, SHA256), amd64/install48.iso (225MB SHA256).

OpenBSD has long been respected for its simple and straight forward installation process, which is consistent across all platforms.
All platforms use a very similar installation procedure, however there are some minor differences in details on a few platforms. In all cases, you are urged to read the platform-specific INSTALL document in the platform directory on the CD-ROM or FTP sites (for example, i386/INSTALL.i386, macppc/INSTALL.macppc or sparc/INSTALL.sparc).
The OpenBSD installer is a special kernel with a number of utilities and install scripts embedded in a pre-loaded RAM disk. After this kernel is booted, the operating system is extracted from a number of compressed tar(1) (.tgz) files from a source other than this pre-loaded RAM disk. There are several ways to boot this install kernel:

Floppy disk: OpenBSD can be installed on many platforms by booting an installer from a single floppy disk. However, due to space constraints, some larger platforms (sparc64, amd64, alpha) do not have some utilities which may be important to you, such as a DHCP client to configure the network. For these platforms, you may do better with the CD install. However, for platforms like i386 and sparc, you will find the boot floppy very complete. Floppy disk images are provided which can be used to create an install floppy on another Unix-like system, or on a Windows system. Typical file names are floppy48.fs, though several platforms have multiple floppy images available.
CD-ROM: On several platforms a CD-ROM image (cd48.iso for just booting, or install48.iso for the entire install) is provided allowing creation of a bootable CD-ROM.
Existing partition: The RAM disk kernel can be booted off an already existing partition for an upgrade or reinstall.
Network: Some platforms support booting over a network (for example using PXE or other network boot).
Writing a file system image to disk (miniroot): a filesystem image that can be written to an existing partition, and then can be booted.
Bootable Tape: Some platforms support booting from tape. These tapes can be made following the INSTALL.platform instructions.

Not every platform supports all boot options:

alpha: Floppy, CD-ROM, network, writing a floppy image to hard disk.
amd64: Floppy, CD-ROM, network.
armish: Varies by machine.
hp300: CD-ROM, network.
hppa: Network.
i386: Floppy, CD-ROM, network.
landisk: miniroot, installed using another computer.
macppc: CD-ROM, network.
mvme68k: Network, bootable tape.
mvme88k: Network, bootable tape.
sparc: Floppy, CD-ROM, network, writing image to existing swap partition, bootable tape.
sparc64: Floppy (U1/U2 only), CD-ROM, network, writing image to existing partition.
vax: Floppy, network.
zaurus: Boot bsd.rd from Linux partition. See INSTALL.zaurus for details.

All platforms can also use a bsd.rd to reinstall or upgrade.
Once the install kernel is booted, you have several options of where to get the install file sets. Again, not every platform supports every option.

CD-ROM: Of course, we prefer you use the Official CD-ROM set, but you can also use install48.iso or you can also make your own.
FTP: Either one of the OpenBSD FTP mirror sites or your own local FTP server holding the file sets.
HTTP: Either one of the OpenBSD HTTP mirror sites or your own local web server holding the file sets.
Local disk partition: In many cases, you can install file sets from another partition on a local hard disk. For example, on i386, you can install from a FAT partition or a CD-ROM formatted in ISO9660, Rock Ridge or Joliet format. In some cases, you will have to manually mount the file system before using it.
NFS: Some platforms support using NFS mounts for the file sets.
Tape: File sets can also be read from a supported tape. Details on creating the tape are in the INSTALL.platform document.

Pre-installation checklist.
Before you start your install, you should have some idea what you want to end up with. You will want to know the following items, at least:

Machine name
Hardware installed and available
- Verify compatibility with your platform's hardware compatibility page
- If ISA, you also need to know hardware settings, and confirm they are as OpenBSD requires.
Install method to be used (CD-ROM, FTP, etc.)
Should an important bug be found, how will the system be patched?
- If done locally, you will need to have sufficient space available for the source tree and building it.
- Otherwise, you will need access to another machine to build a patched release on.
Desired disk layout
- Does existing data need to be saved elsewhere?
- Will OpenBSD coexist on this system with another OS? If so, how both will be booted? Will you need to install a "boot manager"?
- Will the entire disk be used for OpenBSD, or do you want to keep an existing partition/OS (or space for a future one)?
- How do you wish to sub-partition the OpenBSD part of your disk?
Network settings, if not using DHCP:
- Domain name
- Domain Name Server(s) (DNS) address
- IP addresses and subnet masks for each NIC
- Gateway address
Will you be running the X Window System?

Creating bootable OpenBSD install media.
As examples, we will look at the installation images available for the i386 and sparc platforms.
The i386 platform has six separate installation disk images to choose from:

cd48.iso is an ISO9660 image that can be used to create a bootable CD with most popular CD-ROM creation software on most platforms. This image has the widest selection of drivers, and is usually the recommended choice if your hardware can boot from a CDROM.
cdemu48.iso is an ISO9660 image, using "floppy emulation" booting, using a 2.88M floppy image. It is hoped that few people will need this image -- most people will use cd48.iso, only use cdemu48.iso if cd48.iso doesn't work for you.
install48.iso is an ISO9660 image, containing all the standard install files. This file can be used to create a CD that can do a stand-alone OpenBSD install.
floppy48.fs (Desktop PC) supports many PCI and ISA NICs, IDE and simple SCSI adapters and some PCMCIA support. Most users will use this image if booting from a floppy
floppyB48.fs (Servers) supports many RAID controllers, and some of the less common SCSI adapters. However, support for many standard SCSI adapters and many EISA and ISA NICS has been removed.
floppyC48.fs (Laptops) supports the CardBus and PCMCIA devices found in many laptops.

The sparc platform has four separate installation disk images to choose from:

floppy48.fs: Supports systems with a floppy disk.
cd48.iso An ISO image usable to make your own CD for booting SPARC systems with a CD-ROM.
miniroot48.fs Can be written to a swap partition and booted.
install48.iso is an ISO9660 image, containing all the standard install files. This file can be used to create a CD that can do a stand-alone OpenBSD install.

On modern platforms, you are best advised to use the CDROM boot images, as in some of the "bigger" platforms (such as amd64, sparc64), the floppy images have had to have a lot of drivers and utilities cut out, which can make installation much more difficult. Older platforms, such as i386 and sparc, are still quite installable from floppy.

Screenshots.

-->