In planning for Domino 8, it may be possible that you will have to upgrade the Operating System that your Domino 7 (or 6 or earlier) servers are running. For more information, see the detailed system requirements here.
In some of these cases, such as Windows 2000, this is because the Operating System is no longer supported by the vendor. However, there is currently no set EOS date for i5/OS V5R3. However, this is not a supported OS for Domino 8.
The following operating systems are not supported for Domino 8. If you are running one of these with any prior version of Domino, you will need to upgrade the OS to be in a supported configuration for Domino 8. Please note that the latest release levels of all of these platforms are still supported and that it is generally recommended to stay fairly recent on the Operating Systems in your environment. There is also no rip-and-replace involved (as with other messaging platforms) - the most current OS levels were supported for Domino 7.0. So, if you are current on your OS and current on your Domino installation, you will have no issues upgrading to Domino 8. Also, I'm in no way criticizing IBM for this move to only support the latest OS release levels - just making you aware of it for your planning purposes.
OS Platforms Not Supported For Domino 8.0:
Microsoft Windows 2000 Server
Microsoft Windows 2000 Advanced Server
IBM AIX 5.2(4) (64-bit kernel)
Novell SUSE Linux Enterprise Server (SLES) 8
Novell SUSE Linux Enterprise Server (SLES) 9
Sun Solaris 9 (64-bit kernel)
IBM System i
IBM i5/OS, V5R3
IBM System z
IBM z/OS Version 1, Release 5 or later
Linux on System z
SLES 8 & 9