OS/2 Warp Version 4
The fourth major release of the client version of the OS/2 operating system and also known under the original project name OS/2 Merlin or just plain "Merlin". It is not as radical a change as OS/2 Version 3 was from OS/2 Version 2 mainly because the money earmarked for OS/2 development inside IBM's Personal Systems Division was used to develop the ill-fated OS/2 PPC, and while small portions of the OS/2 PPC code showed up in Merlin, most of the changes were superficial.
Minor versions
IBM released versions 4.5 for those with a defect support contract and for a time also sold it as a upgrade. This has numerous fixes and updates introduced in the OS/2 4.5 server version.