4D Server or 4th Dimension will run on either NT 4.0 Workstation or NT 4.0 Server. Bug fixes have been released by Microsoft for both these products. These bug fixes correct a variety of problems including security breaches that have been discovered to exist in the NT product(s). The releases are called by Microsoft Service Packs.
Which Service Pack should I use?
There were two service packs that have been released that are acceptable. At the bare minimum you should have installed Service Pack 3. There were known problems using 4D Server or 4th Dimension and not having Service Pack 3 installed.
Microsoft introduced Service Pack 4 which caused more problems than it fixed. Service Pack 5 was released very shortly after Service Pack 4. After extensive testing I find no problems with 4D and Service Pack 5. Since Service Pack 5 fixed some substantial security holes that were found in Service Pack 3, I would recommend you switch to SP5.
For a list of bugs fixed from SP3 to SP5 visit https://support.microsoft.com/support/kb/articles/Q225/0/37.ASP
You can download service pack 5 at https://www.microsoft.com/ntserver/nts/downloads/recommended/sp5/default.asp?RLD=16
Before you jump to installing SP5, I suggest that you check up on the other known problems with SP5. To see if you run into any of those. Some have work arounds posted on Microsoft's Web site. However, for most purposes you won't probably be running some of the programs where known problems with SP5 exist on the same machine as your 4D Product. (Exchange, SQL Server) Believe it or not there is even a SP5 patch that was released July 1, 1999 for MSDN Subscribers.