>A prospective customer is asking me for "Minimum NOS level, for example, windows server 2003 or 2008". I tried to Google but get all kind of unrelated results. What is the NOS level? What are the reasonable values (just to give them some numbers)?

Possibly "Network Operating System", which could be either:

- OS of the network primary domain controller (PDC). Important if your app makes use of Active Directory
- OS of a member server on which your apps or data will reside

There is a list of Windows Server versions at http://en.wikipedia.org/wiki/Windows_Server .

Since Windows 2000, server and workstation versions are basically the same, it's just that the workstation versions have some restrictions, and features removed i.e.

Server 2003 -- same code base as XP RTM/SP1
Server 2003 R2 -- same code base as XP SP2/SP3
Server 2008 -- same code base as Vista
Server 2008 R2 -- same code base as 7
Server 2012 -- same code base as 8
Server 2012 R2 -- same code base as 8.1

Microsoft is only supporting Windows versions back to Server 2003/XP (support for XP ends April 8, 2014).