server spec for Active Directory server with 1000+ users ... just users no dhcp or dns invovle.

That many users and only one server and no DNS?!? You sure about that???

Do you also need roaming profile for them and store them in same server ? If no then windows 2012 Std with 8GB RAM and 4 Core CPUs would be sufficient for smooth operation.

Also is this single domain in single DC ?

You do realize that Active Directory REQUIRES DNS.  And not just any DNS - it requires a DNS that supports Service Records and Dynamic Updates.  And are you suggesting that you're introducing Active Directory into an environment that never had it before?  Because odds are a single core single CPU with 2 GB of RAM would service it fine too.  AD is a VERY light weight service (I used to run 1000 users on a singe system (well, two, but when I looked at the CPU usage, it was near ZERO and it was never struggling for RAM).

thank you all... yes it is being installed at a site that never had it before... ok. DNS but not dhcp. with that being said, would single core single CPU with 2 GB of RAM still good?

no roaming profile and yes single domain, Chirag Nagrekar

I prefer 4 in most scenarios these days  AD is lightweight but windows is greedy with any role.

With that said, I'd still do two servers.  It for load reasons, but with that many users, any mishap with a domain controller can be expensive. Redundancy is extremely important at that scale. Only very small businesses should consider running a single DC, in my opinion. On two separate physical machines (even if they are VMs on those two physical machines.)

Thank you, Cliff.
this is a small company which will be expanded down the road.  This AD server will only to host our cloud based users.  right now, our users are in 100's but just a pro active thinking for 1000 users.

That's still a good reason for two servers.

Agreed on all counts. Just to clarify, at "100s" of users, that's not small by most definitions. And while a restore is fine for 10 users, having 250 employees twiddling their thumbs for even an hour Monday morning while a DC restored is a ton of lost man-hours. 6 weeks of man hours lost isn't trivial. At that size, I still think 2 DCs is almost mandatory, along with the requisite knowledge/education to manage them.

awesome inputs everyone!  if your professional opinion, virtual vs. physical.  I've played with virtual quiet...

thanks