What hardware specs are needed for a website which gets 2000 simultaneous users at a time ?
It will be a dedicated server for sure but what specs such as ram, cpu, ssd? network?
2,000 simultaneous users of what? Static pages with some self-hosted image and video? Data-driven webpages with multimedia contents served by CDN? Average MMORPG? IRC node?
I'm afraid it's impossible to say without some of that detail.
This type of question is kinda scary. It is either some homework question or someone who thinks they can click some box that says "make internet server". There is no simple answer without a lot of details. The question almost answers itself once you collect the detailed information behind the question.