what we can do in SITE that we can not do in Portals?
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In simple words, Portal users do not need Appian User accounts and can access the information available on portal just with the use of URL. When it comes to Site the user needs to be part of the Appian groups and hence an Appian user account is needed.
Thanks for your response, i am aware about this apart from this what can we do in Site that we can not do in portal is there anything which we can perform in site and not in portals?
Sure. Pages in a site can be reports, actions, records and interfaces. Portals do only support interfaces.