1.DSP is demand side platform which is a buyer side platformDCM is DoubleClick campaign manager which is an ad server for advertisers
2.DSP helps to manage multiple ad exchanges, ad networks or sites using one interface.DCM helps advertiser or agencies to create tags or trackers by which they can track their campaign performance and status of delivery
3.Advertiser can bid for their target users on an open forumAdvertiser can create multiple tags or tracker to track multiple events taken by user on the ad
4.DSP is a web-based tool used for real-time buying of impressionsIt is a web-based tool used for ad management
5.A DSP ‘plugs in’ to an ad exchange where publishers make their inventory availableDCM has no role in real-time bidding directly and is only responsible for sharing tags as per requirement after which it helps in reporting
6.There are multiple DSP’s where DBM (DoubleClick Bid manager) is Google’s DSPDCM is a tool provided by Google