Yes. Your BO ID links all your Demat holdings across securities like equities, bonds, ETFs, etc., and is used by back-office tools and apps to generate portfolio reports.

There is no regulatory cap. You can open multiple Demat accounts (and hence multiple BO IDs) with different DPs/brokers, provided you comply with KYC norms.

In CDSL, the 16-digit BO ID is numeric and directly used. In NSDL, the BO ID is alphanumeric and starts with ‘IN’, followed by 14 digits.