There are also a lot of «lightweight nodes» which do not download entire blockchains but rather verify transactions by downloading the associated block headers. (cryptotimes.news)
«Long before the network gets anywhere near as large as that, it would be safe for users to use Simplified Payment Verification (section 8) to check for double spending, which only requires having the chain of block headers, or about 12 KB per day. (coindesk.com)
If MasterCard wants to achieve its idea, it has to make sure that the suggested system includes «fast track flags» in block headers. (coinidol.com)