> TCP/IP as implemented in 1983 was very different from how it is implemented today
The gap between 1983 TCP/IPv4 and 2019 TCP/IPv4 is arguably smaller than the gap between 1982 NCP and 1983 TCP/IPv4.
For example, data flow in an NCP connection is one-directional, meaning that applications wanting bidirectional communication have to use a pair of connections, whereas TCP allows communication in either direction over the same connection.
A 1983 TCP/IPv4 stack probably could successfully communicate with a 2019 TCP/IPv4 stack, although changes in TCP congestion algorithms, MTU discovery, etc would likely cause significant performance issues over long-distance links. TCP/IP and NCP are completely incompatible protocols so TCP/IP-only host could not communicate with an NCP-only host at all.
Good points. A better analogy might be switching an entire LAN from token-ring to ethernet. The LAN is identical, despite the fact that the new network is incompatible with the old.
The nodes in 1982 and 1983 were largely the same, so if you look at the internet as the nodes, then there is continuity, but if you look at the internet as compatible intercommunicating protocols, then there is not.
The human side might help. The point where the actual network of connected hardware actually started to affect human society. All of the key ingredients for what is around today, but not necessarily the same hardware and software - because that has changed dramatically but not the scope of the problem space.
The gap between 1983 TCP/IPv4 and 2019 TCP/IPv4 is arguably smaller than the gap between 1982 NCP and 1983 TCP/IPv4.
For example, data flow in an NCP connection is one-directional, meaning that applications wanting bidirectional communication have to use a pair of connections, whereas TCP allows communication in either direction over the same connection.
A 1983 TCP/IPv4 stack probably could successfully communicate with a 2019 TCP/IPv4 stack, although changes in TCP congestion algorithms, MTU discovery, etc would likely cause significant performance issues over long-distance links. TCP/IP and NCP are completely incompatible protocols so TCP/IP-only host could not communicate with an NCP-only host at all.