Skynet

In the first two films, Skynet is a colossal piece of hardware, a single unit which contains an artificial intelligence designed to run the US nuclear weapons system, a doomsday computer that becomes aware and destroys humanity. […] It was only through some very fancy footwork that Terminator 2: Judgment Day managed to make it remotely plausible that Skynet had sent a second machine to a later date. Since Skynet is presumably aware of its own origins, this makes the first film marginally less plausible.