Whose framing this is

The market-window idea — that a company's fate turns on whether it arrived while a market was open — is James L. Pelkey's, from the interviews behind A History of Computer Communications, 1968–1988. It is attributed by name here and in the two companion articles because it is his analysis, not a general observation.

The trigger was accumulation, not permission

The first window opened because a regulator allowed something. This one opened because organisations had spent a decade buying computers and had ended up with a building full of machines that could not reach each other.

There is no ruling to date it to. The need built up until it was worth solving, which is why 1979 is approximate where 1968 was exact. What can be dated is when companies started being founded to answer it, and they cluster.

Two answers to the same question

The interesting thing about this window is that it opened with a genuine contest, and both sides were reasonable.

The data PBX answered it as a telephone engineer would: a switch in the middle, connecting a terminal to a computer port on demand, exactly as a PBX connects a telephone to a line. It was well understood, it used known components, and it fit the way buildings were already wired.

The local area network answered it as a computer engineer would: give everything an address, put it on a shared medium, and let the endpoints sort out who talks. No central switch decides anything.

The second answer won, and the reason is worth teaching. Not because circuit switching was wrong, but because the LAN's cost per attached device fell as the number of devices grew, and the 's did not. A switch with more ports is a bigger switch. A shared network with more stations is the same network.

What the window produced

and the contest around it — , ARCNET, and a long tail of proprietary schemes that a building could be wired for and later regret. Network interface cards as a product category. The first companies whose entire business was connecting computers to each other rather than to a terminal.

And the data PBX vendors, who were not fools and who built substantial businesses that then had nowhere to go. This is the clearest case in the period of a product that was correct and was overtaken, which is a different thing from a product that was wrong.

Why it closed

By 1982 the question had an answer, and the answer had a supply chain. A company founded in 1984 to build a better local area network was not entering an open market; it was attacking incumbents with established channels.

What it did leave behind was a new problem, and the new problem opened the next window: organisations now had several local area networks and no way to join them.

What the numbers show about both answers

Local area networking was a $63 million market in 1982, the year the window closed. By 1988 it was $2.82 billion — a market roughly forty-five times larger, built almost entirely by companies that had already been founded.

The data PBX series is the other half of the story, and it is short. It climbed to about $143 million in 1985 and then fell — $86 million in 1986, $80 million by 1988 — while the LAN line went up by a factor of five over the same three years.

That is what "correct and overtaken" looks like as a number. Nothing collapsed; a market simply stopped growing while the thing beside it did not.

Figures from Pelkey, Appendix A.1, Product Revenues 1970-1988.