Cotation Assistée en Continu

~ the goodbye ~

The CAC in CAC 40 is a dead computer. Everyone who has ever glanced at a French market number has read the acronym without being told that it stands for Cotation Assistée en Continu, continuous assisted quotation, and that it was the name of a specific piece of software the Paris Bourse ran for about nine years. The index is still quoted every weekday. The machine it was named after was switched off in 1995.

The design was Canadian. The Bourse bought a license in the early 1980s from the Toronto Stock Exchange, whose CATS had been automating price discovery since 1977, and ran the Canadian design under a French name. It arrived in 1986 on the illiquid end of the list, where the shares nobody wanted to stand around quoting all day lived. By 1989 it was carrying every listed equity in Paris.

What that meant in practice was the end of the criée. Trading in Paris had been done by shouting in a pit at the Palais Brongniart since the building was finished, and the pit did not survive the arrival of a central order book that matched orders in milliseconds for free. Fabian Muniesa wrote the sociology of that transition in 2005, under a title that translates roughly as containing the market, which is a better description of what the software did than anything the exchange published at the time.

I watched the CAC 40 the way most people outside France do, as a row on a finance page next to the DAX and the FTSE. The number meant something to me in the way an exchange rate means something. I did not learn until this year that the letters were a product name, and that the product was a Toronto mainframe program nobody in Paris had written.

~ the chronicle ~

~ the coincidence in the name ~

There is a second reading of those three letters that is too neat to be deliberate and seems to have been exactly that. CAC also fits the Compagnie des Agents de Change, the old Parisian stockbrokers' association whose members held the legal monopoly on executing trades. So the acronym for the system that automated them away also spelled out the name of the guild it replaced. The index launched in 1988, between the first rollout and the full one, and inherited the letters while both meanings were still live.

~ how it actually ended ~

In 1995 the Société des Bourses Françaises finished a successor of its own and called it NSC, Nouveau Système de Cotation. CAC came off and NSC went on. No French source I can reach puts a day on the cutover, which fits the pattern for this kind of death: a matching engine is replaced stock by stock over weeks, and the last batch moves across on an ordinary Tuesday that nobody writes down.

NSC turned out to matter more than the thing it replaced. When Paris merged with Amsterdam and Brussels into Euronext in 2000, it was the French engine that became the shared platform underneath, and the Paris Bourse itself became Euronext Paris. The software Toronto sold to Paris in the early 1980s came back to Toronto as a license around 1997, by way of a rewrite that had dropped the Canadian name.

~ what got buried with it ~

The Palais Brongniart is an events venue now. You can rent the room where the pit was. The exchange that once required a licensed agent de change standing in it to turn an order into a trade is a line of code in a data center somewhere outside the city, and the only surviving trace of the machine that did the converting is four letters on a ticker that no longer expand to anything anybody says out loud.

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