The Plumbing

Every working day, a computer system most Britons have never heard of moves roughly £360 billion between UK banks. It is called CHAPS. It turns over something close to the country's annual GDP about every week. Fedwire, its American cousin, moves around $4 trillion a day. Nothing physical travels. No van, no vault, no queue. Money, for almost every purpose that matters, is entries migrating between balance sheets inside systems with names nobody learns. The high-street branch with the marble columns is a stage set. The machine is the plumbing underneath. If you want to know where the next crisis starts, stop watching the lobby.

Start with the hierarchy. Your money is a bank deposit, an IOU from Barclays. Barclays' money is reserves, an IOU from the Bank of England. When you pay someone who banks elsewhere, your bank must settle with theirs in reserves, across CHAPS in the UK, Fedwire in the US, TARGET2 in the eurozone. These are real-time gross settlement systems: finality, one payment at a time, in central bank money. Everything above that layer is promises. The layer matters because it reveals what "money in the bank" actually is: a claim on an institution's ability to obtain reserves when asked. Most days, nobody asks all at once. The entire architecture is a bet that most days continue.

Now cross a border and watch the hierarchy blur. A bank in Singapore takes dollar deposits and makes dollar loans without touching the United States, settling through correspondent accounts at banks that ultimately hold Fed reserves. These offshore dollars, eurodollars, are created outside the Fed's regulatory reach and largely beyond its sight. The BIS has estimated that dollar obligations hidden in FX swaps (functionally debt, booked off balance sheet) exceed $80 trillion. The Fed does not control the world's dollar system; it discovers the size of it whenever the system breaks and swap lines must be flung open, as in 2008 and March 2020. "The" dollar is a family of claims of varying distance from the real thing.

The overnight heart of all of it is repo: sell a bond today, agree to buy it back tomorrow at a slightly higher price. It is a collateralised loan in everything but name. Trillions roll over every night, funding dealers, hedge funds, and banks against the safest collateral in existence, government bonds. But collateral gets reused. Under rehypothecation, the Treasury you pledged to me becomes the Treasury I pledge to someone else, the same bond propping up a chain of borrowings. Manmohan Singh's IMF work found each piece of prime collateral supporting multiple transactions at once. The money market is, on honest inspection, a collateral market. Its base metal is not cash but the government bond, which is why module 6's gilt story matters so much.

So where does fragility live? Not at the counter. Film-set bank runs (queues, cashiers, panic) are the rare, retail tail of the phenomenon. Real runs happen at 7am between institutions: a haircut rises, a counterparty declines to roll your repo, a collateral chain shortens, and funding that existed yesterday is gone system-wide by lunch. There is no single system. There is a stack of balance sheets (the Fed, the Bank of England, eurodollar banks, dealers, clearing houses, funds) with no master switch and no single operator. That is not a conspiracy; it is worse. It is an unsupervised machine that everyone assumes someone else is steering. Module 6 shows what happens when a pipe bursts.