ATM: Some Peculiarities

None of us are surprised by ATMs anymore. Even older generations have gradually gotten used to these devices and can manage to withdraw their pensions. However, beyond everything else, an ATM is an extremely fascinating thing from both a technical and organizational standpoint. Even employees of banking institutions (including those working with payment cards) don't always understand the nuances of how they work. In a previous life, I spent quite a few years dealing with payment cards and servicing ATMs. I've had to thaw one out with a hair dryer and pick out, piece by piece, a mouse that got stuck inside hugging the banknotes. I even burned down one of my assigned ATMs. Twice. So I'll share some technical details about how ATMs work that I find interesting.

Unfortunately, most of my work in this area fell during a period when even a 0.3MP camera phone was quite a luxury — so I have virtually no photos of my own.

40 Banknotes

An ATM dispenses no more than 40 banknotes at a time. This is due to the mechanical feed mechanism. So when you're withdrawing money from an ATM and the screen shows "Available denominations: 50, 200" — if you need to withdraw a large sum, you can immediately calculate the maximum amount the ATM can give you. If you try to request more than 40 banknotes, the ATM will think about it and refuse. And you'll be left wondering why.

30 Seconds

The response interval for each operation, after a customer action, must be no more than 30 seconds. This is a requirement of international payment systems. The customer inserts their card — the ATM can ponder for 29 seconds before responding. Customer selects a menu item — again, it can think it over. And so on. In the old days, when communication links weren't great, this was a crucial detail. Nowadays, things are a bit easier.

The White Supervisor Card

Yes — exactly that kind. It comes with every ATM. Just like regular cards, it also has a PIN code and an expiration date.

It may also work with other ATMs. I can't share the full details here — I once accidentally used a card from one ATM on another one of my ATMs, and it worked. Whether that's by design or it works within the same processing center — I don't know. I should have probably gone to an ATM at another bank to test it. But I didn't feel like getting up.

The card is required for performing cash collection/auditing of the ATM and certain technical functions — you can dispense as many banknotes from the cassettes as you want, open and close the dispensing slot, flash the indicators and displays, and so on. Enter the wrong code three times and the card is blocked until the next day.

The Brains

Beyond the "system unit" (let's call it that), the ATM's keyboard, card reader module, and display each have their own brains. You can't just take parts from one ATM and plug them into another. When connecting new devices, you need to enter cryptographic 3DES keys. These keys are written to the connected devices and allow them to work with that specific ATM. The keys come in 2 envelopes (like PIN code envelopes for regular cards) containing a sequence of digits. Two people each receive one envelope and enter the keys.

Cash Cassettes

An ATM typically has 4-6 cash cassettes. Each cassette holds approximately 2,500 banknotes. Each cassette is configured for a specific denomination. So even if cassettes get swapped during cash collection, the chip in the cassette won't allow money to be dispensed from the wrong slot. The flip side of the coin — if you load 50-dollar bills into a cassette meant for 20s, then (with a fair bit of luck, if the physical characteristics of the bills are similar enough) the ATM will start dispensing bills of a higher denomination. The ATM operator and the head cashier can start opening their wallets to cover the shortage. That's happened too...

The Reject Cassette

Stuck-together banknotes, banknotes that the ATM doesn't like for one reason or another, and money that you didn't pick up from the dispensing slot — all get tossed into the reject cassette. It's about half the size of a standard cassette.

ATMs Get Cold

Outdoor ATMs have 100% moisture protection. However, they're sensitive to cold. Early ATM models didn't have the "Russian Winter" heating element package, so when the outside temperature dropped below minus 10-15 degrees Celsius, ATMs would start acting up. This was especially relevant when the ATM was placed in a storefront window, with its front (inner) side actually pressed against the glass and freezing. The ATM might not turn on at all, because diagnostics would complain and demand warmth for the ATM (pro tip for the home: to get an ATM to start up in this situation, you need to blow a hair dryer on the temperature sensor). The cash dispensing mechanism might not work, along with other delights.

Confiscated Cards

People leave their cards in ATMs. Sometimes accidentally, sometimes after entering the wrong PIN three times, and sometimes — you're withdrawing money, power goes out, the ATM shuts down, and that's basically it... then you have a choice: stand there as long as you can and wait for your card (which, characteristically, will pop out when power comes back — and if not you, then someone else will grab it, if they're quick enough) or go home, and the ATM will eventually take the card for itself. Often, nobody came back for their cards. Over several years, we accumulated quite a collection of cards from various banks, including foreign ones.

Old ATMs

Between 2002 and 2004, quite a few used ATMs were brought to Ukraine from Europe and the US. Here they'd be fixed up, serviced, and sold to banks. They were approximately 8-12 times cheaper ($5,000-8,000) than new modern ATMs ($80,000-110,000). They worked, frankly speaking, terribly, but since the card business was just getting started and revenues were low (ATMs are installed not for your own customers but for other banks' customers), not all banks could afford new ATMs in the volumes needed. So they installed whatever was cheaper. These ATMs had old CRT monitors with the burned-in logos of European banks (previous owners). The canonical operating system for ATMs of that era was OS/2.

The ATM Safe

It stores the cash cassettes and the reject cassette. It's typically a safe with a key and a combination dial. The combination needs to be changed regularly. It's very unpleasant when, after changing the combination and closing the door, you realize the code doesn't work and the safe no longer opens.

Receipts

The printers used are dot-matrix (older ATM models) and thermal printers. Receipt paper comes in rolls. Usually 2,000-5,000 receipts per roll. The problem with dot-matrix printers is that cartridges are hard to find. The problem with thermal printers is that when it's cold and you're warming up the ATM with a hair dryer — if you accidentally hit the receipt paper with the air stream, you'll end up with a completely black ribbon.

The Mouse

Winter. The ATM was located in a bank branch, but in a remote empty room, facing outward through a window. Cold. A mouse found a way in (ATMs have plenty of openings for cable routing) and climbed inside to warm up. The cash dispensing mechanism ended up crushing it thoroughly. I ended up there because the ATM had stopped working and bloody banknotes were sticking out of the reject cassette. I had to disassemble half the ATM to extract what was left of the mouse and three torn banknotes. It died a hero's death — but it died with money.

If this article was interesting, I can continue the topic of banking hardware.

Update 2014/03/21: Continuation: Card Games