Millions of people use an ATM every day, and as long as it provides the money they need, they probably don’t think much about how it works. But if you’ve ever wondered how much money is held in an ATM or why they can only put out denominations of $10 or $20, this article will take a look into the inner workings of ATM machines.

Accessing The Network

Inside every ATM is a computer that really isn’t that much different than any personal computer, but with the basic function of connecting you to the bank ATM network and accessing your account information. Many ATMs actually run on common Microsoft software, although some older and international ATMs run on operating systems such as Linux or MS DOS.

Two-Layer Security

Because an ATM has access to your digital banking information through the card reader and also provides physical cash, two layers of security are necessary. The first is the card reader, which is similar to a credit card reader you would use for a point-of-sale transaction. The card reader is equipped with a high level cryptoprocessor that safeguards the information you input. This card reader will also hold the card if it is left for too long or too many incorrect PIN input attempts are made.

The second layer of security is physical, and essentially consists of a safe built into the machine. Inside this safe are several cash cartridges, which hold the bills to be dispensed. These are most often filled with $20 bills, but can also be filled with any other denomination depending on the amount of cash going through the ATM and customers’ bill size preference. As a theft deterrent, many ATMs have dye or smoke canisters in these cartridges that are designed to render the bills useless if people attempt to force access to the money.

Getting You Your Money

The end goal of any ATM, of course, is to get you cash in hand, and to do this there are a number of mechanisms that choose bills and dispense them. There are also readers that determine if the right number of bills has been selected and whether the customer has taken the money. If too many bills were picked, or if the money is not extracted in a certain amount of time, the machine will set aside the money in a “purge” bin. Finally, there is a printer that prints out receipts and statements.

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