ATM

An automated teller machine (ATM), commonly called a cash point in UK English after the trademark of the same name, is a computerized telecommunications device that provides the clients of a financial institution with access to financial transactions in a public space without the need for a cashier, human clerk or bank teller. ATMs are known by various other names including automatic banking machine, cash machine, and various regional variants derived from trademarks on ATM systems held by particular banks.
Most ATMs are connected to interbank networks, enabling people to withdraw and deposit money from machines not belonging to the bank where they have their account or in the country where their accounts are held (enabling cash withdrawals in local currency). Some examples of interbank networks include PULSE, PLUS, Cirrus, Interac, Interswitch, STAR, and LINK.
ATMs rely on authorization of a financial transaction by the card issuer or other authorizing institution via the communications network. This is often performed through an ISO 8583 messaging system.

There are no hard international or government-compiled numbers totaling the complete number of ATMs in use worldwide. Estimates developed by ATMIA place the number of ATMs in use currently at over 1.8 million.
India claims to have the world's highest installed ATM at Nathu La Pass, India installed by the Union Bank of India at 4310 meters, there are higher ATMs installed in Nagchu County, Tibet at 4500 meters by Agricultural Bank of China.
Security, as it relates to ATMs, has several dimensions. ATMs also provide a practical demonstration of a number of security systems and concepts operating together and how various security concerns are dealt with.