1. Short for Asynchronous Transfer Mode, ATM when referring to computers is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical environment using digital signal technology. ATM is capable of transmitting at speeds of 155 or 622 MBps and faster.
2. Short of Automated Teller Machine, an ATM dispenses money from a persons account at banks. The first U.S. ATM went into service at 9:00am on September 2, 1969. The picture shows an example of what a typical ATM may looks like today.
3. Shorthand for At The Moment, ATM is commonly used in chat based communications. Below are some examples of how this could be used in chat.
I'm busy ATM.
ATM I'm watching the Simpson's.