Can ATM work without Internet?

Does ATM need Internet? 

Assuming you mean an Automated Teller Machine, no, they do not rely on the Internet. Instead, they use the bank's own private network. Frequently, that's not even an IP network.

How ATM works as a system?

ATM (Automatic Teller Machine) is a banking terminal that accepts deposits and dispenses cash. ATMs are activated by inserting cash (in cases of ATM Depositing) or debit /credit card that contain the user's account number and PIN on a magnetic stripe (for cash withdrawals). The ATM is made of the CPU (microprocessor). 

How does an ATM work internally?

Once an user inserts his/ her debit card or credit into the Automated Teller Machine, it scans and encodes the data given on the magnetic stripe on the back of the card. Soon after this, the cash dispenser of the ATM gives out the required amount of cash to the user from cash cartridges located in its internal vault.

Can an ATM machine be hacked?

A staggering 85 percent of ATM cash machines can be hacked and tricked into dispensing free cash within just 20 minutes, a new report warns. Bank security experts Positive Technologies described in a report this week a number of successful attempts to gain access to an ATMs operating system.