In payment systems, the section inside an ATM where cash is physically stored is called the tower.
Inside the tower:
- Compartments holding 20, 50, and 100 TL banknotes (the denominations assigned to each compartment vary from bank to bank)
- A mix cassette (reject unit) that holds cash deposited outside the ATM's designated denominations. For example, based on the above, any banknotes other than 20, 50, or 100 TL (such as 10 or 200 TL) go into the mix cassette.
Does every ATM have only one tower?
While a single tower is most common, there are also dual-tower ATM models. Dual-tower ATM models are placed in locations with very high cash flow. This way, the frequency of cash replenishment for the ATM is cut in half.
Security of the tower
The tower is the safe compartment inside the ATM and is built to withstand physical attacks. Safe compartments are classified according to certified security levels. In higher-risk locations, safes with higher security levels are preferred.
Additional security measures
In addition to the safe itself, various other security measures are used to protect the tower:
- Multi-stage lock systems on the safe door
- Systems that dye the banknotes, rendering them unusable, if forced entry into the safe is attempted
- Door-opening and vibration sensors along with alarm systems
Managing the cassettes
During cash replenishment, the cassettes inside the tower are typically replaced with full ones. The amount of cash in each cassette is recorded in the ATM's software. The ATM logs how many banknotes were dispensed from which cassette for every withdrawal. At the end of the day, these records are reconciled against the cash remaining in the cassettes.
Denomination selection
Which denomination is assigned to which cassette is determined by the withdrawal habits at the ATM's location. For example, locations with frequent high-value withdrawals are weighted toward larger denominations, while locations with frequent small withdrawals are weighted toward smaller denominations.
