During the Leeds trial, the Visa Cash Merchant Card (VCMC), also called a PSAM (Purchase Secure Application Module) card were used in each merchant's point of sale (POS) terminal that accepted Visa Cash cards. The VCMC was used to authenticate each and every Visa Cash transaction with that particular POS terminal was a real transaction and not fraudulent. The VCMC used a very sophisticated technology to cryptographically check the consumer's Visa Cash card. It verified that money had been removed from the consumer's Visa Cash card and that the card was valid.
The VCMC authenticated purchase transactions “offline”, that is, not connected to the main bank computer all the time. Typically once a day the POS terminal automatically called a financial institution’s collection point (the main bank computer) to transfer that day's transactions and credit the merchant’s bank account. It was vital (for obvious reasons) to make sure that these purchase transactions were valid and not altered for larger amounts or forged. The VCMC also provided a way for the merchant to be paid if for any reason the merchant’s POS terminal lost any or all transactions. The merchant would always be paid on the total provided by the VCMC and thus provided assurance to the merchants that they would be paid regardless of any problems in their POS terminals.
Additionally, there were other even more sophisticated security features used to prevent fraud with disposable Visa Cash cards, in order to prevent the manufacture of counterfeit Visa Cash cards. The above VCMC is a specific version of the VCMC that supported these more technically advanced security features. These advanced security features both on the VCMC and Visa Cash cards proved so secure that there was never any fraud from counterfeit cards nor any breaches into the chip to add value to the card during the course of the Visa Cash card programs, worldwide.
Note the area of the VCMC card where the chip could be punched out. This area of the card was the SIM, which stands for “Subscriber's Identity Module”. SIM chips are now commonly used in cell phones today, but in mid-1990’s was at the leading edge of technology. Visa had the VCMC’s manufactured so that the SIM could be easily punched out, so that a merchant’s POS terminal didn't need to provide room for an entire card (although most probably did).
Lastly, these VCMC’s were actually the property of Visa and its financial institutions and were not for sale to the general public and available only to the specific merchant(s) for use in participating in the Visa Cash program(s).
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ATM's. 
