Diebold has attacked the reliability of NCR’s new single-slot, mixed-media ATM technology that can accept intermingled cash and checks. But early returns suggest NCR’s automated teller machines work well enough to satisfy Wells Fargo & Co. and BMO.

Diebold, of Canton, Ohio, is taking aim at the reliability of single-slot and mixed-media ATMs. Diebold says it does not offer single-slot ATMs because the machines hinder availability in case of a jam, it says, and that two slots are the most reliable way to process deposits.

“With two deposit slots operating simultaneously, one for cash deposits and the other for check deposits, in the unlikely event of a jam at the cash slot, dual deposit functionality could offer continuous availability because the check slot would likely remain operational, avoiding a complete shut-down at the ATM,” Diebold said in a statement.

The battle over single- versus dual-slot strikes at the heart of the battle between ATM manufacturers.

A lot is riding on NCR’s technology, which it refers to as “scalable deposit module” and which it is positioning as one of its major innovations.

NCR’s ATMs are designed to be easier and faster to use: a deposit of five bills and two checks would take less than 60 seconds, on average. “It’s faster and a much better user experience,” says Bob Tramontano, a vice president at NCR.

Single-slot “single-media” ATMs and more general envelope-free ATM deposits have existed for a couple of years. The wrinkle for NCR is mixed media, or the ability of the user to input paper money and checks in any order, even intermingled. Earlier generations of single-slot ATMs require the user to enter which type of paper cash or check is being deposited and manually separate the two.

“Usability will always win. We haven’t seen any issues with [single-slot] ATMs,” says David Albertazzi, a senior analyst at Aite. Wells Fargo has beta tested NCR’s latest generation of single-slot ATMs and has done a larger rollout, Albertazzi says. “As we’ve learned with online and mobile, usability and the user experience will really drive the winning technology or will help determine which technology will win.”

NCR just signed a deal to replace “a large portion” of BMO Harris Bank’s 1,300 ATMs, which will replace older machines in the bank’s Chicago area footprint.

BMO, which made NCR its exclusive provider for BMO Harris ATMs, did not release its list of previous ATM suppliers or have an executive available for comment.

Wells Fargo, which has installed about 2,600 of NCR’s mixed-media ATMs, says the machines have performed as well as dual-slot ATMs or non-mixed-media single-slot ATMs.

“We don’t see a huge difference between single-slot ATMs and dual-slot ATMs in terms of jams or other risks,” says Alicia Moore head of ATM banking at Wells Fargo. Including non-mixed-media machines, the bank has about 7,200 total single-slot ATMs, some manufactured by Wincor Nixdorf, another ATM provider.

Wells Fargo also has deployed several hundred dual-slot ATMs manufactured by Diebold.

Wells Fargo didn’t release usage data for various types of ATMs, but Moore says the single-slot macines are “slightly more intuitive,” and that the bank doesn’t mix different ATMs in the same market. She said the bank’s major recent ATM project — extending the daily cutoff time for deposits to be included in that days’ records — is being extended to all ATMs. Other early adopters of SDM are JPMorgan Chase & Co. and Redwood Credit Union, which deployed some of the machines near San Francisco.

In a statement addressing Diebold’s criticism, NCR said that “both NCR engineering tests and customer trials have demonstrated that the scalable deposit module, with single-slot deposit, performs as well or more reliably than other solutions in the market.”

NCR says its method of separating bills from checks, which it calls dynamic deskew, is designed to remove imperfections in scanning, mostly from wrinkles, and reduces jams.

“Checks are stiff, cash is more like cloth; the machine straightens out the documents and applies pressure to determine which one it is,” Tramontano says. The images are captured and given back to the user for verification and correction, he says.

The technology was designed at the Duluth, Ga., company’s research and development facility in Ontario.

Among the targeted users for the ATMs are small-business operators or contractors such as cab drivers.