Most of the computers are being delivered with the 64-bit versions of Windows operating systems (Windows 7 and Windows Server 2008) and some confusion has developed around implementation of TWAIN-based scanners. The TWAIN Working Group has released the 2.0 spec for TWAIN and a new 64-Bit Data Source Manager a couple of years ago. However, most of the currently available scanners do not yet come with true 64-Bit TWAIN drivers.
The situation is even more confusing when you realize that in the 64-Bit version of Windows, you can run 32-Bit applications, and use 32-Bit drivers. But the 32-Bit applications will only use the 32-Bit drivers, and the 64-Bit drivers will only work with true 64-Bit applications.
For example, if you install a scanner on a 64-bit OS, which only installs a 32-bit driver, then only the 32-bit applications will recognize the scanner on the 64-bit OS.
Some scanner suppliers are advertising drivers as 32/64-Bit compatible. But in most cases it only means that the drivers will work in both 32-Bit and 64-Bit versions of Windows. The user can use the 32-Bit drivers in 64-Bit Windows, but only with 32-Bit applications.