x86-based 64-bit systems sometimes lack equivalents of software that is written for 32-bit architectures. The most severe problem in Microsoft Windows is incompatible device drivers. Most 32-bit application software can run on a 64-bit operating system in a compatibility mode, also known as an emulation mode, e.g. Microsoft WoW64 Technology for IA-64 and AMD64. The 64-bit Windows Native Mode[23] driver environment runs atop 64-bit NTDLL.DLL, which cannot call 32-bit Win32 subsystem code (often devices whose actual hardware function is emulated in user mode software, like Winprinters). Because 64-bit drivers for most devices were not available until early 2007 (Vista x64), using a 64-bit version of Windows was considered a challenge. However, the trend has since moved towards 64-bit computing, particularly as memory prices dropped and the use of more than 4 GB of RAM increased. Most manufacturers started to provide both 32-bit and 64-bit drivers for new devices, so unavailability of 64-bit drivers ceased to be a problem. 64-bit drivers were not provided for many older devices, which could consequently not be used in 64-bit systems.