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 for obsolete hardware. Most 32-bit application software can run on a 64-bit operating system in a compatibility mode, also termed an emulation mode, e.g., Microsoft WoW64 Technology for IA-64 and AMD64. The 64-bit Windows Native Mode 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 unavailable until early 2007 (Vista x64), using a 64-bit version of Windows was considered a challenge. However, the trend has since moved toward 64-bit computing, more so 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.