Editing 64-bit computing (section)

=== Software availability ===
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 driver]]s for obsolete hardware. Most 32-bit application software can run on a 64-bit operating system in a [[compatibility mode]], also termed an [[emulator|emulation]] mode, e.g., Microsoft [[WoW64]] Technology for IA-64 and AMD64. The 64-bit Windows Native Mode<ref>{{cite web |url=https://technet.microsoft.com/en-us/sysinternals/bb897447.aspx |title=Inside Native Applications |publisher=Technet.microsoft.com |date=2006-11-01 |access-date=2010-11-19 |archive-url= https://web.archive.org/web/20101023130328/http://technet.microsoft.com/en-us/sysinternals/bb897447.aspx |archive-date= 23 October 2010 |url-status= live}}</ref> driver environment runs atop 64-bit {{Mono|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&nbsp;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.

Driver compatibility was less of a problem with open-source drivers, as 32-bit ones could be modified for 64-bit use. Support for hardware made before early 2007, was problematic for open-source platforms,{{Citation needed|date=February 2013}} due to the relatively small number of users.

64-bit versions of Windows cannot run [[16-bit#16-bit application|16-bit software]]. However, most 32-bit applications will work well. 64-bit users are forced to install a [[virtual machine]] of a 16- or 32-bit operating system to run 16-bit applications or use one of the alternatives for [[NTVDM]].<ref>{{cite web|url=https://www.pcworld.com/article/2045345/run-an-old-program-on-a-new-pc.html|title=Run an old program on a new PC|author=Lincoln Spector|date=August 12, 2013}}</ref>

[[Mac OS X Tiger|Mac OS X 10.4]] "Tiger" and [[Mac OS X Leopard|Mac OS X 10.5]] "Leopard" had only a 32-bit kernel, but they can run 64-bit user-mode code on 64-bit processors. [[Mac OS X Snow Leopard|Mac OS X 10.6]] "Snow Leopard" had both 32- and 64-bit kernels, and, on most Macs, used the 32-bit kernel even on 64-bit processors. This allowed those Macs to support 64-bit processes while still supporting 32-bit device drivers; although not 64-bit drivers and performance advantages that can come with them. [[Mac OS X Lion|Mac OS X 10.7]] "Lion" ran with a 64-bit kernel on more Macs, and [[OS X Mountain Lion|OS X 10.8]] "Mountain Lion" and later [[macOS]] releases only have a 64-bit kernel. On systems with 64-bit processors, both the 32- and 64-bit macOS kernels can run 32-bit user-mode code, and all versions of macOS up to macOS Mojave (10.14) include 32-bit versions of libraries that 32-bit applications would use, so 32-bit user-mode software for macOS will run on those systems. The 32-bit versions of libraries have been removed by Apple in macOS Catalina (10.15).

[[Linux]] and most other [[Unix-like]] operating systems, and the [[C (programming language)|C]] and [[C++]] [[toolchain]]s for them, have supported 64-bit processors for many years. Many applications and libraries for those platforms are [[open-source software]], written in C and C++, so that if they are 64-bit-safe, they can be compiled into 64-bit versions. This source-based distribution model, with an emphasis on frequent releases, makes availability of application software for those operating systems less of an issue.