ArcaOS includes several “compatibility subsystems” which enable the execution of ported or native applications. Currently, these subsystems include:
Win32 API Extensions (Odin32)
Odin32 is a compatibility API used by some 32-bit applications ported from Windows. Some native Windows applications are able to run unmodified utilizing this subsystem. Others must have been ported to OS/2 from Windows, and utilize various Odin32 libraries to satisfy runtime requirements.
OpenJDK is a Java 6 runtime environment. Java applications run natively under OpenJDK 6 in ArcaOS.
Qt4 is a graphical user interface library used by some popular applications. These applications must be compiled for use under OS/2. Many are packaged as RPMs and available for installation using Arca Noae Package Manager.
Common Unix Printing System
CUPS is a framework used to support many modern printers. The native OS/2 print subsystem passes jobs to the CUPS queue for servicing. This allows even older, non-CUPS-aware applications to utilize this framework and leverage the availability of newer printer models. CUPS itself is generally managed through a web browser interface.
ArcaOS includes OS/2’s full virtual DOS machine (VDM) support. Note that minimal VDM support, without support files or configuration tools, is always installed with ArcaOS to satisfy dependencies of some OS/2 components. The OS/2 VDM is a fully-compatible IBM PC-DOS 6 workalike, with the ability to load DOS device drivers into the DOS high memory area, providing an unprecedented amount of memory for the DOS application running in the VDM. Further, ArcaOS has the ability to run multiple VDMs concurrently, each in a separate memory space. Both EMS and XMS memory is supported for applications able to use either or both of these technologies.
This is OS/2’s virtualized Windows 3.x subsystem. From the Windows Program Manager to individual 16-bit Windows applications, the ArcaOS Win-OS/2 environment provides windowed (on the ArcaOS desktop) and full screen sessions. Win-OS/2 support requires DOS support, and like the DOS environment, Win-OS/2 sessions are highly configurable in terms of memory and other system resources.
Unix Compatibility (kLIBC)
The Unix Compatibility Subsystem in ArcaOS is provided through a LIBC environment called kLIBC. Linux and Unix applications compiled to run on OS/2 in this environment are built from the same source code as their Linux and Unix counterparts, usually with little to no modification. This environment provides other Unix-like functionality, as well, including ported Unix command shells (sh, ash, bash, dash, ksh, etc.) and symbolic link (symlink) support. To learn more about the kLIBC environment, see this sub-wiki.