Description Hybrid kernel

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the windows nt design includes many of same objectives mach, archetypal microkernel system, 1 of important being structure collection of modules communicate via well-known interfaces, small microkernel limited core functions such first-level interrupt handling, thread scheduling , synchronization primitives. allows possibility of using either direct procedure calls or interprocess communication (ipc) communicate between modules, , hence potential location of modules in different address spaces (for example in either kernel space or server processes). other design goals shared mach included support diverse architectures, kernel abstractions general enough allow multiple operating system personalities implemented on top of , object-oriented organisation.


the reason nt not microkernel system of subsystems providing system services, including entire executive, run in kernel mode, in same address space microkernel itself, rather in user-mode server processes, case microkernel design. attribute nt shares versions of mach, commercial systems based on mach, , stems superior performance offered using direct procedure calls in single memory space, rather ipc, communication amongst subsystems. user-mode subsystems on nt include 1 or more emulation subsystems, each of provides operating system personality applications, session manager subsystem (smss.exe), starts emulation subsystems during system startup , local security authority subsystem service (lsass.exe), enforces security on system. subsystems not written particular os personality, rather native nt api (or native api).


the primary operating system personality on windows windows api, present. emulation subsystem implements windows personality called client/server runtime subsystem (csrss.exe). on versions of nt prior 4.0, subsystem process contained window manager, graphics device interface , graphics device drivers. performance reasons, however, in version 4.0 , later, these modules (which implemented in user mode on monolithic systems, designed without internal graphics support) run kernel-mode subsystem.


as of 2007, 1 other operating system personality, unix, offered optionally installed system component on versions of windows vista , windows server 2003 r2. associated subsystem process subsystem unix-based applications (psxss.exe), formerly part of windows add-on called windows services unix. os/2 subsystem (os2ss.exe) supported in older versions of windows nt, limited posix subsystem (psxss.exe). posix subsystem supplanted unix subsystem, hence identical executable name.


in august 2016, microsoft unveiled latest windows subsystem called linux subsystem windows (lxss.exe). subsystem, available on 64-bit windows 10 version 1607 (anniversary update, codenamed redstone), runs slimmed down version of ubuntu 14.04 lts natively within operating system without emulation achieve this. marketed bash on windows , because ran bash, popular command line interface used on many linux distributions , macos, , allows binaries compiled amd64 run unmodified within subsystem. intended developers run tools on windows without having emulate them, , requires developer mode enabled in windows settings. designed run command-line applications, although reddit user has discovered way run gui applications or entire desktop environment it. applications strictly rely on linux kernel not able run because not include linux kernel.


applications run on nt written 1 of os personalities (usually windows api), , not native nt api documentation not publicly available (with exception of routines used in device driver development). os personality implemented via set of user-mode dlls (see dynamic-link library), mapped application processes address spaces required, emulation subsystem server process (as described previously). applications access system services calling os personality dlls mapped address spaces, in turn call nt run-time library (ntdll.dll), mapped process address space. nt run-time library services these requests trapping kernel mode either call kernel-mode executive routines or make local procedure calls (lpcs) appropriate user-mode subsystem server processes, in turn use nt api communicate application processes, kernel-mode subsystems , each other.



the xnu kernel








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