Tzvetan Mikov (tmikov@gmail.com) on 5/8/06 wrote:

...

the article describes NT's kernel as a "hybrid kernel" sharing architectural
>concepts or mechanisms with microkernel designs such as "message passing" and "migration
>of "non-essential" code into user space". This strikes me as rubbish for two reasons:
>- In NT messages (IRPs) are used for implementing asynchronous execution, which
>is essentially an implementation detail and has nothing to do with microkernels.
>As a matter of fact IRPs are so fragile, that in a sense they achieve an effect opposite to a microkernel.
>- All essential subsystems in NT are implemented in the kernel - filesystems, usb,
>networking, etc. Of course there are components in user space which are considered
>part of the OS (what isn't in Windows?), but such components are implented in user space in all OS-es.

Just dropped by to see what the reaction to SGI's unfortunate predicament was, and happened upon your post.

Understanding NT's characterization as micro-kernel-related probably requires knowing something about how it evolved. In the beginning, it had (at least) three distinct personalities: Windows, POSIX, and OS/2 (IIRC). Each personality (and much of the graphics system as well) was implemented as a user-space service which applications needing it accessed via message passing (IRPs are kernel constructs which have nothing to do with the message-passing facilities being referred to).

Graphics support got inhaled into the kernel proper after performance became an issue. POSIX and OS/2 support withered and the Windows 'personality' became little more than a set of user-mode library stub interfaces rather than a separate protected user-mode server.

Even in the beginning NT's kernel contained considerably more than a classic micro kernel, but it at least had *some* resemblance to one.

- bill