[TUHS] Happy birthday, Ken Thompson!

Paul Winalski paul.winalski at gmail.com
Mon Feb 4 12:03:04 AEST 2019

On 2/3/19, Clem Cole <clemc at ccc.com> wrote:
> IBM CP-DOS -> OS/2 --\
>                                        \
>                                          ---> NT OS-2 -> NT/WIN .......
>  Today's Windows
> CMU Mach --\                  /
>                       ---> Mica -/
> DEC VMS   --/

I think that bottom part should read:

CMU Mach --\
                     ---> VAXeln --> Mica
DEC VMS  --/

Cutler took the concept of a microkernel from CMU Mach and combined it
with design concepts he had used in VMS to create a real-time OS for
the VAX called VAXeln.  DEC had several proposed machine architectures
for a RISC-based successor to VAX.  The one from Cutler's DECwest was
called PRISM.  Mica was the microkernel-based OS for PRISM.  The
intent was to build VMS and UNIX personality layers on top of the Mica
microkernel.  PRISM was cancelled in favor of Alpha, and that led to
Cutler's departure for Microsoft.

> When Cutler did Mica and then NT OS-2 he did not care what the user
> interface was.  Mica was a pure uk and NT OS-2 was also, but by the time of
> the product it became a hybrid.   Putting a different user interface, be it
> DOS, OS/2, Unix, VMS or Windows was in the kernel design.

As with Mica the original design was for various personality modules
(DOS, OS/2, Unix, whatever) to be layered on top of the microkernel.
The NT microkernel internals looked very familiar to VMS weenies such
as I.  Cutler was able to resist attempts to smear the layers by
putting hooks etc. in the microkernel, but over time the clean break
between the kernel and Windows has been muddied.

CMU Mach was the microkernel for Jobs's NeXT OS, and with BSD Unix
layered on top, was the basis for Apple's OS X.  OS X still uses the
Mach object file format, MACH-O.

-Paul W.

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