Portable OS's (was: Re: Do OS's slow down with age?)

[Don Stokes, Govt Print, Wellington]

In article <579 at mcl.UUCP>, stacy at mcl.UUCP (Stacy L. Millions) writes:
> Being able to modify the OS to run on a new peice of hardware is
> what I consider portable. I challenge you to port VMS to run on
> an 80286, pull that off and I will beleive the VMS is portable.

Can I point out that MS-DOS only works on an 80386 because the 80386 is capable
of pretending to be an 8088, which is the *ONLY* processor that MS-DOS will run
under.  I challenge you to run MS-DOS on a 68000.  MS-DOS will *NOT* run on
an 80386 which is actually behaving as an 80386.

The whole purpose of an operating system is to provide a buffer between the
applications program and the physical hardware and architecture of the machine.

People who have been brought up in a MESS-DOS world will not understand this,
as the MS-DOS does not acheive this basic aim ... to do anything useful under
MS-DOS you have to go straight into the hardware and control the machine
directly, and occasionally modify the OS accordingly.  On a *REAL* OS, there
is never any need to do this.

VMS is "portable" among VAX computers.  It provides bridges in functionality
which blend in so well that few VMS users/programmers are even aware that 
there are differences in the architectures between different VAXes (eg many 
of the MicroVAX instructions are emulated by the OS).  

While I am not convinced that Unix is really "portable", it is as close as 
you can reasonably expect to get given the vast range of harware it will run 
on.  Since it is native mode, it has to be source language portable, as 80386
code will *NOT* run on a 68000 or VAX, no matter how hard you push it.  

Are you asking that *EVERY* machine ever built should be identical so that 
they can run the same OS code?  I repeat a comment made here already: Get real!

Regards,
	Don Stokes,
	Systems Programmer,
	Government Printing Office, Wellington, New Zealand.