🚀 go-pugleaf

Maynard Handley <maynardh@apple.com> wrote:
>
>
>Once upon a time you were telling us the MacOS designers were fools for 
>not including VM and pre-emptive multi-tasking in the system. 
>In the above postings you reveal a complete lack of understanding of the 
>issues related to pre-emption. The difference between a UNIX style OS and 
>a Mac style OS is that the UNIX OS never revelealed any global state to 
>apps to play around with. If it had, that UNIX OS would also have to jump 
>through hoops to try to add pre-emptive multi-tasking to the system.

I don't remember saying anything much about VM.  In point of fact most
of my experience is with RSX, not UNIX.  Apple was foolish not to implement
multitasking from the start.  I don't believe they had the option of
providing separate address spaces at first -- it should have been
implemented immediately upon having the hardware.

>
>In fact, this exact same issue DOES arise in a UNIX system. You cannot, 
>(in the UNIX systems I know of) make X-windows calls from an interrupt 
>handler. Instead you have to set flags and then poll those flags in your 
>main X event loop. The reason is exactly the same as what's going on with 
>the mac---the X server serializes itself at the process level and if 
>interupted while in the middle of a call, global state is corrupted 
>and X for the system is frozen.

Don't know much about X.  I do know that X and UNIX are not the same
thing.

>
>Next consider that Netware, generally considered the speed standard which 
>other server OS's try to reach, runs with neither Protected Memory nor 
>Preemtive Multi-tasking. This was (and remains) a deliberate decision.
>These PMs are not free, and in some situations the code involved has a 
>better idea of when to relinquish the CPU than does the scheduler.

I don't see how Netware is relavent, but I'll grant that there are
instances where PM is not the best approach.  I've said that here
myself.  PM is generally not a good idea when one application has
total control of the machine.  This situation is not true for
either the Mac or the PC.  (It was true under DOS for the PC, but
I'll certainly not argue that this was a proper state of affairs.)

>
>Finally, I have to appreciate the candor of your comment on VM.
>So when you chosen OS doesn't do SMP because there are "too many 
>synchronization issues" that's OK, but when the MacOS doesn't do
>Preemtive Multi-tasking because e are "too many synchronization issues" 
>that's not OK. I guess the important thing was that you judged 
>each case on the technical issues not on the vague basis that you 
>understand very little of the issues involved but will nonetheless stand 
>by UNIX come hell or high water because that's your team.
>
>Maynard

Aside from the fact that I understand that SMP is being worked upon
for Linux, I don't believe you read my post correctly.  I said that
SMP didn't look like such a big deal (not VM).  In fact, it seems to
me that the hardware folks are yet again making another stupid
mistake.  It seems to me that a more flexible system could be
achieved if some networking capability was built into the chip
instead.

-- 
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