On Fri, 24 Jan 1997, Christoph Ewering wrote:

> Hello guys!
> 
> Could someone explain to me why it is so difficult for a Unix-system to
> hold the time.

Well, on the Mac, the clock's interrupt isn't very high, relative to other
things in the system (like SCSI and serial ports).  So, if the clock ticks
while we're busy doing something else, we miss the interrupt.

> I think Scott reported that his SE/30 looses 9 hours during
> compiling a whole night. That's a lot.

Yep, but I'm pretty sure Scott is using the sbc SCSI driver, which AFAIK
does not do interrupt-driven transfers (ie, Pseudo-DMA).  So, it spends
large amounts of time with the clock interrupt blocked.

I've done some 3-day-long `make build' sequences, and only lose a few
minutes per day with the ncr SCSI driver.  Then again, when I use my tape
drive (which I've forced the ncr driver to use polled vs PDMA transfers),
I lose clock ticks at the rate of 15% to 25%.