[TUHS] UNIX on S/370

Larry McVoy lm at mcvoy.com
Tue Nov 21 12:41:11 AEST 2017


So tape I can see being more weird, but isn't raw disk just "don't put it
in buffer cache"?

>From what I've been able to gather early tape in Unix was dicey, something
about the driver doing seek.  Was there more to it than that?

On Tue, Nov 21, 2017 at 02:33:55AM +0000, Clem Cole wrote:
> It???s not so much that they don???t mix, it???s not quite the same.    Some
> coprocessor ideas work really well into the Unix I/O model, others don't.
>  Raw disk and tape I/O ala a PDP11 or VAX for instance is not easy on an
> IBM channel controller or a CDC PPU.
> 
> 
> 
> 
> 
> 
> 
> 
> On Mon, Nov 20, 2017 at 6:45 PM Larry McVoy <lm at mcvoy.com> wrote:
> 
> > On Mon, Nov 20, 2017 at 06:43:28PM -0500, Ron Natalie wrote:
> > >
> > >
> > > > I get that PDP-11 and VAX used memory mapped I/O but was that somehow
> > > exposed above the device driver layer?  If so, I missed that, because I
> > had
> > > no conceptual or technical problem with talking to an I/O
> > >
> > > > channel, it was pretty easy.  And I suck at writing drivers.
> > >
> > > There's nothing that restricts a device driver to memory mapped I/O.
> > You
> > > do what ever you have to do to initiate the I/O.   Even the x86's
> > originally
> > > used special instructions to start the I/O (in/out).    The DENELCOR HEP
> > > supercomputer (we did this port around 1983) we had to bounce I/O
> > requests
> > > off a separate I/O processor different from where the kernel was running.
> > > Similar constucts were used on other machines.
> >
> > Yeah, that's what I thought.  But other people were saying that I/O
> > processors and Unix didn't mix.  I don't get that, seems like whatever
> > the model is is hidden under the driver, that's the whole point of the
> > driver design is it not?
> >
> -- 
> Sent from a handheld expect more typos than usual

-- 
---
Larry McVoy            	     lm at mcvoy.com             http://www.mcvoy.com/lm 


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