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From: wayne@dsndata.uucp (Wayne Schlitt)
Newsgroups: comp.arch
Subject: Re: SCSI on steroids, mainframes move over
Message-ID: <WAYNE.89Aug23163411@dsndata.uucp>
Date: 23 Aug 89 21:34:14 GMT
References: <5932@pt.cs.cmu.edu> <1026@ks.UUCP>
Sender: wayne@dsndata.UUCP
Organization: Design Data
Lines: 42
In-reply-to: kurt@ibmarc.uucp's message of 22 Aug 89 17:41:55 GMT

In article <1026@ks.UUCP> kurt@ibmarc.uucp (Kurt Shoens) writes:
> In article <5932@pt.cs.cmu.edu> butcher@g.gp.cs.cmu.edu (Lawrence Butcher)
> writes about the new NCR SCSI chip and stipulates the following about
> business systems:
> 
> >The biggest, fastest business computers seem to run 1960's operating systems
> >without protection, and allow user programs to do I/O without OS assistance.
> >My new question.  Is fast I/O all that micros need to bury mainframes?  Or
> >is user level I/O needed?  If needed, how can simple hardware be built which
> >allows direct user level DMA I/O?
>  
> I was wondering what operating system this refers to.  IBM sells "TPF"
> [ ... ]

i was wondering about this too and the only thing i could come up with
is the "channel programs" that you can "execute" on most IBM mainframe
OS's.

of course the operating system has to go through and verify that these
channel programs are correct and dont do anything the user shouldnt be
able to do.  the operating system has to add a bunch of additional
CCW's and it does the real SIO instruction so it isnt really "user
level I/O".

for those of you who havent worked with this stuff, "Channel Command
Words" can be thought of as very simple instructions to a very simple
computer.  you can do a few things really well as a "channel program"
such as "skip until you find a tape mark, then skip until you find a
block with a certain key" all without the main cpu having to do any
work.  the "channel cpu" is the thing executing the channel program.
you can also do scatter/gather type i/o directly in a channel program,
no block moves needed.  one of the main limitations of the channel cpu
is that it doesnt know about virtual memory so any address must be
real addresses and you have to make sure the pages are locked in
memory.  

i really dont know if "channel programs" are that much better than a
good scsi board.  both systems offload the main cpu from all the
little hand holding needed to do most i/o.


-wayne