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From: blackman@eniac.seas.upenn.edu (David Blackman)
Newsgroups: comp.arch
Subject: Re: Are all RISCs the same?
Message-ID: <5116@netnews.upenn.edu>
Date: 11 Sep 88 15:57:26 GMT
References: <58@zeno.MN.ORG> <6903@aw.sei.cmu.edu> <22860@amdcad.AMD.COM> <6930@aw.sei.cmu.edu> <5692@sundc.UUCP>
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Reply-To: blackman@eniac.seas.upenn.edu (David Blackman)
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In article <5692@sundc.UUCP> bwong@sundc.UUCP (Brian Wong) writes:
>
>While I can certainly agree that having a lot of cpu state will certainly
>make it much harder to make a good hard real time machine, it is not at all
>clear that a "good hard real time machine" will necessarily be what a large
>part of the [workstation,minicomputer,pc,minisuper] will want.  
>

I don't know if you are objecting to "good", "hard", or "real-time" but
I would argue that you certainly want "good" and "real-time" machines.

Real time, predictable performance is one of the most important advantages
that a workstation affords.  The large variance in response time on normal
time sharing computers was one of the factors which inspired the development
of workstations.  Jim Morris from Xerox PARC said one of the advantages of the
Alto is that is doesn't run faster at night.  This point seems to have
ignored/overlooked by most workstation manufacturers.  For example, I use
a diskless workstation whose file system is stored on another workstation.
My response times are highly dependent on the load of the file system
workstation.  

The workstation offers the potential of allowing users [NOT "kernel
hackers"] to write software that requires response time in the range of
100 us - 1 ms.  This was impossible with conventional time sharing computers.

You may be using a remote procedure call.  You may have written your
own driver for a serial I/O port.  You may have just interfaced a CD-ROM
player to your workstation and are writing a driver for it.  You may
be trying to drive a 60 ppm laser printer.  You may be trying to send/
receive speech over a network in real time.  Or, you may be experimenting
with a new network protocol.

In all cases, the system must provide the facilities for users to
write software that has high performance, can keep up with most external
devices and events, and have uniform response time.  This sounds like
real-time to me.

Blackman@eniac.seas.upenn.edu