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From: aglew@oberon.crhc.uiuc.edu (Andy Glew)
Newsgroups: comp.os.research
Subject: Re: Extremely Fast File Systems
Message-ID: <5825@darkstar.ucsc.edu>
Date: 31 Jul 90 12:52:10 GMT
Sender: usenet@darkstar.ucsc.edu
Organization: University of Illinois, Computer Systems Group
Lines: 38
Approved: comp-os-research@jupiter.ucsc.edu

>>Why not: CPU speed
>>------------------
>>
>>A Sun 4/490 is a reasonably fast machine.  Moving I/O requires a copy.
>>The 490 has copy hardware that maxes out at 25 MB / sec in the kernel
>>and 14 MB / sec in user space.  
>
>Larry:
>
>    I've heard the discussions about busses and disk drives before
>but this is the first time someone's said CPUs will be a problem.

Actually, it's not CPU speed, but the CPU-memory interface that's the
problem.
    The CPU-memory interface is increasing in speed, but nowhere near
as fast as CPUs.  Caches do not help large copies from I/O to user, if
I/O is uncached (even if cached it can be a problem, with a single
data port on the cache).  Burst protocols and wider busses seem to be
the favoured solutions.

--
Andy Glew, andy-glew@uiuc.edu

Propaganda:
    
    UIUC runs the "ph" nameserver in conjunction with email. You can
    reach me at many reasonable combinations of my name and nicknames,
    including:

    	andrew-forsyth-glew@uiuc.edu
    	andy-glew@uiuc.edu
    	sticky-glue@uiuc.edu

    and a few others. "ph" is a very nice thing which more USEnet
    sites should use.  UIUC has ph wired into email and whois (-h
    garcon.cso.uiuc.edu).  The nameserver and full documentation are
    available for anonymous ftp from uxc.cso.uiuc.edu, in the net/qi
    subdirectory.