Date: Fri, 26 Jun 1998 08:41:11 -0700 (PDT) From: David Wolfskill <dhw@whistle.com> To: newbies@FreeBSD.ORG Subject: Re: Reference: Unix in 20-30 years Message-ID: <199806261541.IAA09741@pau-amma.whistle.com> In-Reply-To: <35932437.48E4@concentric.net>
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>Date: Thu, 25 Jun 1998 22:31:51 -0600 >From: ML Duke <mlduke@concentric.net> >Its actually somewhat difficult for a single user with over 8 megs of >ram to keep the cpu busy if its over 486/66. ??!? OK... I'll grant that this is -newbies -- but sometimes I think a bit of a reality check is in order. About the only way for the CPU to be idle is to ensure that it doesn't have enough work to do. This may be accomplished by either a lack of work queued, or a bottleneck that prevents the work form getting to the CPU. An example of the former might be a machine that's being used for nothing more demanding than a sole person playing solitaire; most of the time is spent waiting for input. (This is exacerbated in a non-X environment, since X needs to be concerned about all kinds of external events -- mouse movements, button pushes, & the like, which a "dumb TTY" interface just waits for characters (essentially).) Examples of the latter would be a machine that is starved for real memory (so it needs to swap processes in & out of memory; in extreme cases, this can lead to such an imbalance that the machine spends so much time swapping that it doesn't spend enough resources actually doing the desired work to get it done; this is known as "thrashing"), or that is waiting on (say) disk or tape I/O. (Actually, these two can be combined in truly "interesting" ways to exacerbate each other; this is one reason a fast I/O subsystem is important to total system design -- it does no good as far as getting a program run quickly if you've got the fastest CPU in the world, but you can't get the data into the CPU at a reasonable rate: the process, as a whole, will have I/O as a bottleneck. And swapping is a form of I/O....) In practice, for example, I might have picked up a new program (for example, the "ssh" distribution), unpack it, start the configuration for it; once that's started, open up another window & fetch (say) the "amanda" distribution. Go back to "ssh" & type "make", then go back to amanda, unpack that & configure it. Start reading news, go back to amanda & type "make".... Or, if you just want to burn CPU cycles, there's an algorithm for summing the reciprocals of the factorials -- works out to be "e" (the base of natural logarithms, a transcendental irrational number, the value of which (in decimal) is approximately 2.718281828459045...). I've calculated it to several thousand decimal places.... :-) Cheers, david -- David Wolfskill UNIX System Administrator dhw@whistle.com voice: (650) 577-7158 pager: (650) 371-4621 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-newbies" in the body of the message
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