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From: wdm@ecn-pc.UUCP (William D Michael)
Newsgroups: net.arch
Subject: Re: uninitialized data
Message-ID: <392@ecn-pc.UUCP>
Date: Sat, 28-Sep-85 19:24:48 EDT
Article-I.D.: ecn-pc.392
Posted: Sat Sep 28 19:24:48 1985
Date-Received: Mon, 30-Sep-85 00:41:15 EDT
References: <436@uvm-cs.UUCP> <164@tulane.UUCP>
Reply-To: wdm@ecn-pc.UUCP (William D Michael)
Organization: Electrical Engineering Department , Purdue University
Lines: 35
Summary: 

In article <164@tulane.UUCP> jfk@tulane.UUCP (John Kreuter) writes:
>> 
>>   Laex Colvin asks about an architecture that traps on using uniniitialized
>> data.  The CDC 6000 series architecture does sort of.  An option to the loader
>> will cause all data locations to be filled with a bit pattern representing
>> "indefinite" which the CPU will choke on.
>> -- 
>> 							Stephen J. Hartley
>> USENET:	{decvax,ihnp4}!dartvax!uvm-gen!uvm-cs!hartley	University of Vermont
>> CSNET:	hartley%uvm@csnet-relay				(802) 656-3330, 862-5323
>
>This is an extremely high overhead way of checking for uninitialized data.

     Extremely high overhead, you say?  Please explain how this method is
     has a higher overhead than a tagged architecture.


>An alternative would be an architecture in which a small tag field identifies
>the type of the data.  This would have the further advantage of allowing, say,
>arithmetic operators to be overloaded as they are in high level languages.
>
>See "Advances in Computer Architecture", by Glenford J. Meyers (John Wiley
>and sons, 1978)

     Tags are nice, I'll grant you, but I think you are missing the boat here.
     Tags can indeed be useful for this sort of problem, but their real value
     comes from simplifying instructions set, and making os-type jobs easier
     to implement (ie, garbage collection).

>
>					John Kreuter

     Bill Michael
     (wdm@pur-ee)


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