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From: farren@gethen.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: NOP
Message-ID: <193@gethen.UUCP>
Date: Thu, 1-Oct-87 01:08:19 EDT
Article-I.D.: gethen.193
Posted: Thu Oct  1 01:08:19 1987
Date-Received: Sat, 3-Oct-87 06:32:34 EDT
References: <2306@sphinx.uchicago.edu> <4478@amd.AMD.COM> <309@ncrcan.UUCP>
Reply-To: farren@gethen.UUCP (Michael J. Farren)
Organization: Sci-Fido - Unix in Oakland
Lines: 30
Keywords: NOP

In article <309@ncrcan.UUCP> brian@ncrcan.UUCP () writes:
>In article <4478@amd.AMD.COM> ching@amd.UUCP (Mike Ching) writes:
>>.... The NOPs are never executed and don't slow down the
>>processor.
>>
>>mike ching
>
>Sorry, but the NOPS are always executed (how would the processor know that
>it is in fact a NOP, if it didn't execute it) and each execution takes 
>a finite, albeit minimal amount of execution time.

Sigh.  Given an instruction sequence like:

	jmp    label
	nop
label:

the NOP will NOT be executed, and, in fact, barring certain aspects of
pipelining, will never even be SEEN by the processor.  Control flow
will jump right over that instruction every time.  The processor, in fact,
does NOT know that the instruction is a NOP - it knows nothing about it
at all - it could be any value, but is a NOP for convenience and
readability.


-- 
----------------
Mike Farren             "... if the church put in half the time on covetousness
unisoft!gethen!farren   that it does on lust, this would be a better world ..."
gethen!farren@lll-winken.arpa             Garrison Keillor, "Lake Wobegon Days"