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Path: utzoo!watmath!watcgl!dmmartindale
From: dmmartindale@watcgl.UUCP (Dave Martindale)
Newsgroups: net.unix-wizards
Subject: Re: movc3 is NOT always faster!
Message-ID: <2283@watcgl.UUCP>
Date: Mon, 19-Mar-84 17:17:38 EST
Article-I.D.: watcgl.2283
Posted: Mon Mar 19 17:17:38 1984
Date-Received: Tue, 20-Mar-84 00:57:15 EST
References: <5949@umcp-cs.UUCP>
Organization: U of Waterloo, Ontario
Lines: 7

Movc[35] normally does 32-bit writes to memory, at least on the 780.
Reads are always 64 bits due to the cache.  The actual data transfer
is slower than doing a movq, since 4 SBI cycles are required for 2 32-bit
writes vs. 3 for one 64-bit write.  Also, if you have the old MS780C
memory controller, a 32-bit write has to do a read-modify-write cycle
for any write smaller than 64 bits.  The new controllers don't have
this problem.