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From: koziol@yoyodyne.ncsa.uiuc.edu
Newsgroups: comp.sys.ibm.pc
Subject: Re: Whis is fastest 386/33 or 486/25 ?
Message-ID: <17200007@yoyodyne>
Date: 12 Jul 90 21:03:00 GMT
References: <205440@<1990Jul5>
Lines: 14
Nf-ID: #R:<1990Jul5:205440:yoyodyne:17200007:000:664
Nf-From: yoyodyne.ncsa.uiuc.edu!koziol    Jul 12 16:03:00 1990


One of the main reasons for the '486 being about twice as fast as the '386
is because of the way the chips are clocked.  The '386 (and also the '030
BTW) use a divide-by-two clock from the system clock to actually clock the 
internals of the chip.  The '486 (and the '040) are syncronously tied to the
system clock, i.e. they actually clock at 25Mhz at a system clock of 25Mhz
as opposed to the '386 which is internally dropped to 12.5Mhz at a 25Mhz
system clock.
	I would assume the additional speedups are due to a tighter coupling
of the math coprocessor and cache controller, and also some optimization
of the silicon.

		Quincey Koziol
		koziol@ncsa.uiuc.edu