Xref: utzoo comp.lang.c:11344 comp.arch:5515
Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!amdahl!nsc!voder!apple!baum
From: baum@Apple.COM (Allen J. Baum)
Newsgroups: comp.lang.c,comp.arch
Subject: Re: Self-modifying code
Message-ID: <14017@apple.Apple.COM>
Date: 15 Jul 88 16:46:51 GMT
References: <3353@cognos.UUCP> <619@goofy.megatest.UUCP> <429@uwovax.uwo.ca> <33518@yale-celray.yale.UUCP> <1087@ficc.UUCP>
Reply-To: baum@apple.UUCP (Allen Baum)
Organization: Apple Computer, Inc.
Lines: 14

[]
>In article <1087@ficc.UUCP> peter@ficc.UUCP (Peter da Silva) writes:
>I have a question:
>
>	Why are an Icache plus a Dcache better than just
>	a big shared cache as big as both?

In terms of hit/miss ratios, a unified cache is clearly better. However, in
terms of effective access time, a split I/D cache is better. This is because
both can be accessed simultaneously, instead of one having to wait for the
other to finish. If both are getting accessed simultaneously (which should
happen 40% of the time, if Loads/Stores account for %40 of instructions), then
this more than offsets the increase in miss ratio.

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