Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!voder!nsc!amdahl!JUTS!duts!kls30 From: kls30@duts.ccc.amdahl.com (Kent L Shephard) Newsgroups: comp.sys.amiga.advocacy Subject: Re: 680x0 vs 80x86 Message-ID: Date: 26 Jun 91 17:59:18 GMT References: <92@ryptyde.UUCP> <4671.tnews@templar.actrix.gen.nz> <1154@stewart.UUCP> <1991Jun25.165516.13021@mintaka.lcs.mit.edu> Sender: netnews@ccc.amdahl.com Reply-To: kls30@DUTS.ccc.amdahl.com (PUT YOUR NAME HERE) Organization: Amdahl Corporation, Sunnyvale CA Lines: 61 In article <1991Jun25.165516.13021@mintaka.lcs.mit.edu> rjc@churchy.gnu.ai.mit.edu (Ray Cromwell) writes: >In article <1154@stewart.UUCP> jerry@stewart.UUCP (Jerry Shekhel) writes: >>jbickers@templar.actrix.gen.nz (John Bickers) writes: >>> >>> It's usually because if you have a split cache you break programs >>> that use self-modifying code. >>> >> >>Doubtful, John, since every OS in existence treats code as data when it >>loads it into memory for execution. > > But this is different, Jerry, because in this case the OS KNOWS >how to clear caches. If a lot of MS-DOG programs used self-modifying >programs, or if the OS itself doesn't know how to treat caches, >code will break. Hence, Intel probably keeping I&D unified to avoid >an MS-DOG nightmare. Wrong. Intel decided to go with a unified cache for one because it is simpler to implement. Also if you have a 4 way set assoc. cache you have basically 4 small caches. Also in Intel processors you have instuctions that have data included or immediately following. Kind of hard to separate data and instuctions. Moto went with a seperate cache because the architecture is different. The type of instructions are different. As for self modifying code. The machines that use Moto processors are more guilty of this. The Mac and Atari machines uses self modifying code for copy protection. When Moto started putting small caches on their chips it created a nightmare. Self modifying code would have broken the 386 with cache. Also if a cache is designed properly it should be completly transparent to software. > > >>>-- >>>*** John Bickers >>-- >>+-------------------+----------------------+---------------------------------+ >>| JERRY J. SHEKHEL | POLYGEN CORPORATION | When I was young, I had to walk | >>| Drummers do it... | Waltham, MA USA | to school and back every day -- | >>| ... In rhythm! | (617) 890-2175 | 20 miles, uphill both ways. | >>+-------------------+----------------------+---------------------------------+ >>| ...! [ princeton mit-eddie bu sunne ] !polygen!jerry | >>| jerry@polygen.com | >>+----------------------------------------------------------------------------+ > > >-- >/ INET:rjc@gnu.ai.mit.edu * // The opinions expressed here do not \ >| INET:r_cromwe@upr2.clu.net | \X/ in any way reflect the views of my self.| >\ UUCP:uunet!tnc!m0023 * / -- /* -The opinions expressed are my own, not my employers. */ /* For I can only express my own opinions. */ /* */ /* Kent L. Shephard : email - kls30@DUTS.ccc.amdahl.com */