Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!zaphod.mps.ohio-state.edu!wuarchive!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga Subject: Re: motorola/intel Message-ID: <14427@cbmvax.commodore.com> Date: 13 Sep 90 22:27:21 GMT References: <30140@nigel.ee.udel.edu> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 65 As Larry has said here, it is impossible to both understand and appreciate the Intel architecture. In article <30140@nigel.ee.udel.edu> thamilton@ch3.intel.com (Tony Hamilton, WF1-81, x48142) writes: >To whoever posted the idea that Intel chips just don't compare to Motorola's, >I can not agree more. They DON'T compare, because they follow two entirely >different principles. Motorola utilizes memory-mapping, while Intel uses >Isolated I/O. You're missing the point. First of all, dedicated I/O instructions are an extremely archaic concept. I imagine the only reason they existed on the 8088 in the first place was because the 8088 was designed to be relatively close to assembly-source level compatible with 8080/8085 machines. The use of this technique in the 8080 was mainly to get around address space limits (you could have 64K AND I/O devices at once), but it's a horrible waste of instruction decoding, and the rest of the world does fine without it. You will find that this architectural foolishness is just about nonexistant outside of the 80x86 family. Even other Intel chips, like the i860, do things the modern way, by memory mapping. I don't know of any modern microprocessor that supports I/O-only instructions. The generic objections to the Intel architecture, however, have absolutely nothing to do with I/O mapping. They have to do with segmentation. Segmentation is one of the more truely evil concepts in the microprocessor industry. Again, this was something Intel adpoted to make the transition from 8080 to 8088 less painful. It worked to that end, but has been causing endless pain every since. Motorola, which was in a similar position in the 70's, chose instead to scrap any notions of pseudo-compatibility with their 8-bit line, and instead do a 16 bit microprocessor correctly. Their solution was to make the programmer's model a full 32 bit model, rather than kludging around with a 16 bit model and some banking scheme (eg, everyone then knew that 64K of addressing wasn't enough). The end result has been that every subsequent generation of Motorola 680x0 uses the same programmer's model. Every generation of Intel 80x86, execept for the 80386->80486 jump, has had a new programmer's model and special hardware modes to support the old models. The reason they 80486 has the same model as the 80386? The 80386 was the first 80x86 CPU to support a true 32 bit programmer's model, which made segments unnecessary. So there was no reason to change anything. >The unfortunate thing is that most users can only see the advantages of >memory-mapping, while Intel chips are appreciated most in the high end of >the market. The Intel 80x86 architecture isn't appreciated anywhere near the high end of any market. It's used by folks who find 80486 machines a good bang/buck, or by folks who find that the installed base of 30-40 million MS-DOS machines and growth of another 10 million or so a year tends to make rather esoteric programs available on the market. Or by people who don't know any better. But there are few, if any, people who choose 80x86 machines because they admire their architecture. And I'm willing to bet just as many people buy Ford Escorts for their styling. >Defending Intel interests across the globe... Now there's a lost cause... > Tony Hamilton -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy Get that coffee outta my face, put a Margarita in its place!