Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!cornell!rochester!ur-tut!ur-valhalla!micropen!dave From: dave@micropen (David F. Carlson) Newsgroups: comp.sys.ibm.pc Subject: Re: Intel 386SX chip & its applications Summary: rash generizations Message-ID: <513@micropen> Date: 28 Jun 88 18:42:33 GMT References: <206900116@prism> <6734@cup.portal.com> <6859@cup.portal.com> Organization: Micropen Dirent Writing Systems, Pittsford, NY Lines: 41 In article <6859@cup.portal.com>, mslater@cup.portal.com writes: > > As for 286 vs 386 speed, I've seen a number of benchmarks that show that for > 16-bit code (8086 or 286 code) the 286 runs very nearly the same speed, and > sometimes slightly faster, than a 386. There are many instructions that > require fewer clocks on a 286 than on a 386. The primary advantage of the > 386 is that it can fetch two 16-bit words at a time; however, this apparently > is not such an advantage, presumably because the pipeline can be kept nearly > full with only 16-bit fetches and because at every jump there is a 50/50 > chance that the second word fetched must be thrown away. The 32-bit bus of > the 386 obviously has a big advantage for programs that manipulate lots of > 32-bit data words, but most programs are dealing with bytes or 16-bit words. Most programs deal with word size for the machine. Most useful programs I have used have 32 bit ints and floats. I can run "useful" programs on the 386SX, whereas I lost much hair running most anything "useful" on the 80286. > > If anyone else has any insights on 286 vs 386 performance, I'd appreciate any > clarifications. The data I've seen indicates that nearly all the performance > gain of 386 systems over 286 systems, when running DOS or OS/2, is simply due > to the faster clock, and that the 32-bit bus is of little help. > Michael Slater, Microprocessor Report 415/494-2677 > mslater@cup.portal.com sun!portal!cup.portal.com!mslater The stipulation of DOS or OS/2 is probably correct. The 386 requires more time to do segment loads due to 2 levels of tables indirection whereas the 286 has just a GDT, LDT, etc. The big point of the 386SX is that you don't have to close the door on Xenix, UNIX, OS/2-386, etc. just because the 32bit memory scene is such a mess now. For most single user apps (workstation model), a 16 bit data bus is not as much of a bottleneck as is the 250Kbps of the WD MFM disk controller. Speed isn't the big question but future compatibility is. -- David F. Carlson, Micropen, Inc. ...!{ames|harvard|rutgers|topaz|...}!rochester!ur-valhalla!micropen!dave "The faster I go, the behinder I get." --Lewis Carroll