cliffhanger@cup.portal.com (Cliff C Heyer) (09/07/89)
(The HARDWARE Q's are intermixed below.) I'm planning to buy a 80386 PC for use with UNIX, MSDOS, OS/2, and WINDOWS/386. After studying the trade papers and marketing literature, I've made the following conclusions: (feel free to comment) 1. Price: 33MHz hardware about same ballpark as 25MHz hardware. 2. 33MHz hardware not yet reviewed in key areas of: bus speed, paged/interleaved memory, shadow (BIOS/video) RAM, disk cache(memory or controller), extended memory speed, wait states. 3. 100% of 33MHz hardware gives 10-20% better MIPS than 25MHz. 4. 33MHz hardware disk I/O only 0-5% better than 25MHz. In other words, it might as well be the same. 5. 80386 portables are about the same price as 33MHz desk hardware but are 50% slower in CPU and 70% slower in I/O. QUESTIONS about 33MHz 80386 PCs... (This is where I need the help!) 1. UNIX (or any multitasking OS) and the effects of the on-board cache: While multitasking, does flushing the cash waste a measurable amount of run time or is it insignificant compared to swapping, paging, and/or other overhead? In other words, is the cache still beneficial even though it is being flushed? (I assume "yes" since minicomputers such as all VAX models have them.) 2. Is memory technology (cost/speed ) lagging behind microprocessor technology? All the newest 33MHz 80386 PCs are using 70+ ns DRAMs when the 386 is running at 30 ns and the on-board caches are rated at 25 ns. You can't get 0 wait states 100% of the time with this approach. 3. Is it impractical (cost and/or size) to put 40 256KB 25ns SRAMs (no refresh overhead and cycle time=access time) up for main memory? In other words, is it cheaper to implement paged (PMRAM, SCRAM) or interleaved schemes to reduce wait states rather than use 40 SRAMs? It seems like alot of trouble to go to...but how much do SRAMs cost? 4. Are any board makers making (or have made) motherboards with ESDI and/or SCSI interfaces ON BOARD to bypass the 8MHz AT bus? Also hopefully this mfg. would include shadow RAM (BIOS & video) and extended/expanded memory that is as fast as main memory. (eg. add on memory boards have same cycle time as the first 2MB.) 5. I assume the ONLY thing that makes the 33MHz PCs faster is the 25 ns cache. Otherwise, with 70 ns DRAM the BEST you could do would be run as fast as a 16MHz 80386 PC (62 ns) but with lots of wait states. In other words, memory cycle time limits non-cache CPU performance to that of a 16MHz 80386. 6. If you whipped out your trusty soldering gun and anti-static gear and changed all your memory chips to 25 ns SRAMS(on a 33MHz machine w/no cache) would the wait states go away? OR is the timing part of the hardware architecture? (Pardon me for this seemingly naive question, but I've been doing software for 8 years.) 7. The PC manufacturers never talk about parity error checked memory, ECC memory, Harvard A.(separate data/instruction cache), data write-thru cache, write buffers (CPU can go on after issuing write instruction only), and multi-word memory transfers. Are PC mfgs behind the times? Or is this because of all the canned stuff from the east. 8. Is there ANY manufacturer who has fully exploited the power of the 80386 chip? That is, at 33MHz is there any hardware that... >can support sustained disk I/O >1MB/sec by bypassing the AT bus via on-board controllers, or using VME, etc., >has "real" 100% zero wait state memory (probably SRAM), AND expanded/extended memory boards (no wait states 100% of the time), >(for PCs) has shadow RAM (BIOS & video), >gives you several "real" 32-bit "backplane" slots and controllers for them (Intel or Zeos?), >operates FCC class B. Please POST your comments.
jcm@mtunb.ATT.COM (was-John McMillan) (09/08/89)
Maybe we should just give up and rename this group ];-) Suggestions? unix-pc.no_not_that_1 unix-pc.unknown.but_loved unix-pc.secret_army Who submits to UN_READ groups? Not FLAMING... juzz puzzled? john mcmillan -- att!mtunb!jcm
wilkes@mips.COM (John Wilkes) (09/08/89)
In article <21937@cup.portal.com> cliffhanger@cup.portal.com (Cliff C Heyer) writes: > >I'm planning to buy a 80386 PC [...deleted...] boy, i sure do get tired of seeing this kind of crap floating in unix-pc.general. seems like every week or two some dweeb posts an article with a bunch of questions about '386 boxes, xenix vs. unix, etc., etc. i predict it will only get worse as the net reaches more and more folks. maybe we should revive the discussion about changing the name of unix-pc.* and/or joining the "mainstream" feed (i.e., become comp.sys.att.something) (if not for thad, i would launch into my diatribe about portal users...) -- -wilkes wilkes@mips.com -OR- {ames, decwrl, pyramid}!mips!wilkes