Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!know!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!jarthur!nntp-server.caltech.edu!ziggurat!tim From: tim@ziggurat.gg.caltech.edu (Tim Kay) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: 386sx Motherboard Message-ID: Date: 4 Oct 90 22:18:02 GMT References: <1990Oct3.173937.995@urz.unibas.ch> <1990Oct4.141439.1039@eng.umd.edu> Sender: news@nntp-server.caltech.edu Organization: California Institute of Technology, Pasadena Lines: 90 Nntp-Posting-Host: ziggurat.gg.caltech.edu >> I'm in the market of a 386sx motherboard, and I need to know some info. >>First of all, this guy wants to offer a 386sx 16Mhz with a fast crystal >>installed to yield 20Mhz (he says Norton SI is 21). Is this a safe thing >>to do? >It is not safe. While you might get lucky and get a chip that's >actually capable of 20MHz operation but just isn't certified for it, >more likely you'll be replacing the SX within a few hours. Unless the >chip is actually specified for 20MHz, it probably can't dissipate the >heat generated by the faster speed very well and will consequently >fail. As you've worded it, this loser is trying to load you up with a >motherboard that's also running above design speed. What goes for the >SX chip also goes for the other chips on the board, so you'll probably >have trouble with random failures. This is incorrect. Typically, there is absolutely no difference between the fast and slow parts that a manufacturer ships, *except* that the faster parts happen to work at the faster speed. After Intel manufactures each 386 chip, their tester determines how fast it can run reliably and stamps it accordingly. The only difference is that certain parts of the chip layout turn out to be marginal, and some of the chips manage to squeak past the tester, due to many factors including process variations, while others don't. The chips will generate roughly the same amount of heat regardless of their stamped speed rating. As part of tuning the process to produce faster chips (on average), they might redesign certain marginal parts of the mask or process. This tuning of a process slowly increases the mean speed of the chips coming off the line. The question of whether a given chip will run at a faster rate than it is stamped must really be broken into two separate cases. If you are trying to push the chip faster than the fastest chip that a manufacturer "makes," you are in case I. If you are just trying to save money by buying a less expensive chip, you are in case II. Case I: What do you suppose Intel does with a chip that passes not only the 33 MHz test but also passes the 40 MHz test? (I would guess they run the 40 MHz test and the 50 MHz test so that they can measure how well the line is maturing.) But they haven't announced a 40 MHz part, so they have to sell it stamped for 33 MHz. This is why you *can* screen a bunch of 33 MHz chips and find a few that will run just fine at a higher clock rate. The only suspicious part of it is that the screeners test equipment isn't as good as Intel's. But the fact that the chip is stamped 33 MHz doesn't mean that the chip failed Intel's faster tests. Case II: The question of whether a 16 MHz part will run at 20 MHz when the manufacturer is shipping 20 MHz parts is a different question. If a chip passed the 20 MHz test, the manufacturer would probably then sell it as a 20 MHz part. Therefore, if a chip is stamped 16 MHz, it probably failed the manufacturer's 20 MHz tests. However, manufacturer's tests are harsher than most environments that the chips end up in eventually. It is just possible that the circumstance in which the 16 MHz chip failed when tested at 20 MHz will never occur in the particular application. Also, what happens when a manufacturer's line has matured to the point that most of the chips are coming out at at least 20 MHz. Do they stop selling 16 MHz parts? Eventually they do, but for marketing reasons, they might choose to stamp some 20 MHz-capable parts as 16 MHz. Otherwise, they would have to force 16 MHz customers to buy the more expensive 20 MHz parts, or they would have to lower the price of the 20 MHz parts for the entire customer base. There is no reason that they manufacturer's process will mature at exactly the same rate as the demand for faster chips. -------- I have very successfully "pushed" chips. I ran a one wait state AT clone at zero wait states for about two years. I then replaced the motherboard with a 20 MHz 386 motherboard, but the 386 was rated at only 16 MHz. It has been running fine for the last two years. I bought the 386 motherboard when 20 MHz 386 chips were relatively new, so this 386 might qualify as a case I chip. However, let me say that I am not suggesting that you go out and save money in this way. You don't want to mess with these things unless you are capable and willing to deal with potential problems that might occur. Many people might attribute certain hardware problems to software or visa verse. The only way to point the finger in the correct direction is to run the software (*all* the software) on a different machine. If you aren't willing to chase down these loose ends, go with a more conservative system. Tim