gnu@l5.uucp (John Gilmore) (10/28/85)
It's certainly possible that a single 68020 in a lab can be pushed to 32MHz. It helps a lot, as was pointed out by someone from Intel in another newsgroup, to change the voltage and to cool the chip as much as possible. Getting a sample running 32MHz with freon spray on it is different from being able to produce chips that run that way across the full temperature and voltage range. But if the rumor is true, it does indicate that the chip is limited by power or temperature or fabrication tolerances (mechanical design), rather than by switching speed or electronic design. One technique usable to see what parts of the chip are limiting it is to run it at various clock rates and see what kind of failures appear. This may be where this 32MHz 68020 is being used. For example, the kind of errors that have been described on Vax 785's (carry propagation across 30 bits) might crop up, indicating that the adder is the next bottleneck. Chips run this way are not really expected to function; they're expected to point the way by how they fail. The next time the chip mask is fixed up, they can improve the adder, which probably improves the yield of 16.67MHz chips and 12MHz chips too.
norm@rocksanne.UUCP (11/01/85)
> full temperature and voltage range. But if the rumor is true, it does > indicate that the chip is limited by power or temperature or > fabrication tolerances (mechanical design), rather than by switching > speed or electronic design. I am not clear on what you are saying here, the speed of the chips is really limited by switching speed. Improvements in the fab lines or finer geometries will help improve the switching speed by either reducing loads or improving drive currents. The temperature issue is something common to all silicon MOS devices. In a simple sense, the speed is limited by how fast you can drive rc loads. The drain current for a MOS device has a term in it that decreases as temperature increases. Some of the data I have seen from MOS devices that we have done, and SPICE simulations indicate that for a rise from 27C to 50C the speed of MOS devices will decrease about 10%. Cooling the devices will increase the drain current and hence the switching speed. There is actually a company (a CDC or Cray spin off ?) that is planning to market a "supercomputer" that uses CMOS gate arrays to build a processor and runs the devices at 70K. They claim a 2x-3x speed improvement over room temp (this info is a little sketchy in my memory but most of the data should be close). Given that the 020 runs at some where between 16-20Mhz then 32-60 Mhz chips are possible with this technique. However, the implementation details of such a system interconnect etc are not trivial. Also the temperature decrease that helps in MOS devices makes bipolar devices run slower, so the interface circuits, if bipolar would not want to be cooled. -------------- Norm Zeck Xerox Corp. 800 Phillips Rd. 128-29E Webster N. Y., 14580 ARPA: NZeck.Wbst@Xerox.arpa UUCP: {decvax, allegra, seismo, cmcl2}!rochester!rocksanne!norm Phone: [USA] (716) 422 6246 --------------