Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site oakhill.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!godot!harvard!seismo!ut-sally!oakhill!doug From: doug@oakhill.UUCP (Doug MacGregor) Newsgroups: net.micro.68k Subject: 68020 performance Message-ID: <230@oakhill.UUCP> Date: Wed, 31-Oct-84 16:54:28 EST Article-I.D.: oakhill.230 Posted: Wed Oct 31 16:54:28 1984 Date-Received: Fri, 2-Nov-84 05:01:33 EST Organization: Motorola Inc. Austin, Tx Lines: 104 I understand the motivation behind the note authored by Joe Falcone concerning the comparison of the 68020 and a VAX. In principle I agree with his comments. I understand that my figures representing the performance of the 68020 can be taken out of context by those with a marketing or sales bent to unfairly compare a processor with a system. In all of the work that I have done, I have been very deliberate in avoiding comparisons with any system. Because comparisons of this sort are so simplistic and erroneous, I never felt that they were an issue to anyone who knew how computers worked. However, I strongly disagree with some of the interpretations that Mr. Falcone has drawn as well as some of the conclusions made. First, the interpretations of the 68020 performance are a bit narrow. The note implies that there are no applications except systems equivalent to a VAX. These non-system applications which include real-time robotics, graphics, and communication applications are a substantial portion of the 68020 market. These applications are concerned with the performance of the processor alone, not a system. Second, it is implied that general purpose computer systems are not capable of running without wait states. This is a dangerous underestimation of the capability of the various system implementors using the 68020. The notion of an off-chip cache is mentioned but then discarded. I do not believe that it is possible to dispose of the various system solutions available to the system designers, many of which are already being used on 68000 systems. Third, reviewing the performance figures cited in the note there are several very significant discrepancies. Assuming that we use the figure of 3-5x performance of a VAX-11/780 to an 8MHz 68000 then I don't understand how the table below was generated. > "VAX MIPS" > > CPU 100ns 200ns 300ns > ---------------------------------------------------------- > 8MHz 68000 0.14-0.23 0.14-0.23 0.14-0.23 > 16MHz 68020* 0.42-0.70 0.30-0.50 0.24-0.40 > 16MHz 68020** 0.56-0.90 0.46-0.76 0.40-0.66 > ---------------------------------------------------------- > VAX-11/780 0.7-1.0 > VAX-11/785 1.0-1.5 > ---------------------------------------------------------- > * I-cache disabled > ** 100% I-cache hit ratio If we start with the presumption that 3-5x is valid then I assume we use 4x for the 11/780 to 68000 comparison. This would give us the following performance figures: CPU 100ns 200ns 300ns ---------------------------------------------------------- 8MHz 68000 0.18-0.25 0.18-0.25 0.18-0.25 ---------------------------------------------------------- VAX-11/780 0.7-1.0 VAX-11/785 1.0-1.5 ---------------------------------------------------------- Using the 68000-68020 relationship shown in the performance tables in IEEE MICRO in terms of 68000 performance. CPU 100ns 200ns 300ns ---------------------------------------------------------- 8MHz 68000 0.6 (1x) 0.6 (1x) 0.6 (1x) 16MHz 68020* 2.1 (3.5x) 1.5 (2.5x) 1.3 (2.2x) 16MHz 68020** 2.7 (4.5x) 2.3 (3.7x) 2.0 (3.3x) ---------------------------------------------------------- When the two tables are combined, it shows a respectable cost/performance ratio. If a microprocessor based product performs at or above the level of a VAX, that seems significant. CPU 100ns 200ns 300ns ---------------------------------------------------------- 8MHz 68000 0.18-0.25 0.18-0.25 0.18-0.25 16MHz 68020* 0.61-0.88 0.44-0.63 0.39-0.55 16MHz 68020** 0.79-1.13 0.65-0.93 0.58-0.83 ---------------------------------------------------------- ------------------------- VAX-11/780 0.7-1.0 VAX-11/785 1.0-1.5 ------------------------- Fourth, the 68020 was designed to operate at 16MHz worst case, just as there are currently 10 and 12.5MHz 68000 and 68010's available now, it is not unrealistic to anticipate higher frequency 68020's in the years to come. In conclusion, we designed a chip which is a processor. We did not design a system. When we describe the performance of our chip it is only appropriate to describe it in terms of a processor. There are too many variables that can make a comprehensible evaluation impossible (i.e. compiler technology, system configuration, system access times, etc.) that don't have anything to do directly with the performance "capability" of the 68020. For this reason, I feel that this method of performance evaluation is not only appropriate, but essential. P.S. I would be interested in seeing a performance evaluation of the VLSI-based VAX and microVAX processors as well as the systems, are there any public descriptions of these? Doug MacGregor