cprice@mips.COM (Charlie Price) (06/15/88)
In article <491@daver.UUCP> daver@daver.UUCP (Dave Rand) writes: >In article <22050@amdcad.AMD.COM> tim@amdcad.AMD.COM (Tim Olson) writes: >> >> Am29000 (Video DRAM) >>MIPS 12.7 Native, 15.2 VAX MIPS >> Am29000 (Caches) >>MIPS 17.4 Native, 22.3 VAX MIPS > >I am confused. How can a risc machine have a higher "vax mips" than >native mips? MORE (not less) risc instructions are required to >do the same task, when compared to a vax. > >If you are saying that the 29000 is 22.3 TIMES FASTER than a vax, then >say that - what you have said is not reasonable. I cannot believe that >you can execute a vax instruction in 78% of the time of a native >instruction (17.4/22.3). > >This implies that, if you can execute a native instruction in 1 clock, that >you can execute a vax instruction (memory-to-memory add, for example), in >0.78 clocks! > >-- >Dave Rand >{pyramid|hoptoad|nsc|vsi1}!daver!daver First, an observation (and reminder): VAX 11/780 MIPS 0.5 Native, 1.0 VAX MIPS The "standard VAX MIP" comes from a machine that executes about 500,000 instructions/sec on the average. This is called a "1 MIP machine" because, as explained in this group, some early advertising wars compared the 11/780 as equal to an IBM 370 model that was a "1 MIP" machine. The "1 MIP" figure is just a convention. Maybe it really would be better if we could all switch our vocabulary to "VUP" (VAX Unit of Processing) a metric used inside DEC (probably more precisely than we use MIPS here!) Given the above information, if an instruction set does the same work as a 780 with fewer than twice the number of instructions executed then the native MIPS can be lower than standard VAX MIPS. Charlie Price cprice@mips.com -- {ames|decwrl}!mips!cprice MIPS Computer Systems / 930 Arques Ave. / Sunnyvale, CA 94086 / (408) 720-1700