Ysean
"It would be nice if we knew, or had access to, [IBM] MIPS measurement methodology & data sets. Then we could run the data sets with comparable methodology across the multitude of systems out there & see just exactly how well these expensive machines run."
Oh, no need for this. In terms of CPU power, IBM Mainframes are dog slow. You need eight Nehalem-EX cpus to match the largest IBM Mainframe which has 64 cpus.
The largest IBM Mainframe gives 28.000 MIPS, that is 437MIPS per cpu. An 8-socket Nehalem-EX gives 3.200 MIPS, that is 400MIPS per Nehalem-EX (when you use the IBM Mainframe software emulator Turbohercules).
http://en.wikipedia.org/wiki/TurboHercules#Performance
But remember that software emulation is a factor 5-10x slower than running native code. So if you could port Mainframe code to x86, you would not get 400MIPS per Nehalem-EX, but instead 2.000 - 10.000MIPS. So 8-socket Nehalem-EX machine would give 16.000-32.000MIPS, which is in par with the largest IBM Mainframe.
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Also, another source, an independent Linux expert that ported Linux to IBM Mainframe gives the rule of thumb: 1 MIPS == 4MHz x86. But that number is from 2003 when Pentium4 ruled the earth. The new Nehalem and Sandybridge are at least 4 times faster, clock for clock, than the Pentium4. So the new rule of thumb would be 1 MIPS == 1 MHz x86. So if you have 2GHz eight core Nehalem-EX, then you have 16GHz in aggregate MHz. That corresponds to 16.000MIPS when running native code. In this case, again you only need a few Nehalem-EX to match the largest IBM Mainframe. "Debunking the IBM Mainframe myth":
http://www.mail-archive.com/linux-390@vm.marist.edu/msg18587.html
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So we have two independent sources that claim that only a few Nehalem-EX are needed to match the largest IBM Mainframe which has 64 cpus.
In fact, you can emulate a Mainframe on your laptop:
http://blogs.sun.com/jsavit/entry/once_again_mainframe_linux_vs
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Anyway, I dont see the new z11 with 50.000MIPS being much faster. Then you simply need 16 Nehalem-EX to match that machine. That is hilarious. But of course, Mainframes have good I/O, not good CPUs.
For reliability, there is a large market for the software emulator TurboHercules which IBM is suing now (despite IBM has promised not to sue open source projects that use IBM's released 511 patents!). If the Mainframes are that reliable, then why is IBM afraid of a backup solution such as TurboHercules? Read about the case TurboHercules vs IBM here. Start from the bottom. It turns out that Groklaw is IBM biased and censore all IBM critizicism. Do not trust Groklaw.
http://ibmvshercules.com/