Thompson, Steve wrote:
-----Original Message-----
<SNIP>
I keep seeing references to the "mainframe" processor is slower than
those used in other platforms.
Seriously, in an effort to compare processor power, IF one were to take
a COBOL program that would process 1000 records from a data base and
produce a report (let's say a payroll check register), which system
would process this in the least amount of elapsed time?
I ask this question in this fashion, because I know that Fujitsu has a
COBOL compiler that produces code that runs under Windows (I know,
because I have used it to do "batch" reporting at one time). I
understand that a similar compiler is available for other of the
platforms.
So, if we run the data base and applications system on a self-contained
system, which one will run with the lowest wall time?
This is the kind of benchmark that needs to be done. It, in my opinion,
is the only way to get close to a valid comparison.
Anyone else have any ideas?
[I still have the compiler, and I still have w/2K that I fixed it to
operate with if anyone would like to try to build a benchmark.]
Regards,
Steve Thompson
The "Mhz" rating of a zSeries CPU is slow than most of modern
processors. However that does not mean a computer using a slower
processor is slower than a computer using a faster process. That is
like saying just be cause the engine in one car runs at a higher RPM
makes it faster than a car whose engine that runs at a lower RPM. The
problem is that ignores the transmission and differential gearing.
In this case it ignores the CPU's various instruction sets. Say you
have two CPU that have different instruction sets. During a test it was
found that CPU#1 can execute a mixed set of it instruction at the rate
of 100 MIPS, and CPU#2 tested at 200 MIPS. Which is faster? You can't
tell. The problem is that CPU#2 may have a less efficient set of
instructions and you may have to execute 3 instructions to do the same
amount of work as CPU#1 does with 1 instruction.
I remember reading a article about the FLEX/ES software when it first
came out. They were taking about the difference in the two instruction
sets. The lowest instruction ratio was 1:2, zSeries to Intel, the
maximum was 1:1200 and the average was 1:17. So on average for every 1
zSeries instruction they had to execute 17 Intel instructions to do the
same work.
You also have the fact that some functions on zSeries are handled by the
hardware. Memory protection for one, zSeries hardware prevents one task
from getting to another tasks memory. I know on the Intel platform this
must be handled by the OS, so this is more instructions that the OS must
execute and more work done by the CPU.
IBM published a paper on the differences between zSeries and PowerPC and
the fact that zSeries CPU's are much better for SMP environments that
run varied workloads on a single computer. This deals with the way that
L2 cache works and what happens when you have a context switch. On the
distributed platforms L2 is not shared (pre-multi-core).
Some distributed OS's will actually hold up work if the CPU it was last
dispatched on is not available right now, this is to prevent the context
switch on another CPU.
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