hancock4@[EMAIL PROTECTED]
wrote:
> 1) "HFP" and "BFP". It appears that BFP "Binary Floating Point" is a
> new instruction group. Could someone explain the difference to the
> original HFP? I thought everything was stored in binary, and hex was
> simply the external representation for us humans. Also, what are the
> advantages of BFP? (I am not trying to do anything, just curious
> about modern features.)
BFP is pretty much IEEE standard floating point, as most other
processors in use now use, and is required for Java.
For HFP, the original floating point format from S/360 carried
on to ESA/390 and Z, it is more than the external representation.
The representation of short (32 bit) HFP has six hex digits (stored
in 24 bits) of fraction, seven bits as a base 16 biased exponent,
and a sign bit. Among other differences, in HFP you can lose
precision multiplying by two.
> 2) Super computer work:
> From time to time IBM announces a new supercomputer for extremely
> "industrial strength" calculations. These days they seem to be many
> parallel processors of PC style architecture, not S/390.
> On alt.folklore.computers, there seems to be an attitude of disdain
> for using the S/390 mainframe for high powered number crunching. I'm
> not sure why; some say it is because of poor rounding, normalization
> or lack of "IEEE" compatibility, but the Pr of Op does cover all those
> issues. Indeed, "normalized" instructions have been around since
> System/360 days.
I believe it is mostly cost. Compare the price of a fast x86
or even x86-64 processor to a z/ machine. With x86-64 you
can buy a very large cluster of machines for the price of
one z/ machine.
> Our new Z9 seems to be extremely powerful. I would think a
> production machine such as that might be cheaper and just as powerful
> as a specially constructed machine.
Economy of scale. Yes compared to other specially constructed
machines, but if it can be done using off the shelf hardware
it can be much cheaper.
> If I understand the Pr of Op correctly, the standard "extended"
> floating point allows 128 bits, or about 31 digits of precision. That
> seems to be quite a bit. (That seems to date back to S/370 days 30
> years ago, has the precision been extended since then with newer
> machines?)
Actually, it dates back to the 360/85, and from there to S/370
except that DXR wasn't added until much later.
-- glen
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