robin wrote:
> "John W. Kennedy" <jwkenne@[EMAIL PROTECTED]
> wrote in message
> news:YCXxf.66$Fd6.27@[EMAIL PROTECTED]
>> robin wrote:
>>> "John W. Kennedy" <jwkenne@[EMAIL PROTECTED]
> wrote in message
>>> news:E1Uxf.1208$l03.452@[EMAIL PROTECTED]
>>>> hancock4@[EMAIL PROTECTED]
wrote:
>>>>> John W. Kennedy wrote:
>>>>>> It is very well known that the entire 360 FP feature could have
used
>>>>>> some input from numerical analysts; it's shot full of design
defects.
>>>>> Could you elaborate on those design defects?
>>>>>
>>>>> How did S/360 compare with its predecessor machines (ie 709x)
regarding
>>>>> those defects? What differences did competitors machines--those
>>>>> available in 1965--have compared to S/360 regarding these defects?
>>>> To start with, the S/360 word was four bits shorter than the 704
word.
>>>> This was, at least, a strategic error, because it meant that
/up/grading
>>>> to a 360 meant, in this area, a /down/grading in function.
>>> Yes and no. Double precision gave 28 extra bits.
>> The 704 family offered double precision, too; it was not fully
>> implemented in hardware, but the hardware assisted it, and the FORTRAN
>> compiler sup****ted it.
>
> It had to, in order to meet the standard.
There was no FORTRAN standard until long afterwards.
>>> But for most work, little difference between 36 bits and 32 bits.
>>> But that's no measure, anyhow. The appropriate measure is
>>> the number of mantissa bits and range of exponent.
>> They add up to the word size, one way or the other.
>
> Not relevant; what's im****tant is the breakdown --
> and in particular, the number of mantissa bits.
In order to make any sense of your argument, I can only assume that you
do not know what the words "relevant" and "mantissa" mean. Kindly look
them up.
>> In any case, the
>> S/360 had significantly fewer effective fraction bits (21) in single
>> precision than the 7094 (27).
> Leaving only 7 bits for the exponent. In other words, a reduced
> range of exponent, which the S/360 corrected.
Having trouble with subtraction, are we now?
>> In practice, a very, very large number of
>> FORTRAN programs had to be altered to use double precision where single
>> precision had once served.
> I do not recall receiving a single complaint of that category,
> even though the machine that we upgraded from used 31
> mantissa bits for scientific work.
Then you were doing unusually undemanding work; plenty of shops had
major problems.
> The S/360 was not copied in its entirety,
Problem state was.
> and even in those
> cases where it was not copied in its entirety, the
> original hex floating-point design was retained
> (without guard digit on double, with zero for underflow, etc)
I'm sure IBM spent all that money upgrading all those machines without
payment just for fun.
> Strange, we got along well with F.P.
> And both machines that we subsequently obtained used
> the original hex floating point (without guard digit, etc).
> It is clear that it was not the problem that you imagine.
It is clear that it wasn't a problem for /you/. (Or, alternatively, that
it /was/ a problem, but you didn't audit your results adequately.)
> So-called "clones" retained the hex model without guard
> digit on d.p. Strange, that.
> How come *they* did not get "many problems"?
You buy cheap imitations, you get cheap imitations.
> And if it was as bad as you claim, how come they
> never implemented something better?
They did. In 1967, and again, recently.
--
John W. Kennedy
"But now is a new thing which is very old--
that the rich make themselves richer and not poorer,
which is the true Gospel, for the poor's sake."
-- Charles Williams. "Judgement at Chelmsford"
|
