[Info-vax] OT: Computing Experience, What brought you to VMS?

[already5chosen at yahoo.com]

On Sunday, February 16, 2014 8:17:23 PM UTC+2, glen herrmannsfeldt wrote:
> already5chosen at yahoo.com wrote:
> 
> (snip)
> 
> > VAX has 64-bit floating point implemented in hardware. 
> > And numeric properties of VAX FP formats are quite reasonable 
> > even by today's standards. So, VAX 11/750 is not a fast number 
> > cruncher, but has nothing to be ashamed of on precision side 
> > of things.
> 
> The 11/730 had H-float as standard, it was an optional extra
> for most other models, including the 11/750.
> 

H_floating is quad-precision. Nice to have, but not really necessary for ordinary uses.

In the statement above I had in mind G_floating - the most universally useful among VAX floating-point formats.
I was under impression that G_floating was available on all VAX models. Is it incorrect?

> 
> 
> > On the other hand, CDC floating point arithmetic had reputation 
> > for very bad numeric properties. Was it fixed in Cyber 200 series?
> 
> Makes sense if you consider what Cray did on the later machines.
> There are many algorithms where close is good enough. If you are
> a little careful, the deviations will average out, and many of those
> need a fast processor.

I disagree.
Of course, fast, precise and consistent is the best. But if I would be pushed to give up on one of the three I'd rather give up on the 2nd, then on the first, but not on the 3rd.

> 
> Remember the Cray machine with non-commutative multiply?
>

No, I'm too young to remember.

> 
> And the Cray-1 approximate reciprocal?
> 
> -- glen