Re: S/360

Hello,

multicsfan wrote:

<snip>

> The Cray-1 did not initially come with hardware divide, the divide was 
> done in software in the pipe.  Hardware divide was a $500K option which 
> was slower then the software divide ;)

No Cray-1 ever had hardware divide.
Floating point divide was always a reciprocal approximation,
followed by correcting multiplications.  A special 2-a.b instruction
applied part of the correction.

> Memory Parity was also a $500K option.  To check for memory errors the 
> idea was the Cray was so fast you could just run your program twice and 
> if you got the same answer there was no memory problem.

Serial #1 Cray-1 had no parity, Serial #2 was being built without parity
but was scrapped before completion.  Serials #3 and beyond
all had SECDED.  It added one clock to scalar memory fetch times,
raising it from 10 to 11 cp.

The only options ever available on the Cray-1 was how much memory
the customer wanted to buy.  (Modulo peripherals, of course.)
Most were sold with 1 MW, from 256 KW to 4 MW was
theoretically possible.

-- 
Cheers!

Dan Nagle
Purple Sage Computing Solutions, Inc.