Help reading a 9 track tape

[Paul Koning]

> On Aug 2, 2021, at 8:45 PM, Chuck Guzis via cctech <cctech at classiccmp.org> wrote:
> 
> On 8/2/21 8:11 AM, James Liu via cctech wrote:
>> Thanks for feedback and offers to assist.  
> 
> Happy to contirubte.
> 
>> For some background, Tini Veltman developed Schoonship in the 1960's
>> at CERN on the CDC 6600.  My understanding is that he more or less
>> insisted on coding in assembly since he thought FORTRAN or other high
>> level languages would just get in the way and slow things down.  The
>> code was maintained by Veltman and Strubbe well into the 1970's, but
>> its future was held back by being so closely tied to CDC hardware.
> 
> Which CDC FORTRAN?  RUN, maybe--but FTN extended was pretty darned good
> in optimizing and scheduling instructions. A lot of work went into that one.

He did say "in the 1960s" so it may have been an early one without the high quality optimizations that grew over time.

> As a matter of fact, when we COMPASS scriveners came up against a nasty
> loop that we wanted to optimize for the 6600, one approach was to code
> it in FORTRAN to see what the compiler would do with it and then work
> from there.   Some of the optimizations were quite startling,
> particularly with the "UO" option selected.
> 
> If you've never written and hand-optimized 6600 code, it could be a
> daunting task.

So I learned, having to do it on a 6400 -- which is quite a lot easier.  But I learned a lot from reading the OS source code, stuff like the analog of memcpy that used both the boolean and shift units for transfer operations so it could do two of them one cycle apart.

	paul