[TUHS] long lived programs (was Re: RIP John Backus

[tfb@tfeb.org (Tim Bradshaw)]

On 22 Mar 2018, at 21:05, Bakul Shah <bakul at bitblocks.com> wrote:
> 
> I was thinking about a similar issue after reading Bradshaw's
> message about FORTRAN programs being critical to his country's
> security. What happens in 50-100 years when such programs have
> been in use for a long time but none of the original authors
> may be alive? The world may have moved on to newer languages
> and there may be very few people who study "ancient" computer
> languages and even they won't have in-depth experience to
> understand the nuances & traps of these languages well enough.
> No guarantee that FORTRAN will be in much use then! Will it be
> like in science fiction where ancient spaceships continue
> working but no one knows what to do when they break?

My experience of large systems like this is that this isn't how they work at all.  The program I deal with (which is around 5 million lines naively (counting a lot of stuff which probably is not source but is in the source tree)) is looked after by probably several hundred people.  It's been through several major changes in its essential guts and in the next ten years or so it will be entirely replaced by a new version of itself to deal with scaling problems inherent in the current implementation.  We get a new machine every few years onto which it needs to be ported, and those machines have not all been just faster versions of the previous one, and will probably never be so.

What it doesn't do is to just sit there as some sacred artifact which no-one understands, and it's unlikely ever to do so.  The requirements for it to become like that would be at least that the technology of large-scale computers was entirely stable, compilers, libraries and operating systems had become entirely stable and people had stopped caring about making it do what it does better.  None of those things seems very likely to me.

(Just to be clear: this thing isn't simulating bombs: it's forecasting the weather.)

--tim

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