From mboxrd@z Thu Jan 1 00:00:00 1970 From: paul.winalski@gmail.com (Paul Winalski) Date: Mon, 26 Mar 2018 12:19:44 -0400 Subject: [TUHS] long lived programs (was Re: RIP John Backus In-Reply-To: References: <284abf07f5b9d442caf233a8017a8cebb5518bbc@webmail.yaccman.com> Message-ID: On 3/26/18, Tim Bradshaw wrote: > On 23 Mar 2018, at 19:28, Bakul Shah wrote: > Retail banks are risk-averse so they like to avoid the risks associated with > porting the thing to new platforms. And since there's no development most > of the developers leave. > > And then ten or twenty years later you have this arcane thing which no-one > understands any more running on a platform which is falling off the end of > support. > After grad school (1978) one of my first job interviews was for a job as system manager for an insurance company. Their data center took the "don't risk porting software" to an extreme. As new technology came out they bought it, but only to run new applications. Existing applications were never ported and continued to run on their existing hardware. Their machine room looked like a computer museum. They had two IBM 1400s (one in use; one was cannabilized for parts to keep the active machine going), two System/360 model 50s, with a drum and a 2321 data cell drive. Their only modern hardware was a System/370 model 158. Operating systems seem to have taken one of two policies regarding legacy programs. IBM's OS and DEC's VMS emphasized backwards compatibility--new features mustn't break existing applications. VMS software developers called the philosophy of strict backward compatibility "The Promise" and took it very seriously. Unix, on the other hand, has always struck me as being less concerned with backward compatibility and more about innovation and experimentation. I think the assumption with Unix is that you have the sources for your programs, so you can recompile or modify them to keep up with incompatible changes. This is fine for research and HPTC environments, but it doesn't fly in corporate data centers, where even a simple recompile means that the new version of the application has to undergo expensive qualification testing before it can be put into production. Which philosophy regarding backwards compatibility is better? It depends on your target audience. -Paul W.