The IBM mainframe: How it runs and why it survives • Hacker News Board

Re: The IBM mainframe: How it runs and why it survives

#191

Post by nikau » Wed, Jul 26, 2023, 11:39 AM UTC

hinkley wrote: post #85

CraigJPerry wrote: post #4

The reason mainframe persists is it's a pretty slick development and deployment environment. A lot things you might cobble together as dependencies - like maybe a database or a message queue, or observability facilities or even deployment strategies like hot-hot deployments - they're all just built in to the platform. That means they're trivial to consume and they're fully supported by one vendor. It's like the world…

Most of this Cloud technology we like to go all atwitter about is a retread or a redesign of software that's been on mainframes for thirty years. The old farts must laugh themselves silly looking at us acting like we discovered a large white object orbiting the earth.

just you wait, one day google cloud pub/sub will have a queue pause feature!

Re: The IBM mainframe: How it runs and why it survives

#192

Post by nikau » Wed, Jul 26, 2023, 11:56 AM UTC

kmoser wrote: post #149

coleca wrote: post #33

Earlier quoted context omitted.

I've always heard that as "scheduled uptime" or "unscheduled outages". When I worked in a mainframe shop, they used to IPL (reboot) the mainframe every Sunday morning. That down time was never considered as part of the SLA.

Wow, even Windows boxes can run longer than a week without having to be rebooted. I figured a mainframe would be able to last almost indefinitely.

weekly reboots force the business to build their processes around the system being offline at the same time each week.

That way you don't have to try and organize downtime if maintenance is required, you know every sunday morning is available when needed.

Re: The IBM mainframe: How it runs and why it survives

#193

Post by larrik » Thu, Jul 27, 2023, 6:18 PM UTC

larrik wrote: post #79

I never worked on z/OS, but I did work on AS400 (Series I, or whatever it's called now). I think the main things missing is how much IBM really brings to the table here. > If one crashes or has to go down for maintenance, the other partitions are unaffected. Effectively, IBM often does that for you. The machine detects an issue, and calls IBM, who sends someone out (in my day it was immediately), and they fix it. The…

There was one other aspect of these machines I missed. They run forever.

We had a machine in there that by the time I left was running nonstop for 10 years. I was their only IT person for 5 of those years, and I basically visited them a few times a year to work on MSAccess reports, and never touched the server (I may have never even logged into it!). It just chugged along running their entire business with no maintenance.

Re: The IBM mainframe: How it runs and why it survives

#194

Post by kmoser » Sat, Jul 29, 2023, 7:09 PM UTC

nikau wrote: post #192

kmoser wrote: post #149

Earlier quoted context omitted.

Wow, even Windows boxes can run longer than a week without having to be rebooted. I figured a mainframe would be able to last almost indefinitely.

weekly reboots force the business to build their processes around the system being offline at the same time each week. That way you don't have to try and organize downtime if maintenance is required, you know every sunday morning is available when needed.

Not disagreeing, just commenting that I would have assumed that taking the entire system offline for a reboot on a weekly basis would be untenable from a business perspective. It seems at odds with the concept of all the redundancy built into mainframes to ensure high availability and uptimes. Given that many mainframe-based systems (e.g. airline reservations) generally need to be available 24/7/365, I would have assumed that while one part of the system is being rebooted, others are still available so the overall application can continue to run uninterrupted.

Re: The IBM mainframe: How it runs and why it survives

#195

Post by graycat » Tue, Aug 01, 2023, 7:00 PM UTC

neverartful wrote: post #174

graycat wrote: post #161

Ah, good to hear that the IBM mainframes are still around, are more powerful , and that the software for the old IBM mainframes will still run on the new mainframes. So, yup, JCL still works! An 3270 series video terminals with 24 lines of 80 characters each driven with CICS (customer information control system or some such) is still used. But I didn't see that (1) Rexx, often a good replacement for JCL, (2) XEDIT, a…

The latest incarnation of VM/370 is branded z/VM. Most of my hands-on mainframe work was with VM/CMS and I enjoyed using it.

For the software to schedule the fleet at FedEx, I wrote in PL/I on CP/67 (control program, i.e., virtual machine, for the IBM 360/67, with virtual memory) CMS (conversational monitor system, the user interface) on a 360/67 at National CSS time-sharing in Stamford, CT. Right, VM/370 was from CP/67! I wrote the code from my living room while teaching computer science at Georgetown U.

Then in Memphis, one evening used the code to develop a schedule for all planned 33 airplanes for all planned 90 US cities. The next day two representatives of BoD member and crucial investor General Dynamics went over the schedule carefully and announced to the BoD that "it is a little tight in a few places but it's flyable". Until that schedule, due to concerns of some BoD members, scheduling had been a show stopper. But with the schedule the BoD was pleased, crucial funding, equity and also counting loans on the planes, etc., $55+ million, was enabled, and FedEx was saved until the next such BoD crisis.

I solved the next such BoD crisis with the differential equation

y'(t) = k y(t) (b - y(t))

and for this one, for the computing for the data to draw a graph of the solution, used my new HP calculator I'd paid $400 for! There the BoD wanted some revenue projections.

NCSS was expensive, but I enjoyed using it AND PL/I! It didn't use 3270 communications and, instead, used asynchronous bits on a phone line and a portable terminal with heat sensitive paper in rolls. The terminal was from Execuport and supposed to be portable. Actually, it was delicate!

It is just staggering how far computing has come since then! Hardware, operating system software, APIs, user interfaces, communications, YES, but applied math, algorithms, and programming languages, not as much and, thus, seem more fundamental!!!!