Don't Know Much About Mainframes, So I'm Intrigued...

July 7, 2009 3:54 PM

What is a modern mainframe computer? IANAP

So I randomly overheard some discussions about modern mainframe computing... and with all the "cloud computing" hype.. I'm sorta wondering what people mean nowadays when they say they work on a "mainframe" and what the most common work on mainframes is currently? Am I mistaken in thinking that mainframes mostly run nearly-obsolete COBOL programs for ancient financial systems? I assume so... so where can I brush up on what the "latest" is in mainframe software? Is there a vibrant mainframe developer community out there...? I assume it's all IBM -- but are there other developers for mainframe software?

posted by mhh5 to computers & internet (15 comments total)

IBM still sells quite a lot of mainframes these days. Some of them are used to run legacy programs, but a lot of them are used to run virtual machines, typically with Linux as the hosted operating system.

The mainframe hardware is reliable and fault-tolerant, which are useful features, and the underlying mainframe OS is uniquely suited to supervising virtual machines, as that's a very old and well developed mainframe feature.
posted by jedicus at 4:04 PM on July 7

Also, it's pretty much just IBM these days with over 90% marketshare. Fujitsu still makes an IBM-compatible mainframe, though. The last VAX hardware was sold off in 2005, but there are still legacy systems in operation.
posted by jedicus at 4:09 PM on July 7

IBM and Sun are the two main vendors that I'm aware of. I don't do any work with these types of systems, but I'm interested to see what else pops up.

I know that IBM just released the z10 mainframes, which are capable of running everything from z/OS (which is hugely backwards compatible -- back to the 60's -- with the System 3xx operating systems) to Linux and Solaris.

We have a Sun M8000 running a big PeopleSoft/Oracle install. It, obviously, runs on Solaris.
posted by SpecialK at 4:09 PM on July 7

Mainframe isn't as specific a term as you might think - a Sun M8000 is a mainframe in everything but name because it runs Solaris. I would only consider the direct modern descendants of old mainframes to still hold the title - IBM systems running OS/360 descendants (OS/390) and z-series machines.

The wikipedia article on the current mainframe computer market seems reasonably accurate. IBM & Fujitsu as mentioned, Unisys still maintains their systems though I'm not sure if anyone still buys new ones, HP sells NonStop systems that came from Tandem.

But for the most part it's IBM big iron, some of which is now running fairly modern stuff like virtual machine hypervisors, Linux and WebSphere.
posted by GuyZero at 4:19 PM on July 7

as an example of what kinds of apps mainframes run these days, I once taught a course in Java performance tuning at a credit reporting agency. They did all their dev on standard desktop machines running NT (at the time) but they deployed on an early version of WebSphere for z/OS. How they got to that situation I don't know, but at least some mainframes are hosting web services-based backends for all sorts of systems. It's dinosaurs with lasers on their heads.
posted by GuyZero at 4:22 PM on July 7 [2 favorites]

so where does ComputerAssociates or CA fit into this ecosystem? They develop software for mainframes, but IBM sells most of the hardware AND software... so how do these other guys even get installed?

And thanks for the answers, hivemind!
posted by mhh5 at 4:23 PM on July 7

Same way CA sells software for desktops. Don't forget that CA is the undertaker/zombie master of the software world - software goes there to die and generate maintenance revenue. It's a pretty typical third-party ecosystem play - they're not any different from Quest Software in the PC world and other third-party vendors. Even IBM can't do everything.
posted by GuyZero at 4:27 PM on July 7

software goes there to die and generate maintenance revenue

Sorry, I didn't make my actual point - some of CA's products date to when mainframes were fresh and new. A lot of their stuff is ooooooooooooooold.
posted by GuyZero at 4:27 PM on July 7

There are many things that common PC-type servers just can't do that "big iron" can. You can dynamically adjust resource allocations, such as configuring how physical resources are partitioned into virtual machines, i.e. 'n' instances of linux running simultaneously. Consequently, you can add or remove CPUs, RAM, mass storage, etc. while they are running without rebooting or powering down. In most cases you can even replace a damaged power supply without any downtime because they all have multiple redundant units. In essence, when you need something that just cannot be shut down no matter what, you have to turn away from commodity hardware that everybody is familiar with.
posted by Rhomboid at 4:28 PM on July 7 [1 favorite]

Consequently, you can add or remove CPUs, RAM, mass storage, etc. while they are running without rebooting or powering down.

While this is common for mainframe and uncommon in the PC world, you can get Sun systems and systems that run Windows that also support this.

In most cases you can even replace a damaged power supply without any downtime because they all have multiple redundant units.

You can buy 1U dell boxes that can do this. I think.

You can dynamically adjust resource allocations, such as configuring how physical resources are partitioned into virtual machines, i.e. 'n' instances of linux running simultaneously.

LPARs and such have been around for ages but VMware has brought this kind of capability to high-end PC server these days.

Rhomboid is right in general, but PCs have soaked up a lot of mainframe features in the last 20 years while mainframes have gotten better at being able to handle open systems and stuff like Java.

Then you have grids which have all of these features but typically require highly specialized runtime environments and don't run any OS known to man e.g. Hadoop, older stuff from Platform computing, in-house job systems developed by various wall st firms.
posted by GuyZero at 4:35 PM on July 7 [1 favorite]

Wikipedia's bit about the difference between a mainframe and a supercomputer is pretty good. A supercomputer is a big ass computer designed to run computationally-intensive applications, usually one at a time. A mainframe is a big ass computer that needs to do a whole lot of stuff that isn't necessary advanced, but where a lot has to happen all at once, like credit card processing. Lots of I/O.

The usual internet way to solve that problem is with lots and lots of cheap servers.
posted by yesno at 4:43 PM on July 7

So I can't find an actual commercial x86 server that offer hot-swappable CPUs. I thought windows supported it but I can't find a Dell or HP box that admits to it. I think HP might have an Itanium box that does it but now we're getting into less-than-mainframe more-than-PC territory. But they do run Windows.
posted by GuyZero at 4:46 PM on July 7

GuyZero, you'll need to be looking at Sun kit for that feature.
posted by SpecialK at 5:50 PM on July 7

Don't believe anyone who tells you mainframes are faster than PCs by any measurement. That's marketing. Mainframes are all about reliability.

There are PCs (and Sun Unix servers) that offer mainframe-like reliability, and much better performance. But banks and such have decades of experience and millions of lines of code written for mainframes, and they really don't care about performance (even a 386 could handle a thousand transactions per second). So why would they switch?

An easy way to play around with mainframes is to use the Hercules emulator. Only very old versions of IBM's mainframe operating systems are available for free.
posted by miyabo at 6:04 PM on July 7

"In most cases you can even replace a damaged power supply without any downtime because they all have multiple redundant units.

You can buy 1U dell boxes that can do this. I think."

Yeah, Intel's new modular server has this feature (it has three redundant power supplies) as well.
posted by HopperFan at 8:34 PM on July 7