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Comment by js8 | Hacker News Reader

I am a mainframe developer. It's sad that IBM isn't more open about z/OS and z/VM to hobbyists. I think it really hurts the mainframe in the long run.

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It's odd that we rarely hear from you guys on sites like this one. Why isn't there a VM that hosts JCL and which you can pass your own projects around on?

I wonder whether part of the problem might be that it's so awkward to replicate mainframe style init on desktop operating systems. Desktop OS init tends to be very pale against a mainframe. I'm working on a project related to this at the moment.

There is z/PDT for hobbyists although it will cost $4k for a basic setup. It's a emulator that runs on PC and have 3x OSS hercules-390 performance.

"although it will cost $4k for a basic setup"

It's a little more than my two monthly salaries (after tax) here in Czech Republic, and it's per year. I don't think I am nostalgic enough yet to pay for that. :-)

Anyway, thanks for info.

Is it a cultural thing? Is there a reason for this?

It's a legacy of the era when IBM ruled the roost. All of the mainframe vendors were like that.

There was an office space in the middle of our data center at my first big IT job. Only Unisys people were allowed to enter, and crossing the threshold into that room, or opening a Unisys cabinet was a serious offense.

I'd be secretive too! That "mainframe" was a $25,000 Xeon server with a mainframe emulator running on it. They had these sweet contracts where they would lease the server based on performance -- MIPS/mo.

The IBM mainframes are big power boxes with custom asics for i/o and lots of mumbo jumbo to make it sound magical.

I still think that in IBM's case this depends on what you mean by mainframe. Midrange systems (ie. AS/400) are power boxes and today even sold as such (IBM will sell you the hardware as "IBM Power system" with choice of AIX, OS/400 or Linux as OS). On the other hand I'm almost certain that System z CPUs are microcoded monstrosities that run z/Architecture machine code pretty much natively.

I've worked on the compilers for Z systems and on the z/PDT emulator that someone else mentioned. The processors they run are indeed monsters. The instruction set is especially interesting as you can see the transition from 24-31-64 bit. Messing around with the SAM (set address mode) instructions was always fun. They also have some interesting interruptable instructions that can move or compare up to 2GB of memory.

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