MVS is the ancestor of a modern operating system, z/OS, also capable of running on hercules, albeit with much more by way of hardware requirements (I wouldn't want to run it on a raspberry pi). IBM's licencing prohibits the installation of z/OS on anything other than IBM mainframe hardware, which in itself led to a bizarre situation where IBM, defender of open source projects and patent abuse decided to start abusing patents against an open source project
 - http://www.youtube.com/watch?v=GRW4iPhCDSM&feature=relat...
 - http://arstechnica.com/information-technology/2010/04/ibm-br...
There were also the FLEX-ES systems that were Linux-based mainframe emulators running on Intel hardware. IBM sanctioned and allowed this for long enough for a number of companies (including mine) to buy them, then pulled the plug on the program and forced everyone to buy real mainframe hardware instead.
When I took an operating systems class a few years back, a comment the professor made about z/OS stuck in my mind. "z/OS is one of the few operating systems that can run a VM of itself with almost no overhead." He went on to mention that he had seen nested VMs on z/OS about twelve steps deep that ran without noticeable delay.
Since he said this, I've always wanted to ask someone with some experience with the OS whether or not this is a valid observation. Additionally, does z/OS act similar to a BSD jail, where the kernel itself is replicated to improve security? I've not been able to find a whole lot of free/open documentation on the operating system.
I wouldn't say that there's no overhead, but the structure of z series mainframes is completely different to any midrange architecture. Everything is designed to be virtualised, parallelised and incredibly redundant. Hard disk fails? No problem, carry on as normal. Motherboard failure? No problem, carry on as normal.
z/OS doesn't have a kernel, it has what's called the nucleus. Effectively, the physical system is divided into LPARS, which then provide in effect highly scalable virtualised systems. There's then further isolation through about 3 different methods IIRC (for example, each subsystem - analogous to a long running process has it's own addressable memory) to the point where everything can be completely isolated, so it's very different to a jail, slightly like something like Xen (but only slightly).
The security model on z/OS is completely different to Unix/Windows because the entire architecture is completely different (for example, z/OS uses a block-based disk operating system as opposed to a byte stream filesystem, meaning there's no such thing as files in the Unix sense on z/OS - outside of USS which is beyond the scope of this comment).
Under z series LPAR virtualisation each LPAR runs it's own OS with it's own allocated resources. It's about as separate as you can get. You'd never use virtualisation that way on midrange as you cheat to get more VMs into less space, but on z series you need to absolutely guarantee access to a resource when needed, so you partition the systems up accordingly.
Please note, if anyone knows better than this please correct me, as I say I'm more on the security side than operator so I might be wrong in a couple of places.
 - http://en.wikipedia.org/wiki/Logical_partition_(virtual_comp...
 - http://publib.boulder.ibm.com/infocenter/zos/basics/index.js...
Data making it's way through the device chain was nothing for a 3 MIPS processor with 64 MB of internal memory and 3MB IO to handle.
As far as IPL's were concerned, it was more common for the controllers to be IPL'd than it was for the processor. Because of heat and cooling issues, nobody ever wanted to shutdown the processing system or even let those boards deviate much from their operational temperature. Bad things always happened when they powered down and cooled off. Always.
Raspberry PI is better compared to a PDP-11, a VAX, or a Data General (Soul of a New Machine).
 - http://simh.trailing-edge.com/
XOX for the win!
My sincerest apologies to whomever this offended, it was absolutely not my intention!
"I'm a total a nerd and have been all my life I've been on HN for over 2yrs and I can honestly say there's nowhere else on the entire internet where people make comments that even come close to how nerdy yours does!"
That being said it still isn't that funny and it doesn't really add anything to the conversation, but likely wouldn't have offended anyone either.
EDIT: forget to mention kudos for apologizing and not whining about downvotes like most people seem to now.
But you're right, "That is the nerdiest thing I have ever heard in my life" would probably have been better. And yet, still not constructive in any way. At least this little altercation is constructive, at least for my attitude!
GP2X = open-source handheld gaming platform from a few years back.
EDSAC = one of the first programmable computers ever made, upon which the very first video game was programmed: XOX, a game of naughts and crosses. (This fact was referred to culturally in the movie "Wargames"..)
Having an EDSAC in my pocket was definitely a Nerd moment, and you are forgiven. It is extremely Nerdy.
Now: Want to Play a Game (of XOX)? ;)
I agree it doesn't belong here, but I don't get how it's cyberbullying or anything close to it. Unless you think calling someone 'nerdy' is a grave insult around here, which I also don't really think is the case.
PS: Still, to give an idea of why Manframes where considered such IO beasts a high end PC's IO is about ~1000x as fast (HDMI is 10.2 Gbit/s + USB + Gigabit Ethernet etc), but it's got ~1,000,000x the processing power.
There is just something very cool about handling something on the order of 10^5 fully ACID transactions per second, while still allowing real time database querying and on-the-fly hardware failure tolerance.
Mainframes are obsolete systems which decades ago all the worlds infrastructure relied on, today they are obsolete systems that all the worlds infrastructure relies on and tomorrow they will be ....
Up to 4x I/O channels running at 3MB/second for the mainframe would be considered pretty good for small (4 kiB to 16 kiB) file operations on almost all microSD cards today.
Brilliant, I've wondered for a while now what my boss has meant every time he's told me that they're IPL'ing the mainframe and that I'll have to remount my exported NFS shares.
Oh, and one bit wrong and you can start all over again... the scary thing is that once you've done it often enough you start to remember the sequences the same way you remember how to play a piece on the piano, in your muscle memory.
I imagine a little cluster of these things in my house :)
Additionally, the SDD in your 901 isn't just a hunk of flash - it contains additional logic that will perform Wear Leveling on the physical flash modules, resulting in more write cycles before you see a failure. (Higher-capacity thumb drives also have wear levelers to fight against the OS's propensity to always allocate data sectors in the same order, but they're a different variety than those found in SSDs, from what I've read)
That said my NSLU2 has been running Debian for years on a 2GB USB stick, swap included. There are a few Linux knobs you can turn to reduce writes a bit.
FAQ says it can not.
just kidding...but I can't help but wonder if even the people who are kids now will realize this stuff isn't from the nineteenth century... I mean, just look at the device you're reading this on :) We've come a long, long way.