Here's a pretty cool article I came across doing a Google search on IBM's VM OS. It's a couple years old, but it gives you a pretty good idea of what's been going on in Big Iron land for the last few years. I like this line:

"His test system finally ran out of resources at 41,400 Linux images." :grin:

Posted on 2003-03-09 13:39:43 by S/390

Interesting read. :)

BTW: how many MIPS is a single (but not virtualized) 390 CPU capable of?
Posted on 2003-03-09 17:06:01 by Maverick
Hi Mav,

The new top-of the-line Z900 tops out at something like 3,250 MIPS (I've got the exact figures at work, I'll try to remember to post them tomorrow). But that's a really big, really expensive box. You can also get small machines, down to the 60 MIPS range, or even smaller.

But the real power of the mainframe is in it's channels. Each channel is in fact a small computer that operates on its own, independent of the CPU. A big box can have hundreds of channels. The program issues a single SIO (Start IO) instruction, that points to a "channel program", and the channel takes over while the CPU continues to execute instructions for another program (remember, the mainframe was designed from the ground up as a multi-tasking box). A typical channel program might be SEEK to a specific disk cylinder, SEARCH one of the tracks at that cylinder for a specific record, and READ that record. After all the data is transfered, the channel issues an interrupt, and the original program can resume.

Posted on 2003-03-09 22:36:32 by S/390

Hi S/390 :)
interesting.. do you have a link to a good page that describes the architecture in more detail, please?
Posted on 2003-03-10 03:43:50 by Maverick
Sure, here's a link to the "Principles of Operation" on the IBM Bookserver site. This is the "traditional" System/360/370/390 box with 32 bit "logical" words:

And here's a link to the same thing for the new 64 bit "logical" word z series machines:

The logical word is the size of registers, etc. and isn't related to the "physical" word that the hardware fetches. For example, the old 360/30 was an 8 bit physical word machine, so it had to do 4 strorage accesses for each 32 bit word! The 360/40 was a 16 bit machine, so it needed 2 accesses for each word. The 360/50 was a true 32 bit machine. The 360/65 was a 64 bit machine, so it fetched 2 words in a single access. If you only used 1 of the 2 words, the other was in the "cache" ready to go if you needed it next. This is also cool because some control words like the PSW (sorta like the x86 (E)IP) and the CCWs (Channel Command Words used to build the channel programs discussed above) are 64 bits.

Posted on 2003-03-10 16:45:54 by S/390

Very interesting stuff.. thank you pal. :)
Posted on 2003-03-10 17:18:55 by Maverick
wasen't IBM going to start offring linux on all of it's
mainframes as the standard O/S for these machines
I saw some place that thay ported the kernal and gcc themselves and moved all of the gnu utills over to there
mainframes not just there servers
Posted on 2003-03-11 01:39:37 by rob.rice
Well, I don't know about the "standard OS". Remember, this is technology with a 40 year history, and a huge installed base. There are billions of lines of custom COBOL, Fortran, RPG, PL/1, and Assembly code in production today, that depend on the OS. Not to mention hundreds of commercial packages.

I think OS/390 will continue to be the premier OS, especially for large systems, VSE will keep it's foot in the door on small systems, and VM will continue to have a following because of it's ability to provide multiple environments on a single box.

However, IBM has designed a couple models specifically for Linux. I'm not sure what the differences are between them and a "standard" S/390, but I'll look into it if you like.

Posted on 2003-03-11 20:06:00 by S/390
the way I understouded it VM seemed more like a hardware layer than an O/S
or maybe a software layer under the O/S
BUT may be I'm wrong

I think cray also has linux for it's mainframes

I don't think it matters what O/S is running for programs writen in COBOL, Fortran, RPG, PL/1 as long as thay are recompiled for that O/S or at least it shoulden't ( in theroy) unless the programmer pulls some trick or uses assembly code in the program

However, IBM has designed a couple models specifically for Linux. I'm not sure what the differences are between them and a "standard" S/390, but I'll look into it if you like.
yes please do
Posted on 2003-03-11 23:43:50 by rob.rice
I gather if you are running a web site that takes millions of hits an hour that you don't even bother with small stuff like PCs, minis etc ... Mainframes have so much processing grunt that they can handle millions of connection an hour at processing rates that would make a PC wet itself.

I saw system 360 machine when I was a kid with tape drives, HDDs and core storage, fill it full of big modern technology and the capacity and speed would be awesome.

Posted on 2003-03-12 07:14:00 by hutch--
Hi Rob,

Sorry for the late reply, been swamped with "real" work the last few days. :)

1) Don't confuse Virtual Memory hardware with the Virtual Machine OS. Virtual Memory is supported by all the IBM OSes. The Virtual Machine OS is 100% software.

2) I agree that it may be pretty easy to port some programs to Linux. But while Linux is a good, stable OS, the fact is that it doesn't offer anywhere near the number of services as OS/390, or the other mainframe OSes. Things like the VSAM file system come to mind for example. Or "extensions" of the OS, like CICS. I'm not saying that these things couldn't be ported to Linux, just that they aren't yet, as far as I know.

3) I did a little searching on Linux mainframe hardware and came up with this, for example:

It seema that there's very little difference between a "Linux box" and a "standard box", other than you're only "allowed" to run Linux apps on the Linux box. Looks like more of a marketing thing than a technical one...

Posted on 2003-03-15 22:37:42 by S/390

IBM has such a stronge commemtment to linux that thay may be working on the missing parts right now with the cost of linux thay can afford to extend it

yes I did look at IBMs z900 web page and thay call VM an OS and from the link you posted thay put VM on there big linux machines or may be it is an option thay wern't veary clear on that
Posted on 2003-03-16 13:46:38 by rob.rice