[Info-vax] VMS on Raspberry Pi 5

[Jake Hamby (Solid State Jake)]

On Thursday, November 16, 2023 at 5:36:21 AM UTC-8, Scott Dorsey wrote:
> Ahem A Rivet's Shot <ste... at eircom.net> wrote: 
> > 
> > Yes they are popular with banks and the like because they *also* 
> >run their old OS-360 stuff without recompiling it, but to anyone who 
> >doesn't need that they are very expensive for little gain. Guess what many 
> >of their customers run in the RHEL environments - yep kubernetes and docker.
> The IBM systems are I/O machines. The CPU is just sitting there telling the 
> I/O controllers what to do and most of the real work is being done by other 
> hardware outside the CPU. So you can have incredibly high workloads and 
> huge transation rates with relatively slow CPUs. 

This was definitely the case 20 years ago. Today, IBM Z CPUs are quite interesting in their own right. Massive caches. The previous z15 CPU had four levels of cache, with a whopping 960 MB of L4 cache (eDRAM) per CPU drawer. The current z16 has a different architecture with 32 MB of L2 cache per core and an innovative cache design that allows any CPU to borrow cache RAM from other CPUs on the same die, different dies, or even different CPU drawers, dynamically creating arbitrarily large virtual L3 and L4 caches.

They're never going to beat x86, ARM, or POWER on raw per-core compute speed, but for the giant databases their customers run, with terabytes of RAM for caching and massive I/O throughput, mainframe CPUs are quite fast. They have SIMD for decimal floating-point (as well as binary FP and integer math) to accelerate COBOL, an embedded sorting engine for in-memory "DFSORT" acceleration (sort/merge/copy), an embedded zlib engine for fast compression, and now an embedded neural engine to enable running AI fraud detection models on every transaction.

IBM's sales pitch for running Linux on Z is that it's more power-efficient to have one or two mainframes than a much larger number of x86 blades doing the same thing. I'm sure that depends very much on workload. I should also mention z/VM, which is IBM's OS dedicated to running transactions (as opposed to z/OS, which is more general-purpose). z/VM is what all the airlines and Visa credit card transactions run on.

Finally, there's Parallel Sysplex, which is basically VMSclusters with dedicated hardware acceleration. Between that and all the redundancy and other RAS features, IBM can tout independent surveys showing 8 or even 9 9's of uptime! Their POWER10 servers don't look too shabby either.

https://techchannel.com/Trends/07/2023/ibm-z16-power10-high-reliability-servers

Of course you're paying a premium for all that custom engineering, but I think it's impressive, nonetheless.