Post ApwrTS1mz5QUJC2YF6 by jhamby@chaos.social
 (DIR) More posts by jhamby@chaos.social
 (DIR) Post #ApwrT1Pxv5ipmM8yg4 by jhamby@chaos.social
       2025-01-10T08:50:01Z
       
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       From a tech standpoint, the cool thing about IBM mainframes in general is they're really good at running VMs and VMs inside of VMs (there's a top-level hypervisor layer called "PR/SM" that you get for free, then you typically run z/VM or KVM).
       
 (DIR) Post #ApwrT2YrfUR1KFJbBg by jhamby@chaos.social
       2025-01-10T08:52:37Z
       
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       Here's Dave Plummer from Dave's Garage visiting the IBM mainframe HQ in Rochester, NY.https://youtu.be/ouAG4vXFORc?si=oLyl54gVVHdWfgIV
       
 (DIR) Post #ApwrT3puvZfZHQIjPE by jhamby@chaos.social
       2025-01-10T08:55:08Z
       
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       Here's Ars Technica's 2023 story on mainframes.https://arstechnica.com/information-technology/2023/07/the-ibm-mainframe-how-it-runs-and-why-it-survives/The OS is EBCDIC (and ASCII and all the other code pages and Unicodes and such). When you run Linux, it's just like any other Linux but it's big-endian, which is sadly rare these days (you can shake out bugs by testing on both endians).There's an IBM mainframe you can get a free time-limited account on the mainframe at Marist, the college in Poughkeepsie, NY, where IBM's mainframe engineering is.https://linuxone.cloud.marist.edu/
       
 (DIR) Post #ApwrTCCXpKWTDuwumm by jhamby@chaos.social
       2025-01-10T08:55:50Z
       
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       That's a LinuxONE account. You can also get free z/OS access by going through the Z Xplore self-taught classes in all the mainframe tech. That course is fascinating af, just because so much of it is so alien, but also highly optimized.
       
 (DIR) Post #ApwrTK3Gdhr5ZSfcR6 by jhamby@chaos.social
       2025-01-10T08:57:54Z
       
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       The z16 is innovative, relative to earlier models, for having an onboard AI coprocessor, and having the 32 MB L2 cache per core that gets dynamically shared around to be used as L3 and L4 caches across cores, chips, and boards within the system.
       
 (DIR) Post #ApwrTS1mz5QUJC2YF6 by jhamby@chaos.social
       2025-01-10T09:25:47Z
       
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       Typically you buy an IBM mainframe because you're a giant bank, insurance company, airline, etc. and that's what you've been using, and you want to run all your batch and/or interactive mainframe workloads as you've been doing them.They're DRM'd to Hell and back. Typically most of the cores are off and the customer enables the ones they've paid for. You can negotiate a cheaper price if you get the ones that can't run z/OS or any other IBM OS but "only" Linux, plus you can offload Java to it.
       
 (DIR) Post #ApwrTfLPTRqTboJu88 by jhamby@chaos.social
       2025-01-10T09:29:04Z
       
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       IBM mainframe CPUs are the CISCiest of CISC processors. BTW, they also use POWER CPUs in the network storage arrays, which I'll get back to shortly.Not only can a 64-bit mainframe run 31-bit (don't ask), and the original 24-bit address space (with the 32nd bit to distinguish between them) address space modules, but it's a mix of all three address space lengths. 16 MB virtual memory seemed huge in the 1960s, especially after you had VMs that could have their own 16 MB. Then 31-bit, then 64.