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virtual 36067 support in cp67


IBMWatson autobiographythoughts on
This came up before, but I remain curious as to what people think of the autobiography Tom Watson, Jr wrote about himself, his...

the early cp67 releases just provided support for "regular" 360 virtual machines .... i.e. virtual machines with standard 360 real memory ... and did not support virtual machines with address relocation hardware architecture found in 360-67 (aka you could run cp67 on a real 360-67, but running cp67 in a virtual machine wasn't supported).

in recent post about networking, bitnet, & earn

there was a reference to and old posting that included email about the formation of earn

the author of the subject email had many years earlier been on buttignment to the cambridge science center

and was responsible for adding support in cp67 for virtual machines with address relocation hardware architecture. basically the 360-67 control registers had to be simulated ... recent reference:

TSO replacement
from melinda's By the time we celebrated VM-370's tenth birthday at SHARE 59 in...

as well as "virtual" segment and page tables. Virtual address space segment and page tables in the memory of the virtual machine would have address translation from a virtual machine's virtual address space (3rd level addresses) to some address within the memory of the virtual machine (which was also virtual, aka 2nd level addresses).

Considering the real memory as "1st level addresses", and the virtual machine addresses as "2nd level addresses", then a virtual machines, virtual address space tables specified "3rd level addresses". Simulating virtual machine address space relocation hardware required building *shadow* segment and page tables (for the 3rd level addresses). The virtual address space tables in the virtual machine translated from 3rd level addresses to 2nd level addresses. The *shadow* segment and page tables, translated from 3rd level addresses directly to (real machine) 1st level addresses. whenever the virtual machine thought it was switching to its virtual address space tables (in the memory of the virtual machine), the cp67 simulation would actually switch to the *shadow* tables (that gave the 3rd level to 1st level address translation).

misc. past posts mentioning virtual address space simulation with *shadow* tables

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