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Virtual Machine Hardware 349


Metcalfe's Law Refuted
from above: pdp0x14 writes "Cnet News reports on a powerful refutation of Metcalfe's Law (that...

so a VM supervisor next to the hardware has to emulate a TLB for the virtual machines that it manages; this could be by having special unique address space (shadow) tables ... specific to the virtual address space it was managing. if the VM supervisor was running on a software-load, inverted table hardware, it would possibly have to buttign a unique address space identifier and do the correct stuff with tlb loads and invalidates.

Call for information on virtual tape formats 353
One matter-of-interpretation is that some DEC OS's (for example RT-11 prior to V5.5 or so) write the...

a VM supervisor only really needs to be aware of the next level virtual machine address spaces ... it shouldn't have to know that the supervisor running in the virtual machine ... for which it is managing virtual address spaces ... in turn is emulating virtual machines in those virtual address spaces.

Virtual Machine Hardware 351
John Savard one of the original uses of distributed development with the internal network (the internal network had more nodes than the arpanet-internet from just about the beginning to sometime around mid-85) http...

so on 370, the low-end machines had TLBs that only handled a single virtual address space at a time ... switching virtual address space pointer would always flush the TLB. the 370-168 was STO-buttociative (segment table origin, unique per virtual address space) with a 3bit identifier. It had seven slots to remember STO addresses ... and each TLB entry was either invalid, or buttociated with one of the seven (saved) STO addresses. If a new STO address was loaded that wasn't already in the TLB table, it would select one of the STO slots for replacement and invalidate all TLB entries with the corresponding STO-buttociative slot tag.

vm370 went thru somewhat similar evolution ... initially keeping only a single shadow table per virtual machine and each time the virtual machine changed its virtual page table pointer, it would invalidate all the page table entries in the shadow table. Later versions of vm370 would keep multiple shadow tables per virtual machine and effectively perform a Debt Management algorithm similar to that described for the 370-168 TLB.

At the same time, there was an evoluation of virtual machine microcode hardware buttists ... with awareness of running in virtual machine mode with shadow tables ... and on a page table entry miss ... would simulate the function of the VM supervisor ... checking to see if the corresponding address space table in the virtual machine space was valid and then translating it using the address space table in the VM supervisor (for that virtual machine) to resolve the page number for filling in the page table entry in the shadow table.

there is a special case for virtual machine microcode hardware buttists for pr-sm and lpars ... where the hypervisor microcode is providing a subset of the virtual machine function and the "virtual machine" storage is a dedicated section of contiguous memory. in this case, the TLB Debt Management hardware just has to be aware of which parbreastion it is operating on and adjust all (supposedly) real page numbers with the fixed address offset (aka starting address of that parbreastions fixed storage).

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Call for information on virtual tape formats 352
I first saw the TPC format in the DECUS tools used to copy sigtapes for distribution up the tape tree. (The tools at the time were BIGTPC for distribute now have been converted to TAP...


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Metcalfe's Law Refuted

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Decimal Exponent Floating like in JOSS 348