[Info-vax] clock problems with OpenVMS x86 on VirtualBox

[gah4]

On Monday, May 15, 2023 at 5:15:41 AM UTC-7, Dan Cross wrote:
> In article <8b6c6dbd-5dc4-41aa... at googlegroups.com>, 
> gah4 <ga... at u.washington.edu> wrote: 
> >[snip]
> >In the case of virtual machines, each one will have its own CPU timer, 
> >but only one TOD clock. STCK is not a privileged instruction, so programs 
> >(or OS) see the host clock.

> This would seem to violate Popek and Goldberg's virtualization 
> criteria; how is that squared? 
 
IBM was either lucky or smart, in the design of S/370, except for that one.

As well as I know, it mostly wasn't a problem until Y2K testing.  Who would
want a machine with the clock wrong on purpose? 

It might have changed later, as not much pre ESA/390 hardware was still
running by Y2K.  The favorite IBM method when a feature changes, is to put
in a control register bit that allows the new or old operation.

Wondering about some of those, I found this one:

https://www.vmware.com/files/pdf/techpaper/Timekeeping-In-VirtualMachines.pdf

which is the VMware description of how they virtualize clocks.