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

[Johnny Billquist]

On 2023-05-17 11:42, gah4 wrote:
> 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.

Thanks. That pretty much repeat what I've been writing in a number of 
posts now. I hope this can now be laid to rest.

   Johnny