On Friday, 09/19/2003 at 07:22 EST, Richard Troth <[EMAIL PROTECTED]> wrote: > Kris ... you hit it ... > > > As far as I understand VMWare, it is not an emulator, actually, > > but a type of hypervisor that uses many dirty tricks to provide a > > virtual PC on top of a host PC. That's why it runs close to the > > host processor's speed for most basic execution. It's when > > privileges instructions need to be executed that it gets hit > > (the x86 architecture doesn't make virtualization easy). > > So in that sense it has similarities to z/VM. > > Right. > Virtualization means that the "guest" runs on the underlying hardware > until some obvious exception kicks it into emulation mode (such as > a privileged operation, I/O or the like). Just as virtual memory > is physically held in real storage when operated upon, so a virtual > machine is executed by the real CPU, until there is a "fault".
I just wanted to emphasise that z/VM does not intercept all privileged operations. Whenever possible, the hardware (SIE) handles it, with CP never being the wiser. SIE continues to be enhanced so that CP overhead is minimized. (Before SIE, VM/SP did, indeed, emulate privops.) Alan Altmark Sr. Software Engineer IBM z/VM Development
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