On Monday 10 June 2002 03:52 pm, Rick Troth wrote: > What David Rock said. > And I don't think VMware is at all to blame. > I *suspect* that virtualization of Pentium is hard to do. > zSeries has more than three decades of hardware and software > adjusting for each other to do virtualization very efficiently.
The Intel chips virtualize in what's called "virtual 8086 mode". Basically what this means is that most of the non-privileged instructions execute at full native speed, but any privileged instruction (including all I/O) must be trapped and software-emulated. The "virtualization" term is a bit of a misnomer, because they aren't really doing microcode the way S/390 does. Intel is able to select a subset of its instructions that are "safe" to allow to execute natively even inside an environment that is nominally restricted. For example, "ADD AX,BX" simply adds together the contents of two registers; there aren't any memory management issues, setting of processor control bits, etc., so this is an intrinsically safe instruction. They do some trickery with memory addressing as well, using the memory management features introduced originally in the 80386. This is what can be done in *hardware* by Intel chips; the rest of VMWare is all software. I'm actually very impressed with the performance of VMWare on the machines where I've run it; if you have enough RAM, its "insertion loss" is reasonable especially since most PCs have CPU cycles to burn anyway. But it doesn't compete against z/VM, really, through no fault of either VMWare or Intel. They are different tools meant for a different purpose. Scott -- -----------------------+------------------------------------------------------ Scott Courtney | "I don't mind Microsoft making money. I mind them [EMAIL PROTECTED] | having a bad operating system." -- Linus Torvalds http://www.4th.com/ | ("The Rebel Code," NY Times, 21 February 1999)
