On Thu, 9 May 1996 07:07:30 -0700 Bruce Toback said: >Jeff Kell writes: >> Even IBM's >> VM/ESA which does emulate multiple virtual physical machines (albeit all >> IBM platforms) only allows them to co-exist, not co-operate. They made a >> really big deal not that long ago about "shared code segments" that multiple >> users could share, and elaborated on converting your code to localize all of >> your data references to your assigned "data area" (non-trivial). >VM is in a quite different class from MPE's code and data management. In MPE, >the code and data protection can be overridden by privileged programs. You >can't run an OS as a process under MPE without compromising system integrity. >The point of VM is that there must be no way that a program can tell that it's >being run in a virtual machine, even if the "program" is a privileged OS. Actually I wasn't referring to shared OS segments, though the points are very valid. VM is older than MPE :-) so I was really making references to my past dues-paying (blues-playing) days as a big blue systems programmer, a career I no longer care to pursue. Simple separation of code and data was quite an effort. "Re-entrant" (shareable) and "relocatable" (dynamic loading) code were the result of careful planning and tedious details back in the dark ages. Then along comes MPE with inherently re-entrant, relocatable, protected code and even has the gall to use programs and files as swap area! Geez, even a COBOL programmer can write shareable code now; such heresy! (OK, that's my quota of exclamation marks...) Jeff Kell <[log in to unmask]>