Paravirtualization

In computing, paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar but not identical to that of the underlying hardware. This requires operating systems to be explicitly ported to run on top of the virtual machine monitor (VMM), which the owner of exclusive rights in a proprietary operating system may decline to allow for strategic purposes, but may enable the VMM itself to be simpler and for the virtual machines that run on it to achieve higher performance.

This is a new term for an old idea. IBM's VM operating system has offered such a facility for several decades. In the VM world, this is referred to as a "DIAGNOSE code", because it uses an instruction code used normally only by hardware maintenance software and thus undefined. IBM's Conversational Monitor System uses DIAGNOSE codes to call VM to request services. The Parallels Workstation operating system calls its equivalent a "hypercall". All are the same thing: a system call to the hypervisor below. Such calls require support in the "guest" operating system, which has to have hypervisor-specific code to make such calls.

For the rest of the Wikipedia entry on the above term, go here.

Pascal programming was made popular in the 1990's by Borland. Below is an old Turbo Pascal presentation.