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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 533
legacy support for multiple decades of backward compatibility. Over
the years, it had introduced four main modes of operations (real, pro-
tected, v8086, and system management), each of which enabled in
different ways the hardware’s segmentation model, paging mechan-
isms, protection rings, and security features (such as call gates).
x86 machines had diverse peripherals
Although there were only
two major x86 processor vendors, the personal computers of the time
could contain an enormous variety of add-in cards and devices, each
with their own vendor-specific device drivers. Virtualizing all these
peripherals was infeasible. This had dual implications: it applied to
both the front end (the virtual hardware exposed in the virtual ma-
chines) and the back end (the real hardware that the hypervisor need-
ed to be able to control) of peripherals.
Need for a simple user experience
Classic hypervisors were in-
stalled in the factory, similar to the firmware found in today’s com-
puters. Since VMware was a startup, its users would have to add the
hypervisors to existing systems after the fact. VMware needed a soft-
ware delivery model with a simple installation experience to encour-
age adoption.
7.12.4 VMware Workstation: Solution Overview
This section describes at a high level how VMware Workstation addressed the
challenges mentioned in the previous section.
VMware Workstation is a type 2 hypervisor that consists of distinct modules.
One important module is the VMM, which is responsible for executing the virtual
machine’s instructions. A second important module is the VMX, which interacts
with the host operating system.
The section covers first how the VMM solves the nonvirtualizability of the x86
architecture. Then, we describe the operating system-centric strategy used by the
designers throughout the development phase. After that, we describe the design of
the virtual hardware platform, which addresses one-half of the peripheral diversity
challenge. Finally, we discuss the role of the host operating system in VMware
Workstation, and in particular the interaction between the VMM and VMX compo-
Virtualizing the x86 Architecture
The VMM runs the actual virtual machine; it enables it to make forward
progress. A VMM built for a virtualizable architecture uses a technique known as
trap-and-emulate to execute the virtual machine’s instruction sequence directly, but

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