Modern Operating Systems by Herbert Bos ...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Showing 102 out of 1137
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 102
SEC. 1.7
‘‘virtual machine monitor’’ requires more keystrokes than people are prepared to
put up with now. Note that many authors use the terms interchangeably though.
Type 1 hypervisor
Host operating system
Excel Word Mplayer Apollon
Machine simulator
Guest OS
Host OS
OS process
Host operating system
Type 2 hypervisor
Guest OS
OS process
Figure 1-29.
(a) A type 1 hypervisor. (b) A pure type 2 hypervisor. (c) A practi-
cal type 2 hypervisor.
While no one disputes the attractiveness of virtual machines today, the problem
then was implementation.
In order to run virtual machine software on a computer,
its CPU must be virtualizable (Popek and Goldberg, 1974).
In a nutshell, here is
the problem. When an operating system running on a virtual machine (in user
mode) executes a privileged instruction, such as modifying the PSW or doing I/O,
it is essential that the hardware trap to the virtual-machine monitor so the instruc-
tion can be emulated in software. On some CPUs—notably the Pentium, its prede-
cessors, and its clones—attempts to execute privileged instructions in user mode
are just ignored. This property made it impossible to have virtual machines on this
hardware, which explains the lack of interest in the x86 world. Of course, there
were interpreters for the Pentium, such as
, that ran on the Pentium, but with
a performance loss of one to two orders of magnitude, they were not useful for ser-
ious work.
This situation changed as a result of several academic research projects in the
1990s and early years of this millennium, notably Disco at Stanford (Bugnion et
al., 1997) and Xen at Cambridge University (Barham et al., 2003).
These research
papers led to several commercial products (e.g., VMware Workstation and Xen)
and a revival of interest in virtual machines.
Besides VMware and Xen, popular
hypervisors today include KVM (for the Linux kernel), VirtualBox (by Oracle),
and Hyper-V (by Microsoft).
Some of these early research projects improved the performance over inter-
preters like
by translating blocks of code on the fly, storing them in an inter-
nal cache, and then reusing them if they were executed again. This improved the
performance considerably, and led to what we will call
machine simulators
, as
shown in Fig. 1-29(b). However, although this technique, known as
binary trans-
, helped improve matters, the resulting systems, while good enough to pub-
lish papers about in academic conferences, were still not fast enough to use in
commercial environments where performance matters a lot.

Ace your assessments! Get Better Grades
Browse thousands of Study Materials & Solutions from your Favorite Schools
Concordia University
Great resource for chem class. Had all the past labs and assignments
Leland P.
Santa Clara University
Introducing Study Plan
Using AI Tools to Help you understand and remember your course concepts better and faster than any other resource.
Find the best videos to learn every concept in that course from Youtube and Tiktok without searching.
Save All Relavent Videos & Materials and access anytime and anywhere
Prepare Smart and Guarantee better grades

Students also viewed documents