This document discusses different types and levels of virtualization. It begins by defining virtualization as the creation of virtual versions of servers, operating systems, storage, and other resources. It then discusses the main types and levels of virtualization: 1. Hardware virtualization creates virtual machines that have access to real hardware via a hypervisor. This can be done at the instruction set architecture level, hardware abstraction layer level, or operating system level. 2. Paravirtualization requires modifying guest operating systems. It replaces non-virtualizable instructions with hypercalls. 3. Host-based virtualization installs a virtualization layer on the host operating system rather than running directly on hardware. The document also covers

1. Cloud Computing

2. Unit III
Virtualization

3. Virtualization
• Virtualization is the "creation of a virtual (rather than actual) version of
something, such as a server, a desktop, a storage device, an operating system
or network resources".
• Virtualization is a technique, which allows to share single physical instance
of an application or resource among multiple organizations or tenants
(customers). It does by assigning a logical name to a physical storage and
providing a pointer to that physical resource when demanded.
• Creation of a virtual machine over existing operating system and hardware is
known as Hardware Virtualization. A Virtual machine provides an
environment that is logically separated from the underlying hardware.
• The machine on which the virtual machine is going to create is known
as Host Machine and that virtual machine is referred as a Guest Machine

4. • This virtual machine is managed by a software or firmware, which is
known as hypervisor.
• Firmware's are generally a type of software used to control
hardware devices.
• Firmware is a software program or set of instructions programmed
on a hardware device. It provides the necessary instructions for how
the device communicates with the other computer hardware.
• Firmware is typically stored in the flash ROM of a hardware device.

6. Implementation Levels of
Virtualization
• Virtualization is implemented at different levels by resembling specific
structures into analogous software that appears to work as the same
way as physical structure. The levels upon which virtualization is
implemented is shown in figure

7. Virtualization at ISA
(Instruction Set Architecture) level
• Virtualization is implemented at ISA (Instruction Set Architecture) level by
transforming physical architecture of system’s instruction set into software
completely. The host machine is a physical platform containing various
components, such as process, memory, Input/output (I/O) devices, and
buses. The VMM installs the guest systems on this machine. The emulator
gets the instructions from the guest systems to process and execute. The
emulator transforms those instructions into native instruction set, which are
run on host machine’s hardware. The instructions include both the I/O-
specific ones and the processor-oriented instructions. For an emulator to be
efficacious, it has to imitate all tasks that a real computer could perform.
• The instructions should be interpreted before being executed. And therefore
the system with ISA level of virtualization shows poor performance.

8. Virtualization at HAL
(hardware abstraction layer) level
• This level helps perform virtualization at the hardware level. It uses a
bare hypervisor for its functioning. This level helps form the virtual
machine and manages the hardware through virtualization.
• It enables virtualization of each hardware component such as I/O
devices, processors, memory, etc.
• The virtualization at the HAL (Hardware Abstraction Layer) is the
most common technique, which is used in computers on x86
platforms that increases the efficiency of virtual machine to handle
various tasks
• The working of virtualization technique wants catching the execution
of privileged instructions by virtual machine, which passes these
instructions to VMM to be handled properly.

9. • This is necessary because of the possible existence of multiple virtual
machines, each having its own OS that could issue separate privileged
instructions. Execution of privileged instructions needed complete
attention of CPU. If, this is not managed properly by VMM, and it will
raise an exception, which will result in system crash.
• Trapping and forwarding the instructions to VMM, helps in managing
the system suitably, and thereby avoiding different risks.

10. Virtualization at OS (operating
system) level
• To overcome redundancy and time consumption issues, virtualization
at the operating system level is implemented. This kind of technique
includes the sharing of both the OS and hardware. The physical
machine is being separated from logical structure (virtual system) by
separate virtualization layer, which could be compared with VMMs in
functions. This layer is built on the top of the OS, which could enable
the user to access to multiple machines, which is isolated from
others and is running independently.

11. Virtualization at library level
• Programming the applications in more systems needs a widespread
list of Application Program Interfaces (APIs) to be disseminated by
implementing several libraries at user level.
• These APIs are used to save users from miniature details involved
with programming related to the OS and facilitate the programmers
to write programs more easily.
• At the user level library operation, a different virtual environment is
provided, in that kind of perception. This virtual environment is
created above the OS layer, which could expose a different class of
binary interfaces together.
• This type of virtualization is well-defined as an implementation of
various set of ABIs (Application Binary Interfaces). The APIs are being
implemented with the help of the base system and execute the
function of ABI/API emulation.

12. Virtualization at application level
• Application-level virtualization comes when you wish to virtualize only
an application. It does not virtualize an entire platform or environment.
• On an operating system, applications work as one process. Hence it is
also known as process-level virtualization.
• It is generally useful when running virtual machines with high-level
languages. Here, the application sits on top of the virtualization layer,
which is above the application program.
• The application program is, in turn, residing in the operating system.
• Programs written in high-level languages and compiled for an
application-level virtual machine can run fluently here.

13. • The user level programs and the operating systems are executed on
applications, which behave like real machines. The memory mapped
I/O processing technique or I/O mapped input/output processing is
used to deal with hardware .Thus, an application might be taken
simply as a block of instructions, which are being executed on a
machine. The Java Virtual Machine (JVM) carried a new aspect to
virtualization and it is known as application level virtualization.
• The main concept after this type of virtualization is to produce a
virtual machine that works distinctly at the application level and
functions in a way similar as a normal machine. We can run our
applications on those virtual machines as if we are running our
applications on physical machines.

14. Virtualization Structures/Tools and
Mechanisms

15. Before virtualization, the operating system manages the hardware.
After virtualization, a virtualization layer is inserted between the
hardware and the OS. In such a case, the virtualization layer is
responsible for converting portions of the real hardware into virtual
hardware. Depending on the position of the virtualization layer, there are
several classes of VM architectures, namely
• Hypervisor architecture,
• Paravirtualization
• host-based virtualization.
• The hypervisor is also known as the VMM (Virtual Machine Monitor).
They both perform the same virtualization operations.

16. Hypervisor and Xen Architecture
• Depending on the functionality, a hypervisor can assume a micro-kernel
architecture like the Microsoft Hyper-V. Or it can assume a monolithic
hypervisor architecture like the VMware ESX for server virtualization.
• A micro-kernel hypervisor includes only the basic and unchanging
functions (such as physical memory management and processor
scheduling). The device drivers and other changeable components are
outside the hypervisor.
• A monolithic hypervisor implements all the aforementioned functions,
including those of the device drivers. Therefore, the size of the hypervisor
code of a micro-kernel hypervisor is smaller than that of a monolithic
hypervisor.

17. Xen Architecture
• Xen is an open source hypervisor program developed by Cambridge
University.
• Xen is a microkernel hypervisor, which separates the policy from the
mechanism. It implements all the mechanisms, leaving the policy to
be handled by Domain 0. Xen does not include any device drivers
natively. It just provides a mechanism by which a guest OS can have
direct access to the physical devices.

18. • Like other virtualization systems, many guest OSes can run on top of
the hypervisor. The guest OS (privileged guest OS), which has control
ability, is called Domain 0, and the others are called Domain U. It is
first loaded when Xen boots without any file system drivers being
available.Domain 0 is designed to access hardware directly and
manage devices.
• Therefore, one of the responsibilities of Domain 0 is to allocate and
map hardware resources for the guest domains (the Domain U
domains).

19. Binary Translation with Full
Virtualization
• Depending on implementation technologies, hardware virtualization can
be classified into two categories: full virtualization and host-based
virtualization.
Full Virtualization
• With full virtualization, noncritical instructions run on the hardware
directly while critical instructions are discovered and replaced with traps
into the VMM to be emulated by software. Both the hypervisor and VMM
approaches are considered full virtualization. Noncritical instructions do
not control hardware or threaten the security of the system, but critical
instructions do. Therefore, running noncritical instructions on hardware
not only can promote efficiency, but also can ensure system security.

22. Host-Based Virtualization
• An alternative VM architecture is to install a virtualization layer on
top of the host OS. This host OS is still responsible for managing the
hardware. The guest OSes are installed and run on top of the
virtualization layer. Dedicated applications may run on the VMs.
Certainly, some other applications can also run with the host OS
directly. This host based architecture has some distinct advantages,
as enumerated next. First, the user can install this VM architecture
without modifying the host OS. Second, the host-based approach
appeals to many host machine configurations.

23. Para-Virtualization
• It needs to modify the guest operating systems. A para-virtualized VM
provides special APIs requiring substantial OS modifications in user
applications. Performance degradation is a critical issue of a virtualized
system. Figure illustrates the concept of a para-virtualized VM
architecture. The guest OS are para-virtualized. They are assisted by an
intelligent compiler to replace the non virtualizable OS instructions by
hypercalls. The traditional x86 processor offers four instruction execution
rings: Rings 0, 1, 2, and 3. The lower the ring number, the higher the
privilege of instruction being executed. The OS is responsible for
managing the hardware and the privileged instructions to execute at Ring
0, while user-level applications run at Ring 3

26. Types of Hypervisors
• A hypervisor, also known as a virtual machine monitor or VMM. The
hypervisor is a piece of software that allows us to build and run virtual
machines which are abbreviated as VMs.
• A hypervisor allows a single host computer to support multiple virtual
machines (VMs) by sharing resources including memory and processing.
• The hypervisor is a hardware virtualization technique that allows
multiple guest operating systems (OS) to run on a single host system at
the same time.
Types of Hypervisor –
There are two types of hypervisors:
1. Type 1 (Native Hypervisor or Bare metal hypervisor)
2. Type 2 (Hosted Hypervisor).

28. Type 1 (Native Hypervisor or Bare metal
hypervisor)
• The hypervisor runs directly on the underlying host system. It is also
known as a “Native Hypervisor” or “Bare metal hypervisor”. It does
not require any base server operating system. It has direct access to
hardware resources. Examples of Type 1 hypervisors include VMware
ESXi, Citrix XenServer, and Microsoft Hyper-V hypervisor.
• They are usually faster and more powerful than hosted hypervisors.
For these purposes, the majority of enterprise businesses opt for
bare-metal hypervisors for their data center computing requirements.

29. Pros & Cons of Type-1 Hypervisor:
• Pros: Such kinds of hypervisors are very efficient because they have
direct access to the physical hardware resources(like Cpu, Memory,
Network, and Physical storage). This causes the empowerment of the
security because there is nothing any kind of the third party resource
so that attacker couldn’t compromise with anything.
• Cons: One problem with Type-1 hypervisors is that they usually need
a dedicated separate machine to perform their operation and to
instruct different VMs and control the host hardware resources.

30. TYPE-2 Hypervisor:
• A Host operating system runs on the underlying host system. It is also
known as ‘Hosted Hypervisor”. Such kind of hypervisors doesn’t run
directly over the underlying hardware rather they run as an
application in a Host system(physical machine). Basically, the
software is installed on an operating system. Hypervisor asks the
operating system to make hardware calls. An example of a Type 2
hypervisor includes VMware Player or Parallels Desktop. Hosted
hypervisors are often found on endpoints like PCs.

31. Pros & Cons of Type-2 Hypervisor:
• Pros: Such kind of hypervisors allows quick and easy access to a guest
Operating System alongside the host machine running. These
hypervisors usually come with additional useful features for guest
machines. Such tools enhance the coordination between the host
machine and the guest machine.
• Cons: Here there is no direct access to the physical hardware
resources so the efficiency of these hypervisors lags in performance
as compared to the type-1 hypervisors, and potential security risks
are also there an attacker can compromise the security weakness if
there is access to the host operating system so he can also access the
guest operating system.

32. Thank you