This document discusses cloud computing, virtualization, and the Xen virtualization platform. It defines cloud computing as relying on shared computing resources over the internet rather than local servers. Virtualization allows multiple operating systems to run simultaneously on one machine through virtual machines. Xen is an open source virtualization platform that allows virtual machines called "domains" to run within a single physical machine managed by a hypervisor.

1. Submitted To: Mr. Prakash Kumar
Submitted by:
Nikita Gupta-10103526
Shubham Jain-10103489
Deadline Based Scheduling Technique for
Xen

2. What Is Cloud Computing?
• Cloud computing is a type of computing that relies on sharing
computing resources rather than having local servers or
personal devices to handle applications.
• In cloud computing, the word cloud (also phrased as "the cloud")
is used as a metaphor for "the Internet," so the phrase cloud
computing means "a type of Internet-based computing," where
different services such as servers, storage and applications are
delivered to an organization's computers and devices through
the Internet.
• Cloud computing is comparable to grid computing, a type of
computing where unused processing cycles of all computers in a
network are harnesses to solve problems too intensive for any
stand-alone machine.

3. What is Virtualization?
 Virtualization enables the running of multiple
operating systems on a single machine
 Each Virtual Machine (VM) is isolated and
protected from each other - Illusion of dedicated
physical machine
 Allows an abstraction of server workloads
 Motivation:
 Take advantage of idle machine time
 Easy to maintain and upgrade VMs

4. Xen Overview
 Developed at Cambridge University
 Allows multiple virtual machines within one physical
machine
 Open Source version available as option with Linux
Distributions
 Text-mode tools (but that is improving)
 Now also provided by XenSource (“Commercial Open
Source”)
 Free XenServer Express (complete distribution –
currently 32-bit only)
 Nice graphical tools

5. Domains
 Xen refers to virtual machines as domains
 The host OS runs in a special domain called
 domain-0 (Dom0)
 The guest OSes run in User Domains (DomUs).
 Domains have a domain number and a domain
name.
– Name is fixed; number varies (except for Dom0)
 But all Domains are guests of the Hypervisor

6. Virtualization at the OS Level
 Not based on host/guest paradigm
 Host runs a single OS kernel as its core and
exports OS functionality to each of the guests
 Guests must use the same OS as the host,
although different distributions of the same
system are allowed
 This distributed architecture eliminates system
calls between layers, which reduces CPU
usage overhead

7. Full Virtualization
 Hardware Virtual Machines
 VMWare, Xen HVM, KVM, Microsoft VM,
Parallels
 Runs unmodified guests
 Generally worst performance, but often acceptable
 Simulates bios, communicates with VMs through
ACPI emulation, BIOS emulation, sometimes
custom drivers
 Can sometimes virtualize across architectures,
although this is out of fashion.

8. Para-virtualization
 Hypervisor runs on the bare metal. Handles CPU scheduling
and memory compartmentalization.
 Dom0, a modified Linux Kernel, handles networking and
block storage for all guests.
 Dom0 is also privileged to manage the VMs on the system.
 DomU, or the guests OS, sends some requests straight to the
hypervisor, and others to the Dom0.
 Because the kernel knows its virtualized, features can be built
into it: hot connection/disconnection of resources, friendly
shutdown, serial console.
 Other para virtualization schemes: Sun Logical Domains,
VMware (sometimes)

9. The Para virtual Machine Model
 Also based on host/guest paradigm and uses a
virtual machine monitor
 But here the VMM actually modifies the guest
operating system’s code
 This is called porting
 Porting supports the VMM so it can utilize
privileged systems calls sparingly
 Xen and UML are examples of this model

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