Plain language explanation of whatever buzzes you in the daily IT world. It's my personal effort with two chapters ready.

1. This guide is born in a time at which
recruiters are being put at question
throughout social networks and I admit
myself, that I have been bashing them as
well. Truth is a lot of people enter the job
without really any basic knowledge of the
IT world and rely mainly on soft skills and
learning by doing. This often irritates
candidates and is not helping either sides in
the “war of talent”. Chapter 1 and 2
included…
IT
recruitement
for IT
recruiters
By the pray, for the hunters
Yakob Yakov

2. The IT recruiter’s guide to IT
Written by the victim of IT recruiters.
PREFACE
This guide is born in a time at which recruiters are being put at question throughout social networks and
I admit myself, that I have been bashing them as well. Truth is a lot of people enter the job without
really any basic knowledge of the IT world and rely mainly on soft skills and learning by doing. This often
irritates candidates and is not helping either sides in the “war of talent”.
Bashing recruiters for lack of knowledge is one thing, realizing that there is a real problem is another. If
this guide comes as help to anyone out there who is struggling with their day to day activities within IT
recruitment, I’d ask them, if they find a time to write a recommendation on my Linkedin Profile, which is
to be found at the bottom of this very same document.
The purpose of this guide is to fill the gaps of knowledge and lower the stress at work for all of the bees
in the industry, as well as to prepare newcomers for the challenges ahead. This guide is aimed at giving
you, the reader, the knowledge required to understand concepts of IT structures, IT technologies, job
descriptions, etc.

3. CHAPTER 1
What is an operating system? What is what in operating systems?
Everyone who uses a computer uses an operating system. It is what makes it possible for us to see
things on the screen. I take it back. It is what makes it possible for us to use the screen, and the mouse,
and the keyboard… Given that this definition is not fully correct, for the purposes of this chapter and
the audience it is aimed at.
The computer
The computer is a computational machine which uses input and output devices such as keyboards,
mouses, printers, network cards(that thing that makes the internet flow), monitors and many others.
The computer itself is very much like LEGO® blocks, though you need to have blocks from the same
series to make it work. Getting any deeper towards hardware wouldn’t bring you anything as a recruiter,
but further on there is a chapter dedicated to that.
Beware thought that your smartphone is a computational machine with all input devices integrated into
one. It has a processor, an operating system and an input device – the screen (Steve Jobs said, while
revealing the first iPhone that everyone has an input device for a smartphone – respectively our fingers).
The types of operating systems
This is a messy subject which confuses a lot of people outside the IT business, but the shit hits the fan
eventually when you realize you messed it up with a candidate.
The Windows operating system family
We all know them. These are as follows:
1. Windows for end-users: Obsolete versions: 3.1, 95, 98, 2000, XP; Live versions: 7, 8, 8.1, 10
2. Windows for enterprise aka Server : 2003, 2008, 2012, 2016
Windows for end users:
These are the versions of windows you and I would have on our computer for everyday use. Each one of
those has a patched version though which is directly relatable into the corporate environment in the so
called domains
Windows for enterprise:
This is a product line called Server or MS Server. It’s main feature are the so called domains. These are
databases containing information about users, computers and their rights and respective correlation
within the IT infrastructure. The domain is managed by Active Directory, also known as AD.

4. MS Server has several other features which include but are not limited to running different services and
acting as storage.
Throughout the years Microsoft has developed software which is dedicated to different tasks,
respectively runs services 24/7 on the server. The most popular ones:
- Microsoft Exchange: This is a mail server. What it does is – it acts as a post office for the
company it is set up for.
- Microsoft SQL Server: this is a a server system(take it software) that controls different databases
- Hyper-V: This is an integrated component of the Windows Server since 2008 which is used for
virtualization. Virtualization is discussed in a later chapter of this guide.
Linux and Unix
Linux and Unix are not the same thing, though they are very similar to each other. A Unix administrator
can be a Linux administrator and vice versa with a bit of reading. In a real world anybody who got their
hands on Unix has definitely worked with Linux.
Linux
There are several types of systems here, based on the core distributions, but these can be separated in
free(as in freedom) and commercial(as in “the company is paying for support”). All of them use the
Linux kernel, but are different and special in their details. We are going to have just a general overview
on those.
RedHat Enterprise Linux and Suse Linux Enterprise are examples of commercial Linux distributions.
Ubuntu is somewhere in the middle between commercial and not, as it offers professional services for
most of it’s solutions.
Debian, CentOS, Fedora and OpenSuse are free(as in free to download and try).
Often you will see in a job description RHEL/CentOS and you will be baffled. Well, the Linux distributions
have their own geeky way of separating each other – mainly the package management.
Unlike in Windows where you have to buy all the programs and download them from sources like Pirate
Bay (let’s be honest, most of you do that with movies, the Linux world has thought of a way to make
everything accessible thanks to repositories. Imagine those as big libraries full of software CD’s or files,
or whatever you wish. What the Linux world is divided with are the librarians – respectively the
software management tools.
The core systems SLES and RHEL use RPM packaging, but the free versions of those (CentOS, Fedora for
RedHat and OpenSuse for SLES) use RPM as well.
Debian based systems like Ubunt and Mint use deb packaging – a different library.

5. All of the above though – all of these systems are able to compile packages from source – something
recommended by most specialists. Compiling means taking a page of code and making it
executable(usable) and installing it on your computer.
Do not be afraid of Linux – it doesn’t bite.
Now that you are of who is who, it’s time for Chapter 2.
Chapter 2
Virtualization and clouds
Have you ever wondered why is this picture funny? Angry about not understanding it? Well,
virtualization and clouds go sometimes hand in hand, sometimes they don’t…
Virtualization
When I tried to explain to my girlfriend what is a virtual machine, I ended up telling her that it’s a logical
machine on top of a physical machine. She stared blank at me and went on. I have been thinking since
how to explain it to a non-IT person so I googled.
Kendrick Coleman came up with this:
Me: When you go to Subway, you know how they have those six-foot party subs?
Other Guy: Yea

6. Me: Well think of the 6ft party sub as your typical physical server. Every time you have to deploy a new
server, you have to order a six-foot party sub. When you go to subway, do you order a six-foot party sub
for lunch?
Other Guy: Well, no.
Me: Why not?
Other Guy: Because you would have a lot of wasted food.
Me: Exactly, so you would probably want five to 10 other people to help you eat that six-foot party sub
so nothing goes to waste. With today’s hardware, there are a lot of wasted resources when you have to
deploy a single physical server. Virtualization gives you the ability to have five-10 servers running on
that one physical server concurrently so your resources aren’t going to waste. Make sense?
There are multiple kinds of software used for virtualization of operating systems:
Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
AlphaV
M
EmuV
M
x86_64 Alpha
Windows,
Linux
OpenVMS, Tru64 UNIX
Propri
etary
bhyve
FreeB
SD
x86-64 x86-64 FreeBSD
FreeBSD, FreeNAS, pf
Sense, OpenBSD,GNU
/Linux, Windows[1]
BSD
Bochs
Kevin j
Lawton
Any x86, x86-64
Windows, Li
nux,FreeBS
D, Unix/X11,
Mac OS
9, OS
X,BeOS, Mo
rphOS,OS/2[
2][3]
Windows, Linux, DOS,
BSD, OS/2, Haiku
LGPL
Contain
ers, or
Zones
Sun
Micros
ystems
x86, x86-
64,SPARC(port
able: not tied to
hardware)
Same as host
Solaris 10,
Solaris
11, OpenSol
aris2009.06,
SmartOS
Solaris (8, 9, 10, 11),
SmartOS, Linux
(BrandZ)
CDDL

7. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
Cooper
ative
Linux(c
oLinux)
Dan
Aloni,
other
develo
pers
x86[4]
Same as host
Windows
2000, XP,
2003, Vista[4]
Linux
GPL
versio
n 2
CHARO
N
Stroma
sys
x86, x86_64
PDP-11, VAX,
Alpha, HP3000,
Sparc
Windows,
Linux
VMS, OpenVMS, Tru64
UNIX, MPE/iX, RSX-
11, RT11, RSTS,
Solaris, SunOS
Propri
etary
Denali
Univer
sity of
Washi
ngton
x86 x86 Denali Ilwaco, NetBSD ?
DOSBo
x
Peter
Veenst
ra,
Sjoerd,
commu
nity
help
Any x86, ARM
Linux,
Windows,
Mac OS
classic, OS
X, BeOS,
FreeBSD,
OpenBSD,
Solaris,QNX
, IRIX,
MorphOS,
AmigaOS,M
aemo,
Symbian
Internally emulated
DOS shell; classic PC
booter games,
unofficially Windows
1.0 to 98
GPL
DOSEM
U
Comm
unity
project
x86, x86-64 x86 Linux DOS
GPL
versio
n 2
FreeBS
D Jail
FreeB
SD
Any
runningFreeBS
D
Same as host FreeBSD FreeBSD, Linux ABI BSD

8. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
Guest
PC
Lismor
e
Softwa
re
Syste
ms
PowerPC x86 OS X DOS, Windows, Linux
Propri
etary
GXemu
l
Anders
Gavare
Any
ARM, MIPS, M88K,
PowerPC, SuperH
Unix-like
NetBSD, OpenBSD, Li
nux, Ultrix, Sprite
BSD
Hercule
s
Roger
Bowler
Any z/Architecture
Windows, Fr
eeBSD,Linu
x, OS X
Linux on z
Systems, z/OS, z/VM, z
/VSE,OS/360, DOS/36
0, DOS/VS, MVS, VM/3
70,TSS/370
QPL
Hyper-
V(2008)
Micros
oft
x86-64 +
hardware-
assisted
virtualization
(Intel VT-
x orAMD-V)
x86-64, x86 (up to
8 physical CPUs)
Windows
Server
2008 (R2)
w/Hyper-
Vrole,
Microsoft
Hyper-V
Server
supported drivers
for Windows
2000,Windows
2003, Windows
2008, Windows
XP, Windows
Vista, FreeBSD, Linux(
SUSE 10 released,
more announced)
Propri
etary
Hyper-
V(2012)
Micros
oft
x86-64 +
hardware-
assisted
virtualization
(Intel VT-
x orAMD-
V only for
RemoteFX)
x86-64, (up to 64
physical CPUs)
Windows
8/8.1 &Wind
ows Server
2012 (R2)
w/Hyper-
Vrole,
Microsoft
Hyper-V
Server
supported drivers
for Windows
NT,FreeBSD, Linux (S
USE 10, RHEL 6,Cent
OS 6)
Propri
etary
iCore
Virtual
Accoun
ts
iCore
Softwa
re
x86 x86
Windows
XP
Windows XP
Propri
etary

9. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
INTEG
RITY
Green
Hills
Softwa
re
ARM, x86,Pow
erPC
Same as host
Linux, Wind
ows
INTEGRITY
native, Linux, Android,
AUTOSAR, Windows (
on select platforms)
Propri
etary
Integrit
y
Virtual
Machin
es
Hewlet
t-
Packar
d
IA-64 IA-64 HP-UX
HP-UX, Windows,
Linux
(OpenVMSannounced)
Propri
etary
JPC
(Virtual
Machin
e)
Oxford
Univer
sity
Any running
the Java Virtual
Machine
x86
Java Virtual
Machine
DOS, Linux, Windows
up to 3.0
GPL
versio
n 2
KVM
Qumra
net,
now
Red
Hat
x86, x86-64,
IA-64, withx86
virtualization,
s390,
PowerPC[5]
Same as host
Linux,
FreeBSD,
illumos
FreeBSD, Linux,
Solaris, Windows, Plan
9
GPL
versio
n 2
Linux-
VServe
r
Comm
unity
Project
x86, x86-64,
IA-64, Alpha,
PowerPC
64,PA-
RISC 64,
SPARC64,
ARM, S/390,
SH/66, MIPS
Compatible Linux Linux variants
GPL
versio
n 2
LynxSe
cure
Lynux
Works
x86, Intel VT-
x, Intel VT-d
x86 No host OS
LynxOS, Linux,
Windows
Propri
etary
LXC
Comm
unity
project,
Canoni
x86, x86-64,
IA-64,
PowerPC 64,
SPARC64,
Same as host Linux Linux variants
GPL
versio
n 2

10. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
cal Ltd. Itanium, ARM
Mac-
on-
Linux
Mac-
on-
Linux
PowerPC PowerPC Linux
OS X, Mac OS 7.5.2 to
9.2.2, Linux
GPL
Mac-
on-Mac
Sebast
ian
Gregor
zyk
PowerPC PowerPC
OS X, up to
10.3
OS X, Mac OS 7.5.2 to
9.2.2, Linux
GPL
OKL4
Microvi
sor
Open
Kernel
Labs,
acquire
d
by Gen
eral
Dynam
ics
Corpor
ation
ARM, x86,
MIPS
ARM (v5, v6, v7)
(Paravirtualization),
ARMv7VE (HW
Virtualization)
No Host OS
Various OSes and
RTOSes
including Linux,Android
, QNX
Propri
etary
OpenV
Z
Comm
unity
project,
suppor
ted
bySWs
oft,
nowPa
rallels,
Inc.
x86, x86-64,
IA-64,
PowerPC 64,
SPARC64
Same as host Linux Linux variants GPL
Oracle
VM
Server
for x86
Oracle
Corpor
ation
x86, x86-
64,Intel VT-
x,AMD-V
x86, x86-64, Intel
VT-x, AMD-V
No host OS
Microsoft
Windows, Oracle
Linux, Red Hat
Enterprise
Linux, Solaris
Oracle
VM
Server
GPL;
Manag
er
propri

11. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
etary
Proxmo
x VE
Proxm
ox
x86-64, Intel
VT-x, AMD-V
x86, x86-64, Intel
VT-x, AMD-V
Debian
Based
Windows, Linux, Linux
variants, Solaris,
FreeBSD, OSx86 (as
FreeBSD), virtual
appliances, Netware,
OS/2, SCO,
BeOS,Haiku, Darwin
licenc
e
AGPL
v3
Oracle
VM
Server
for
SPARC
(LDoms
)
Oracle
Corpor
ation
UltraSPARC
T1,UltraSPAR
C T2,
UltraSPARC
T2+, SPARC
T3, SPARC T4
Compatible
Solaris 10,
Solaris 11
Supported: Solaris.
Without Oracle support:
Linux, FreeBSD
Propri
etary
OVPsi
m
OVP [3
]
x86
OR1K, MIPS32,
ARC600/700, ARM;
and public API
which enables
users to write
custom processor
models, RISC,
CISC, DSP, VLIW
all possible
Microsoft
Windows,
Linux
Depends on target
machine, for example
includes MIPS Malta
that runs Linux or SMP-
Linux; and includes
public API which
enables users to write
custom peripheral and
system models
Propri
etary,
Apach
e
2.0for
model
s
Parallel
s
Deskto
p for
Mac
Paralle
ls, Inc.
x86, Intel VT-x x86, x86-64 OS X x86
DOS, Windows,
Linux, OS X Server,
FreeBSD, OS/2,
eComStation,
Solaris,Haiku
Propri
etary
Parallel
s
Workst
ation
Paralle
ls, Inc.
x86, Intel VT-x x86
Windows,
Linux
Windows, Linux,
FreeBSD, OS/2,eCom
Station, DOS,
Solaris, Haiku
Propri
etary

12. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
PearPC
Sebast
ian
Biallas
x86, x86-64,
PowerPC
PowerPC
Windows,
Linux,OS X,
FreeBSD,
NetBSD
OS X, Darwin, Linux GPL
PikeOS
SYSG
O AG
PowerPC, x86,
ARM, MIPS,
SPARC,
SuperH
Same as host
No host OS,
Linux or
Windows as
dev.hosts
PikeOS native, Linux,
POSIX, AUTOSAR,
Android, RTEMS, OSE
K, ARINC
653APEX, ITRON
Propri
etary
PowerV
M
IBM
POWER4,PO
WER5,POWE
R6,POWER7,P
OWER8
POWER4/5/6/7/8,
x86 (PowerVM-
Lx86)
PowerVM
Firmware
Linux PowerPC,
x86; AIX, IBM i
Propri
etary
QEMU
Fabric
e
Bellard
, other
develo
pers
x86, x86-64,
IA-64,
PowerPC,
SPARC 32/64,
ARM, S/390,
MIPS
x86, x86-64, Alpha,
ARM, CRIS,
LM32, M68k,
MicroBlaze, MIPS,
OpenRisc32,
PowerPC, S/390,
SH4, SPARC
32/64, Unicore32,
Xtensa
Windows,
Linux,OS X,
Solaris,
FreeBSD,
OpenBSD,
BeOS
Changes regularly[6] GPL/L
GPL
QEMU
w/kqem
umodul
e
Fabric
e
Bellard
x86, x86-64 Same as host
Linux,
FreeBSD,
OpenBSD,
Solaris,
Windows
Changes regularly[6] GPL/L
GPL
QEMU
w/qvm8
6modul
e
Paul
Brook
x86 x86
Linux, NetB
SD,
Windows
Changes regularly GPL
QuickT
Transiti
ve
x86, x86-64, MIPS, PowerPC, Linux, OS X, Linux, OS X, Irix, Propri

13. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
ransit Corp. IA-64, POWER SPARC, x86 Solaris Solaris etary
RTSHy
perviso
r
Real-
Time
Syste
ms
GmbH
x86, x86-64 x86, x86-64 No host OS
Windows, Linux,
Windows Embedded,
QNX, RTOS-32,
VxWorks, OS-9, T-
Kernel
Propri
etary
ScaleM
PvSMP
Founda
tion
Scale
MP
x86, x86-64
Same as host, up
to 8,192 CPUs and
64 TB per VM
No host OS Linux
Propri
etary
SIMH
Bob
Supnik
, The
Compu
ter
History
Simula
tion
Project
Alpha, ARM,
HPPA, x86, IA-
64, x86-64,
M68K, MIPS,
MIPSel,
POWER, s390,
SPARC
Data
General Nova, Ecli
pse; Digital
Equipment
Corporation PDP-
1, PDP-4, PDP-
7, PDP-8, PDP-
9, PDP-10, PDP-
11, PDP-15, VAX;
GRI Corporation
GRI-
909; IBM 1401, 162
0, 1130, 7090/7094
, System/3;Interdat
a (Perkin-Elmer)
16b/32b systems;
Hewlett-Packard
2114, 2115, 2116,
2100,
21MX; Honeywell H
316/H516; MITS Alt
air
8800 with 8080and
Z80; Royal
McBee LGP-30,
LGP-21; Scientific
Data Systems SDS
940
BSD, Linux,
Solaris,
VMS,
Windows
Depends on target
machine, includes
NetBSD/VAX,
OpenBSD/VAX, VAX/V
MS,Unix v6, Unix
v7, TOPS-10, TOPS-
20, ITS
BSD-
like,
unique

14. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
Simics
Wind
River
x86, x86-64
8051, 68000, ARM
(v4, v5, v6, v7),
MIPS32, MIPS64,
Cavium cnMIPS,
Broadcom XLR
MIPS, Freescale
Power Architecture
32-bit and 64-bit
(e300, e500, e600,
e5500, e6500), IBM
Power Architecture
(POWER, PPC44x,
PPC46x, 47x),
SPARC v8 (LEON),
SPARC v9
(UltraSparc), x86
(from 80286 to
Sandy Bridge), x86-
64 (from Pentium4
to Sandy Bridge),
TI TMS320C64xx,
Renesas H8,
Renesas SH
Windows
32-bit and
64-bit, Linux
32-bit and
64-bit
Depends on target
machine, typically runs
unmodified software
stacks from the
corresponding real
target,
includingVxWorks,
VxWorks 653, OSE,
QNX, Linux, Solaris,
Windows,
FreeBSD, RTEMS,Tiny
OS, Wind River
Hypervisor, VMware
ESX, and others
Propri
etary
Sun
xVMSer
ver
Sun
Micros
ystems
x86-64,SPARC Same as host No host OS
Windows XP, 2003
Server (x86-64 only),
Linux, Solaris
GPL
versio
n 3
SVISTA
2004
Serenit
y
Syste
ms
Interna
tional
x86 x86
Windows,
OS/2, Linux
Windows, Linux, OS/2,
BSD
Propri
etary
TRANG
O
TRAN
GO
Virtual
Proces
sors,
Greno
ble,
France
ARM, XScale,
MIPS,
PowerPC
Paravirtualized AR
M, MIPS, PowerPC
No host OS,
Linux or
Windows as
dev. hosts
Linux, eCos, µC/OS-
II, WindowsCE,Nucleus
, VxWorks
Propri
etary

15. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
User
Mode
Linux
Jeff
Dike,
other
develo
pers
x86, x86-64,
PowerPC
Same as host Linux Linux
GPL
versio
n 2
Virtual
Box
Innotek
,
acquire
d
byOrac
le
Corpor
ation
x86, x86-
64,Intel VT-
x,AMD-V
x86, (x86-64 only
on VirtualBox 2 and
later with hardware
virtualization)
Windows,
Linux,OS
X x86,
Solaris,
FreeBSD,
eComStatio
n
DOS, Linux, OS X
Server,[7]
FreeBSD,Haik
u, OS/2, Solaris,
Syllable, Windows.
Also OpenBSD but only
with hardware
virtualisation indicating
inaccuracies in the
software memory
emulation layer
buttolerated by other
OS's.
GPL
versio
n 2;
full
versio
n with
extra
enterp
rise
featur
es is
propri
etary:
Virtual
Iron3.1
Virtual
Iron
Softwa
re,
Inc.,
acquire
d by
Oracle
x86 VT-x, x86-
64 AMD-V
x86, x86-64 No host OS Windows, Linux
Full
produc
t is
propri
etary,
a few
compo
nents
are
GPL
versio
n 2[8]
Virtual
PC2007
Conne
ctix &M
icrosoft
x86, x86-64 x86
Windows
Vista(Busine
ss,
Enterprise,
Ultimate),
XP Pro, XP
Tablet PC
Edition
DOS, Windows, OS/2,
Linux (SUSE,
Xubuntu), OpenSolaris
(Belenix)
Propri
etary
Windo
ws
Virtual
PC
Conne
ctix &M
icrosoft
x86, x86-64
with Intel VT-x
or AMD-V
x86 Windows 7
Windows XP, Windows
Vista, Windows 7,
Windows Server 2003,
Windows Server 2008
Propri
etary

16. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
Virtual
PC 7
for Mac
Conne
ctix &M
icrosoft
PowerPC x86 OS X Windows, OS/2, Linux
Propri
etary
VirtualL
ogixVL
X
Virtual
Logix
ARM, TI DSP
C6000,
x86,Intel VT-
x,Intel VT-d,
PowerPC
Same as host No host OS
Linux, Windows XP,
C5, VxWorks,
Nucleus,DSP/BIOS,
proprietary
Propri
etary
Virtual
Server
2005
R2
Conne
ctix &M
icrosoft
x86, x86-64 x86, x86-64
Windows
Server
2003, 2008,
XP
(Requires
IIS)
Windows NT, 2000,
2003, 2008, Linux (Red
Hat, SUSE, Ubuntu)
Propri
etary
Synops
ys
(CoWar
e)Virtua
l
Platfor
m
CoWar
e
x86, x86-64,
SPARC v9
Devices including
(multi) cores
from ARM, MIPS, P
owerPC, ToshibaM
eP, Renesas SH, T
exas
Instruments, Tensili
ca, ZSP
Windows,
Linux,
Solaris
Depends on guest
CPU;
includes: Linux(various
flavors), µITRON (vario
us flavors),Windows
CE, Symbian, more
Propri
etary
Virtuoz
zo
SWsoft
,
nowPa
rallels,
Inc.
x86, IA-64,
x86-64
x86, IA-64, x86-64
Linux,
Windows
Linux, Windows
Propri
etary
VMwar
e ESX
Server
VMwar
e
x86, x86-64 x86, x86-64 No host OS
Windows, Linux,
Solaris,
FreeBSD, OSx86(as
FreeBSD), virtual
appliances, Netware,
OS/2, SCO,
BeOS, Haiku, Darwin,
others: runs arbitrary
OS[notes 1]
Propri
etary
VMwar
e ESXi
VMwar
e
x86, x86-64 x86, x86-64 No host OS
Same as VMware ESX
Server
Propri
etary
VMwar
e
Fusion
VMwar
e
x86, x86-64 x86, x86-64 OS X x86
Same as VMware ESX
Server
Propri
etary
VMwar
e
Server
VMwar
e
x86, x86-64 x86, x86-64
Windows,
Linux
Same as VMware ESX
Server
Propri
etary
VMwar VMwar x86, x86-64 x86, x86-64 Windows, Same as VMware ESX Propri

17. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
e
Workst
ation
e Linux Server etary
VMwar
e
Player
VMwar
e
x86-64 x86, x86-64
Windows,
Linux
Same as VMware ESX
Server
Propri
etary,
free of
charge
for
person
al non-
comm
ercial
use[9][10]
Wind
RiverH
ypervis
or
Wind
River
x86, x86-64,
PowerPC,
ARM
Same as host No host OS
Linux, VxWorks,
unmodified guests
(including MS Windows
and RTOSes such ach
OSE, QNX and others),
bare metal virtual board
Propri
etary
Wind
RiverVx
Works
MILS
Platfor
m
Wind
River
PowerPC Same as host No host OS
VxWorks, bare metal
virtual board
Propri
etary
Xen
Xenso
urce,
Now Ci
trix
Syste
ms
x86, x86-64,
ARM, IA-64
(inactive),
PowerPC
(inactive)
Same as host
GNU/Linux,
Unix-like
GNU/Linux, FreeBSD,
MiniOS, NetBSD,
Solaris, Windows
7/XP/Vista/Server 2008
(requires Intel VT-
x (Vanderpool)
or AMD-V(Pacifica)-
capable CPU), Plan 9
GNU
GPLv2
+
XenSer
ver
By Citri
x
Syste
ms
x86, x86-64,
ARM, IA-64
(inactive),
PowerPC
(inactive)
Same as host No host OS
GNU/Linux, FreeBSD,
MiniOS, NetBSD,
Solaris, Windows
7/XP/Vista/Server 2008
(requires Intel VT-
x (Vanderpool)
or AMD-V(Pacifica)-
capable CPU), Plan 9
GNU
GPLv2
+
XtratuM
Univer
sidad
Politec
nica de
Valenci
a
x86, x86;
SPARC v8
LEON2/3
Same as host No host OS
GPOS: Linux, RTOS:
PartiKle, RTEMS
GPL

18. Nam
e
Crea
tor
Host CPU Guest CPU Host OS Guest OS
Lic
ens
e
z/VM IBM z/Architecture
z/Architecture,
z/VM does not run
on predecessor
mainframes
No host OS,
itself (single
or multiple
levels/versio
ns deep,
e.g.
VM/ESA
running in
z/VM 4.4 in
z/VM 5.2 in
z/VM 5.1.)
Linux on
zSeries, z/OS, z/VSE, z
/TPF,
z/VM, VM/CMS, MUSI
C/SP, OpenSolaris for
System z,
predecessors
Propri
etary
z LPAR
s
IBM z/Architecture z/Architecture
Integrated in
firmware
of System
zmainframe
s
Linux on
zSeries, z/OS, z/VSE, z
/TPF,z/VM, MUSIC/SP,
and predecessors
Integr
ated in
firmwa
re
ofSyst
em
zmainf
rames
Name
Creato
r
Host CPU Guest CPU Host OS(s) Guest OS(s)
Licen
se
You scrolled down trough that – right? I was sure. Well there’s nothing more to it actually.
But what is the cloud?
The Cloud
Chris Wodford explains:
“Cloud computing means that instead of all the computer hardware and software you're using sitting on
your desktop, or somewhere inside your company'snetwork, it's provided for you as a service by
another company and accessed over the Internet, usually in a completely seamless way. Exactly where
the hardware and software is located and how it all works doesn't matter to you, the user—it's just
somewhere up in the nebulous "cloud" that the Internet represents.
Cloud computing is a buzzword that means different things to different people. For some, it's just
another way of describing IT (information technology) "outsourcing"; others use it to mean any

19. computing service provided over the Internet or a similar network; and some define it as any bought-in
computer service you use that sits outside your firewall. However we define cloud computing, there's no
doubt it makes most sense when we stop talking about abstract definitions and look at some simple,
real examples—so let's do just that.
Simple examples of cloud computing
Most of us use cloud computing all day long without realizing it. When you sit at your PC and type a
query into Google, the computer on your desk isn't playing much part in finding the answers you need:
it's no more than a messenger. The words you type are swiftly shuttled over the Net to one of Google's
hundreds of thousands of clustered PCs, which dig out your results and send them promptly back to you.
When you do a Google search, the real work in finding your answers might be done by a computer
sitting in California, Dublin, Tokyo, or Beijing; you don't know—and most likely you don't care!
The same applies to Web-based email. Once upon a time, email was something you could only send and
receive using a program running on your PC (sometimes called a mail client). But then Web-based
services such as Hotmail came along and carried email off into the cloud. Now we're all used to the idea
that emails can be stored and processed through a server in some remote part of the world, easily
accessible from a Web browser, wherever we happen to be. Pushing email off into the cloud makes it
supremely convenient for busy people, constantly on the move.
Preparing documents over the Net is a newer example of cloud computing. Simply log on to a web-
based service such as Google Documents and you can create a document, spreadsheet, presentation, or
whatever you like using Web-based software. Instead of typing your words into a program like Microsoft
Word or OpenOffice, running on your computer, you're using similar software running on a PC at one of
Google's world-wide data centers. Like an email drafted on Hotmail, the document you produce is
stored remotely, on a Web server, so you can access it from any Internet-connected computer,
anywhere in the world, any time you like. Do you know where it's stored? No! Do you care where it's
stored? Again, no! Using a Web-based service like this means you're "contracting out" or "outsourcing"
some of your computing needs to a company such as Google: they pay the cost of developing the
software and keeping it up-to-date and they earn back the money to do this through advertising and
other paid-for services.
What makes cloud computing different?
It's managed
Most importantly, the service you use is provided by someone else and managed on your behalf. If
you're using Google Documents, you don't have to worry about buying umpteen licenses for word-
processing software or keeping them up-to-date. Nor do you have to worry about viruses that might
affect your computer or about backing up the files you create. Google does all that for you. One basic
principle of cloud computing is that you no longer need to worry how the service you're buying is
provided: with Web-based services, you simply concentrate on whatever your job is and leave the
problem of providing dependable computing to someone else.

20. It's "on-demand"
Cloud services are available on-demand and often bought on a "pay-as-you go" or subscription basis. So
you typically buy cloud computing the same way you'd buy electricity, telephone services, or Internet
access from a utility company. Sometimes cloud computing is free or paid-for in other ways (Hotmail is
subsidized by advertising, for example). Just like electricity, you can buy as much or as little of a cloud
computing service as you need from one day to the next. That's great if your needs vary unpredictably: it
means you don't have to buy your own gigantic computer system and risk have it sitting there doing
nothing.
It's public or private
Now we all have PCs on our desks, we're used to having complete control over our computer systems—
and complete responsibility for them as well. Cloud computing changes all that. It comes in two basic
flavors, public and private, which are the cloud equivalents of the Internet and Intranets. Web-based
email and free services like the ones Google provides are the most familiar examples of public clouds.
The world's biggest online retailer, Amazon, became the world's largest provider of public cloud
computing in early 2006. When it found it was using only a fraction of its huge, global, computing
power, it started renting out its spare capacity over the Net through a new entity called Amazon Web
Services. Private cloud computing works in much the same way but you access the resources you use
through secure network connections, much like an Intranet. Companies such as Amazon also let you use
their publicly accessible cloud to make your own secure private cloud, known as a Virtual Private Cloud
(VPC), using virtual private network (VPN) connections.
Types of cloud computing
IT people talk about three different kinds of cloud computing, where different services are being
provided for you. Note that there's a certain amount of vagueness about how these things are defined
and some overlap between them.
 Infrastructure as a Service (IaaS) means you're buying access to raw computing hardware over
the Net, such as servers or storage. Since you buy what you need and pay-as-you-go, this is
often referred to as utility computing. Ordinary web hosting is a simple example of IaaS: you pay
a monthly subscription or a per-megabyte/gigabyte fee to have a hosting company serve up files
for your website from their servers.
 Software as a Service (SaaS) means you use a complete application running on someone else's
system. Web-based email and Google Documents are perhaps the best-known examples. Zoho
is another well-known SaaS provider offering a variety of office applications online.
 Platform as a Service (PaaS) means you develop applications using Web-based tools so they run
on systems software and hardware provided by another company. So, for example, you might
develop your own ecommerce website but have the whole thing, including the shopping cart,

21. checkout, and payment mechanism running on a merchant's server. Force.com (from
salesforce.com) and the Google App Engine are examples of PaaS.
Advantages and disadvantages of cloud computing
What's good and bad about cloud computing?
Advantages
The pros of cloud computing are obvious and compelling. If your business is selling books or repairing
shoes, why get involved in the nitty gritty of buying and maintaining a complex computer system? If you
run an insurance office, do you really want your sales agents wasting time running anti-virus software,
upgrading word-processors, or worrying about hard-drive crashes? Do you really want them cluttering
your expensive computers with their personal emails, illegally shared MP3 files, and naughty YouTube
videos—when you could leave that responsibility to someone else? Cloud computing allows you to buy
in only the services you want, when you want them, cutting the upfront capital costs of computers and
peripherals. You avoid equipment going out of date and other familiar IT problems like ensuring system
security and reliability. You can add extra services (or take them away) at a moment's notice as your
business needs change. It's really quick and easy to add new applications or services to your business
without waiting weeks or months for the new computer (and its software) to arrive.
Drawbacks
Instant convenience comes at a price. Instead of purchasing computers and software, cloud computing
means you buy services, so one-off, upfront capital costs become ongoing operating costs instead. That
might work out much more expensive in the long-term.
If you're using software as a service (for example, writing a report using an online word processor or
sending emails through webmail), you need a reliable, high-speed, broadband Internet connection
functioning the whole time you're working. That's something we take for granted in countries such as
the United States, but it's much more of an issue in developing countries or rural areas where
broadband is unavailable.

22. If you're buying in services, you can buy only what people are providing, so you may be restricted to off-
the-peg solutions rather than ones that precisely meet your needs. Not only that, but you're completely
at the mercy of your suppliers if they suddenly decide to stop supporting a product you've come to
depend on. (Google, for example, upset many users when it announced in September 2012 that its
cloud-based Google Docs would drop support for old but de facto standard Microsoft Office file formats
such as .DOC, .XLS, and .PPT, giving a mere one week's notice of the change—although, after public
pressure, it later extended the deadline by three months.) Critics charge that cloud-computing is a
return to the bad-old days of mainframes and proprietary systems, where businesses are locked into
unsuitable, long-term arrangements with big, inflexible companies. Instead of using "generative"
systems (ones that can be added to and extended in exciting ways the developers never envisaged),
you're effectively using "dumb terminals" whose uses are severely limited by the supplier. Good for
convenience and security, perhaps, but what will you lose in flexibility? And is such a restrained
approach good for the future of the Internet as a whole? (To see why it may not be, take a look at
Jonathan Zittrain's eloquent book The Future of the Internet—And How to Stop It.)
Think of cloud computing as renting a fully serviced flat instead of buying a home of your own. Clearly
there are advantages in terms of convenience, but there are huge restrictions on how you can live and
what you can alter. Will it automatically work out better and cheaper for you in the long term?”