1. Week 1 COM221 Operating Systems

2. 2 Chapter 2 Objectives Identify chips, adapter cards, and other components of a motherboard Describe the components of a processor and how they complete a machine cycle Identify characteristics of various personal computer processors on the market today Define a bit and describe how a series of bits represents data Explain how programs transfer in and out of memory Differentiate among the various types of memory Describe the types of expansion slots and adapter cards Explain the differences among a serial port, a parallel port, a USB port, a FireWire port, and other ports Describe how buses contribute to a computer’s processing speed Identify components in mobile computers and mobile devices Understand how to clean a system unit Understand the different innovations in operating systems development; Appreciate the basic role of an operating system; Identify the major operating system software subsystem managers and their functions; Differentiate among the types of machine hardware on which operating systems run and the basic functionality of the three memory allocation schemes presented.

3. 3 What is an Operating System? A computer consists of Software (Programs) and Hardware (CPU, Memory, Motherboard etc). The operating system is a software component of a computer system that manages all the hardware and software. It controls every file, every device, allocation of processing time and memory. It controls who can use the system and how.

4. 4 Operating System Software Every operating system performs four essential functions. Memory management, processor management, Device management and file management. Each function is carried out with the respective manager Memory manager, Processor Manager, Device manager and File manager. Each of the processor must perform the following tasks  Monitor its resources continuously  Apply policies on how each resource is allocated and to whom  Allocate the resources that is handling  Deallocate the resources when needed

5. 5 Kernel Kernel is the core of the operating system. It resides in main memory at all times and performs the most essential tasks such as managing memory, process scheduling etc

6. 6 Data Representation How do computers represent data?  Recognize only two discrete states: on or off  Use a binary system to recognize two states  Use Number system with two unique digits: 0 and 1, called bits (short for binary digits)  Most computers are digital

7. 7 Data Representation What is a byte?  Eight bits grouped together as a unit  Provides enough different combinations of 0s and 1s to represent 256 individual characters  Numbers  Uppercase and lowercase letters  Punctuation marks  Other

8. 8 Data Representation How is a letter converted to binary form and back? Step 3. The system unit converts the scan code for the capital letter T to its ASCII binary code (01010100) and stores it in memory for processing. Step 2. An electronic signal for the capital letter T is sent to the system unit. Step 4. After processing, the binary code for the capital letter T is converted to an image, and displayed on the output device. T Step 1. The user presses the capital letter T (SHIFT+T key) on the keyboard.

9. 9 Memory What is memory?  Electronic components that store instructions, data, and results  Consists of one or more chips on motherboard or other circuit board  Each byte stored in unique location called an address, similar to seats in a concert hall

10. 10 Memory How is memory measured? TermAbbreviationApproximate Size KilobyteKB or K1 thousand bytes MegabyteMB1 million bytes GigabyteGB1 billion bytes TerabyteTB1 trillion bytes  By number of bytes available for storage

11. 11 Memory ROM (Read Only Memory) -Special memory used to store programs(ex. BIOS) that boot the computer and perform diagnostics -Non-volatile -Variations: PROM, EPROM, EEPROM, Flash Memory

12. 12 Storage(Disk) Hard disk -A magnetic disk on which you can store large volumes data. -Internal hard disk & portable hard disk -Several platters with tracks, read/write head and an access arm -100Gbyte – Tbyte -Term : IDE, ATA – disk drive implementation that integrates the controller on the disk drive itself Other disks – Zip, Jaz, tapes, CD, DVD

13. 13 Characteristics of Memory  The term location refers to whether memory is internal and external to the computer.  Internal memory is often equated with main memory.  There are other forms of internal memory.  The processor requires its own local memory, in the form of registers.  The control unit portion of the processor may also require its own internal memory.  Cash is another form of internal memory.  External memory consists of peripheral storage devices, such as disk and tape, that are accessible to the processor via I/O controllers.

14. 14 Characteristics of Memory  Capacity is an obvious characteristic of internal memory, this is typically expressed in terms of bytes (1 byte = 8 bits) or words.  Common word lengths are 8, 16, and 32 bits.  External memory capacity is typically expressed in terms of bytes.

15. 15 Three concepts for internal memory:  Word:  The «natural» unit of organization of memory. The size of the word is typically equal to the number of bits used to represent a number and to the instruction length.  Addressable units:  The addressable unit is the word.  Many systems allow addressing at the byte level.  The relationship between the length in bits A of an address and the number N of addressable units is 2 A =N.  Unit of transfer:  For main memory, this is the number of bits read out of or written into memory at a time. The unit of transfer need not equal a word or an addressable unit.  For external memory, data are often transferred in much larger units than a word, and these are refered to as blocks.

16. 16 The two most important characteristics of memory  From a user’s point of view the two most important characteristics of memory are capacity and performance.  Three performance parametres are used:  Access time (latency):  For random-access memory, this is the time it takes to perform a read or write operation, that is, the time from the instant that an address is presented to the memory to the instant that data have been stored or made available for use.  For non-random-access-memory, access time is the time it takes to position the read-write mechanism at the desired location.

17. 17 The two most important characteristics of memory  From a user’s point of view the two most important characteristics of memory are capacity and performance.  Three performance parametres are used:  Memory cycle time:  This concept is primarily applied to random-access memory and consists of the access time plus any additional time required before a second access can commence.

18. 18 Memory What is random access memory (RAM)? The more RAM a computer has, the faster it responds Also called main memory or primary storage Most RAM is volatile, it is lost when computer’s power is turned off Memory chips that can be read from and written to by processor

19. 19 Memory How do program instructions transfer in and out of RAM? Step 1. When you start the computer, certain operating system files are loaded into RAM from the hard disk. The operating system displays the user interface on the screen. Operating system instructions Web browser instructions Paint program instructions Operating system interface Web browser window Paint program window Web browser program instructions are removed from RAM Web browser window is no longer displayed on desktop Step 2. When you start a Web browser, the program’s instructions are loaded into RAM from the hard disk. The Web browser window is displayed on the screen. Step 3. When you start a paint program, the program’s instructions are loaded into RAM from the hard disk. The paint program, along with the Web Browser and certain operating system instructions are in RAM. The paint program window is displayed on the screen. Step 4. When you quit a program, such as the Web browser, its program instructions are removed from RAM. The Web browser is no longer displayed on the screen. RAM

20. 20 Must be re-energized constantly Do not have to be re-energized as often as DRAM Most common type Faster and more reliable than DRAM chips Memory What are two basic types of RAM chips? Static RAM (SRAM) Dynamic RAM (DRAM) Newer Type: Magnetoresistive RAM (MRAM)

21. 21 Memory. Organization  The basic element of a semiconductor memory is the memory cell. Although a variety of electronic technologies are used, all semiconductor memory cells share certain properties:  They exhibit two stable (or semistable) states, which can be used to represent binary 1 and 0.  They are capable of being written into (at least once), to set the state.  They are capable of being read to sense the state.

22. 22 DRAM and SRAM  One distinguishing characteristic of RAM is that it is possible both to read data from the memory and to write new data into the memory easily and rapidly. Both the reading and writing are accomplished through the use of electrical signals.  The other distinguishing characteristic of RAM is that it is volatile.  A RAM must be provided with a constant power supply.  If the power is interrupted, then the data are lost.  Thus, RAM can be used only as temporary storage.  The two traditional forms of RAM used in computer are DRAM and SRAM.

23. 23 Dynamic RAM  RAM technology is divided into two technologies: dynamic and static.  A dynamic RAM (DRAM) is made with cells that store data as charge on capacitors (or condenser is a passive electronic component).  The presence or absence of charge on a capacitor is interpreted as a binary 1 or 0, because capacitors have a natural tendency to discharge, dynamic RAMs require periodic charge refreshing to maintain data storage. The term dynamic refers to this tendency of the stored charge to leak away, even with power continuously applied.

24. 24 Semiconductor Memory Types Memory TypeCategoryErasureWrite Mechanism Volatility UsagePrice Random-access memory (RAM) Electrically, byte level Electrically Read-only memory (ROM) Not possibleMasks Programmable ROM (PROM) Electrically Erasable PROM (EPROM) UV light, chip level Electrically Electrically Erasable PROM (EEPROM) Electrically, byte level Electrically Flash memoryElectrically, block level Electrically

25. 25 Static RAM  In contrast, a static RAM (SRAM) is a digital device, using the same logic elements used in the processor.  A static RAM will hold its data as long as power is supplied to it.

26. 26 SRAM versus DRAM  Both static and dynamic RAMs are volatile: that is, power must be continuously supplied to the memory to preserve the bit values.  A dynamic memory cell is simpler and smaller than a static memory cell. Thus, a DRAM is more dense (smaller cells = more cells per unit area) and less expensive than a corresponding SRAM. On the other hand, a DRAM requires the supporting refresh circuitry (circuits). For larger memories, the fixed cost of the refresh circuitry is more than compensated for by the smaller variable cost of DRAM cells. Thus, DRAMs tend to be favored for large memory requirements.  A final point is that SRAMs are generally somewhat faster than DRAMs. Because of these relative characteristics, SRAM is used for cache memory (both on and off chip), and DRAM is used for main memory.

27. 27 Memory Where does memory reside?  Resides on small circuit board called memory module  Memory slots on motherboard hold memory modules

28. 28 Memory How much RAM does an application require?  Depends on the types of software you plan to use  For optimal performance, you need more than minimum specifications

29. 29 Memory How much RAM do you need?  Depends on type of applications you intend to run on your computer RAM Use 512 MB to 1 GB1 GB to 2 GB 2 GB and up Home and business users managing personal finances Using standard application software such as word processing Using educational or entertainment CD-ROMs Communicating with others on the Web Users requiring more advanced multimedia capabilities Running number-intensive accounting, financial, or spreadsheet programs Using voice recognition Working with videos, music, and digital imaging Creating Web sites Participating in video conferences Playing Internet games Power users creating professional Web sites Running sophisticated CAD, 3D design, or other graphics-intensive software

30. 30 Memory What is cache?  L1 cache built into processor  L2 cache slower but has larger capacity  L2 advanced transfer cache is faster, built directly on processor chip  L3 cache is separate from processor chip on motherboard (L3 is only on computers that use L2 advanced transfer cache)  Helps speed computer processes by storing frequently used instructions and data  Also called memory cache

31. 31 Cache memory principles  Cache memory is intended to give memory speed approaching that of the fastest memories available, and at the same time provide a large memory size at the price of less expensive types of semiconductor memories.  The concept is illustrated in the figure below. There is a relatively large and slow main memory together with a smaller, faster cache memory.  The cache contains a copy of portions of main memory.

32. 32 Cache memory principles  When the processor attempts to read a word of memory, a check is made to determine if the word is in the cache. If so, the word is delivered to the process. If not, a block of main memory, consisting of some fixed number of words, is read into the cache and then the word is delivered to the processor. CPUCache Main memory Word transfer Block transfer

33. 33 Computer Components  Virtually all contemporary computer designs are based on concepts developed by John von Neumann at the Institute for Advanced Studies, Princeton.  Such a design is referred to as the von Neumann architecture and is based on three key concepts: -Data and instructions are stored in a single read-write memory. -The contents of this memory are addressable by location, without regard to the type of data contained there. -Execution occurs in a sequential fashion (unless explicitly modified) from one instruction to the next.

34. 34 The Components of the System Unit: Differentiate among various styles of system units; Computer Function  The basic function performed by a computer is execution of a program, which consists of a set of instructions stored in memory.  The processor does the actual work by executing instructions specified in the program.  This section provides an overview of the key elements of program execution.  Instruction processing consists of two steps:  The processor reads (fetches) instructions from memory one at a time and executes each instruction.

35. 35 Computer Function  Program execution consists of repeating the process of instruction fetch and instruction execution. -The instruction execution may involve several operations and depends on the nature of the instruction.

36. 36 The von Neumann Machine  The computer consists of the following: -A main memory, which stores both data and instructions -An arithmetic and logic unit (ALU) capable of operating on binary data -A control unit, which interprets the instructions in memory and causes them to be executed -Input and output (I/O) equipment operated by the control unit

37. 37 The von Neumann Machine  With rare exceptions, all of today’s computers have the same general structure and function and are thus referred to as von Neumann machines.  Description of the operation of the computer -The memory of the computer consists of 1000 storage locations, called words, of 40 binary digits (bits) each. Both data and instructions are stored there. Numbers must be represented in binary form, and each instruction also has to be a binary code.

38. 38 The von Neumann Machine 0139 Sign bit Figure 1.3 Memory Formats. 0 39 28208 Right instruction Left instruction AddressOpcodeAddressOpcode (a) Number word (b) Instruction word

39. 39 The von Neumann Machine  The memory of the computer consists of 1000 storage locations, called words, of 40 binary digits (bits) each. Both data and instructions are stored there. Numbers must be represented in binary form, and each instruction also has to be a binary code.  Figure 1.3 illustrates these formats. Each number is represented by a sign bit and a 39- bit value. A word may also contain two 20 bit instructions, with each instruction consisting of an 8-bit operation code (opcode specifying the operation to be performed and a 12-bit address designating one of the words in memory (numbered from 0 to 999). -Physical memory that is internal to the computer -Random Access Memory, Read & Write -An array of boxes, each of which can hold a single byte of information -CPU can manipulate only data that is in main memory -Amount of main memory determines how many programs can be executed at a time. -Type: DRAM(Dynamic Ram) – need to be refreshed, SRAM(Static Ram)- no need to refresh, faster, expensive -Volatile – lose its data when power is out -Swapping : A technique that maintains portion of data in the memory when the memory is not large enough -Virtual memory

40. The System Unit What is the system unit?  Case that contains electronic components of the computer used to process data  Sometimes called the chassis

41. The System Unit What are common components inside the system unit?  Memory  Adapter cards  Sound card  Video card  Drive bays  Power supply  Processor

42. The System Unit What is the motherboard?  Main circuit board of the system unit  Contains expansion slots, processor chips, and memory slots  Also called system board

43. The System Unit What is a chip?  Small piece of semi-conducting material on which integrated circuits are etched  Integrated circuits contain many microscopic pathways capable of carrying electrical current  Chips are packaged so they can be attached to a circuit board

44. 44 Memory Management Main-Memory is a large array of words or bytes. Each word or byte has its own address. Main memory is a repository of quickly accessible data shared by the CPU and I/O devices. The central processor reads instructions from main memory during the instruction-fetch cycle, and both reads and writes data from main memory during the data- fetch cycle. The I/O operations implemented via DMA also read and write data in main memory. The main memory is generally the only large storage device that the CPU is able to address and access directly.

45. 45 Memory Management To improve both the utilization of CPU and the speed of the computer's response to its users, we must keep several programs in memory. There are many different memory-management schemes. The major activities of an operating system in regard to memory-management are:  Keep track of which part of memory are currently being used and by whom  Decide which processes are loaded into memory when memory space becomes available.  Allocate and deallocate memory space as needed.

46. Processor Control Unit Arithmetic Logic Unit (ALU) Processor What is the central processing unit (CPU)? Input Devices Storage Devices Output Devices  Interprets and carries out basic instructions that operate a computer Memory DataInformation Instructions Data Information Control Unit  Control unit directs and coordinates operations in computer  Arithmetic logic unit (ALU) performs arithmetic, comparison, and logical operations  Also called the processor

47. Processor What is pipelining?  Processor begins fetching second instruction before completing machine cycle for first instruction  Results in faster processing

48. Stores location from where instruction was fetched Processor Stores instruction while it is being decoded What is a register? Stores data while ALU computes it Stores results of calculation  Temporary high-speed storage area that holds data and instructions

49. Processor What are dual-core and multi-core processors?  A dual-core processor is a single chip that contains two separate processors  A multi-core processor is a chip with two or more separate processors  Each processor on a dual-core/multi-core chip generally runs at a slower clock speed, but increase overall performance

50. Processor What are the guidelines for selecting a processor?

51. Processor What are heat sinks, heat pipes, and liquid cooling?  Heat sink—component with fins that cools processor  Heat pipe e —smaller device for notebook computers  Liquid cooling—uses a continuous flow of fluids to transfer heat away

52. Processor What is parallel processing? Control Processor Processor 1 Memory Processor 2 Memory Processor 3 Memory Processor 4 Memory Results combined  Using multiple processors simultaneously to execute a program faster  Requires special software to divide problem and bring results together

53. Structure and Function  A computer is a complex system; contemporary computers contain millions of elementary electronic components.  A hierarchical system is a set of interrelated subsystems.  The system consists of a set of components and their interrelationships. The behavior at each level depends only on a simplified, abstracted characterization of the system at the next lower level. At each level, the designer is concerned with structure and function: 1.Function: The operation of each individual component as part of the structure. 2.Structure: The way in which the components are interrelated.

54. 1.1 Function  Both the structure and functioning of a computer are, in essence, simple. Figure 1.1 depicts the basic function that a computer can perform. In general terms, there are only four:  Data Processing  Data storage  Data movement  Control Data Movement apparatus Data Processing facility Data Storage facility Control mechanism Figure 1.1 A Functional View of the Computer

55. 1.2 Function  The computer must be able to process data. The data may take a wide variety of forms, and the range of processing requirements is broad.  It is also essential that a computer stores data. -The computer performs a short-term data storage -The computer performs a long-term data storage -Files of data are stored on the computer for subsequent retrieval and update.

56. 1.3 Function  The computer must be able to move data between itself and the outside world. -The computer’s operating environment consists of devices that serve as either sources or destination of data. -When data are received from or delivered to a device that is directly connected to the computer, the process is known as input-output (I/O), and the device is referred to as a peripheral. -When data are moved over longer distances, to or from a remote device, the process is known as data communications.

57. 1.4 Function  There must be control of these three functions. -Within the computer, a control unit manages the computer’s resources and orchestrates the performance of its functional parts in response to those instructions.

58. 2.1 Structure  There are four main structural components - Central processing unit (CPU): Controls the operation of the computer and performs its data processing functions; often simply referred to as processor -Main memory: Stores data -I/O: Moves data between the computer and its external environment -System interconnection: Some mechanism that provides for communication among CPU, main memory, and I/O -Traditionally, there has been just a single CPU. In recent years, there has been increasing use of multiple processors in a single computer.

59. 2.2 Structure  The most interesting and complex component is the CPU; its major structural components are as follows: - Control Unit: Controls the operation of the CPU and the computer -Arithmetic and logic unit (ALU): Performs the computer’s data processing functions -Registers: Provides storage internal to the CPU -CPU interconnection: Some mechanism that provides for communication among the control unit, ALU, and registers

60. 2.3 Structure System interconnection Central processing unit Input/ output Main memory COMPUTER Figure 1.2 The Computer: Top-Level Structure

61. I/O Interfacing (Peripheral devices)  I/O  Any program, operation or device that transfers data to or from a computer and to or from a peripheral device  Peripheral Device  A computer device, such as a CD-ROM drive or printer, that is not part of the essential computer, i.e., the memory and microprocessor.  External & Internal  Bus  A collection of wires through which data is transmitted from one part of a computer to another  Internal Bus(System Bus, Host bus) between internal computer component to CPU & main memory  Expansion Bus for expansion board(card) to CPU & main memory  Performance : Bus size (with) (bit), Bus clock speed (MHz)  Type : ISA(old), PCI, AGP, SCSI  (Bus) Controller  A device( a chip) that controls the transfer of data from a computer to a peripheral device and vice versa

62. I/O Interfacing (Peripheral devices)

63. 63 User Command interface  Every operating system provides an interface that accepts commands from the operator. This interface can be in the form of a command-line interface or in the form of a Graphical User Interface (GUI). Command line interfaces were very common on early systems and UNIX systems. GUI (Windows) interfaces are widespread used on Apple and Windows operating systems.

64. 64 Types of operating systems  Operating systems can be distinguished into five categories based on their response time and how the data is entered in to the system.  Batch Systems :  In a batch system programs to be run were collected in a designated area, read onto a magnetic tape using a small, relatively inexpensive computer. After collecting jobs in this manner for a prescribed period of time, the tape was rewound and mounted on a tape drive connected to the main computer where the programs were run one after the other. The output from each program was collected onto a second tape. When the entire batch was processed, the operator removed both tapes and passed the one with the outputs on to be printed by the same small computer connected to a printer. The operator then mounted another tape with another batch of programs to be run.

65. 65 Types of operating systems  Interactive Systems  Interactive systems are a variation of multiprogramming systems because they allow several users to be on-line at the same time. The computer can provide fast interactive service to several users, and programmers can debug their programs in a shorter period of time than was possible with batch systems. This is because not all users are issuing commands to the computer at the same time. For example, of 300 users logged on there may be only 20 percent actively working at any given time allowing the CPU to handle their requests in a timely manner. In addition, some of the commands may take a small amount of CPU time to complete, for example to compile a student program, while others may take a longer time to finish, thus balancing the workload.

66. 66 Types of operating systems  Real Time Systems  Real-time systems are used in time critical environments such as vehicle control or patient monitoring where failures in the system could lead to loss of life or major destruction of property. They are usually considered dedicated systems which spend most of the time on a single job. Work such as laboratory experiment monitoring, or environment control within buildings requires continuous processing, with little opportunity to use the computer for unrelated purposes.

67. 67 Types of operating systems  Hybrid Systems  Hybrid Systems are a combination of batch and Interactive systems. Batch jobs are running the background when the interactive activity is low. They are utilizing system resources efficiently.

68. 68 Types of operating systems  Embedded Systems  Embedded systems are computers systems that are placed inside other devices. They have all the main components of a computer system (CPU, memory) but are performing specific functions to enhance the functionality of the device. They can only run specific programs and they make very efficient use of their limited resources.

69. 69 Desktop and server Operating systems  Operating systems can be classified based on the users’ accessibility into Desktop operating systems and Server operating Systems.

70. 70 Desktop Operating systems  Desktop Operating systems are used on single user systems. They are used on personal computers that perform general tasks such as writing documents and internet browsing. Examples of Desktop operating systems are Windows XP, Windows 7, Linux Ubuntu desktop edition.

71. 71 Server Operating systems  Server operating systems are used on multiuser systems. Many users can access the system concurrently via the network. They perform functions such as File sharing, mail servers, web servers, application servers. Examples of server operating systems are Windows Server 2008, UNIX and IBM Mainframes.

72. 72 Device management The Device Manager is in charge of monitoring the device connected to the Computer systems such as disk drives, printers, ports etc. It allocates and deallocates these resources to the running process based on scheduling policy.

73. 73 History of Operating Systems  Historically operating systems have been tightly related to the computer architecture, it is good idea to study the history of operating systems from the architecture of the computers on which they run. Operating systems have evolved through a number of distinct phases or generations which corresponds roughly to the decades.

74. 74 History of Operating Systems The 1940's - First Generations  The first generation of Computers were bulky and expensive. They were used only by research institutions and universities. Each one was unique. They had no operating systems. Machines of the time were so primitive that programs were often entered one bit at time on rows of mechanical switches (plug boards). Programming languages were unknown (not even assembly languages). The machines were operated by the programmers and it was mainly manual work. They were poorly utilized. The programs were only understandable form the person that develops them.

75. 75 History of Operating Systems The 1950's - Second Generation  Second generation computers were started to be used by business. They were still very expensive and only big business could afford them. The General Motors Research Laboratories implemented the first operating systems in early 1950's for their IBM 701. The system of the 50's generally ran one job at a time. These were called single-stream batch processing systems because programs and data were submitted in groups or batches.

76. 76 History of Operating Systems The 1960's - Third Generation  The systems of the 1960's were also batch processing systems, but they were able to take better advantage of the computer's resources by running several jobs at once. So operating systems designers developed the concept of multiprogramming in which several jobs are in main memory at once; a processor is switched from job to job as needed to keep several jobs advancing while keeping the peripheral devices in use.

77. 77 History of Operating Systems The 1970’s  CPUs were becoming faster but the I/O devices were still slow. Multiprogramming was limited by the memory capacity of the system. Memory was very expensive. The concept of virtual memory was developed where not the whole program needed to be loaded in the memory. Part of it could be kept in secondary storage and loaded only when needed. Organization of data into databases was becoming popular. Database tools were becoming available.

78. 78 History of Operating Systems The 1980’s  Computers became much more cost effective. Many functions were carried out by separated hardware components with build-in system software. Programmers did not have to deal directly with the hardware and their job was simpler. Multiprocessing (more than one processor) was introduced where a single job is served by many processors. It was the era of the evolution of personal computers that were able to connect with each. Network operating systems were introduced that allow networked computers to share resources.

79. 79 History of Operating Systems The 1990’s  Internet was evolved connecting computers worldwide. Computer’s networking capability was enhanced. Web accessibility and email became standard on almost all operating systems. New devices appeared that can connect to computers to provide multimedia capabilities such as microphones, speakers, DVD drives, CD drives, projectors etc.

80. 80 History of Operating Systems The 2000’s Processing speed of computers was significantly improved with the introduction of multicore processors. A single CPU chip can hold multiple processors cores that act as separate processors and therefore multiplying their processing capacity. Virtualization started to become popular. Virtualization allows us to run multiple operating systems on a single server and share resources.