Operating System Fundamentals PDF

1️⃣ Operating System Fundamentals An Introduction to Operating Systems Operating System Categories Single-Tasking Versus Multitasking Operating Systems Single-User Versus Multiuser Operating Systems...

1️⃣ Operating System Fundamentals An Introduction to Operating Systems Operating System Categories Single-Tasking Versus Multitasking Operating Systems Single-User Versus Multiuser Operating Systems General-Purpose Versus Real-Time Operating Systems Operating System Roles. Client Operating Systems Server Operating Systems Standalone Operating Systems A Short History of Operating Systems An Introduction to Operating Systems A computer’s functions and features can be broken down into the three basic tasks all computers perform: input, processing, and output. Information is input to a computer from an input device such as a keyboard or sensor, or from a storage device such as a disk drive; the central processing unit (CPU) processes the information, and then output is usually created. The following example illustrates the process: Input - A user running a word-processing program types the letter A on the keyboard, which results in sending a code to the computer representing the letter A. Processing - The computer’s CPU determines what letter was typed by looking up the keyboard code in a table that resides within the computer’s memory and is part of the operating system Output - The CPU sends instructions to the graphics cards to display the letter A, which is then sent to the computer monitor. The three functions described above involve some type of computer hardware, but the hardware is controlled and coordinated by the operating system. Without an operating system, every application you use would have to Operating System Fundamentals 1  know the details of how to work with each of the hardware devices. Without the operating system to coordinate things, only one application could run at a time. For example, you couldn’t open a Web browser while working on a Word document. The operating system can be seen as the go-between for the applications you run and the computer hardware. In a nutshell, an operating system (OS) is a computer program that provides the following features: User interface - The user interface provides a method for users to interact with the computer, usually with a keyboard and mouse or touch screen. A user clicks, touches, or types; the computer processes the input and provides some type of output. Storage management - A key function of business computers is the storage of information. The file system is the method by which an OS stores and organizes files and manages access to files on a storage device, such as a disk drive, SD card, or USB flash drive. Process and service management - A process is a program that’s loaded into memory and run by the CPU. It can be an application a user interacts with, such as a Web browser, or a program with no user interface that communicates with and provides services to other processes. A process without a user interface that runs in the background is usually called a service in Windows and a “daemon” in Linux. Most operating systems have built-in services to handle network communication, control access to various input/output devices, manage the file system, and so forth. The operating system controls the loading, execution, and termination of both built-in and user-installed processes. Memory and I/O management - When a user performs an action that starts an application, the OS must determine if sufficient memory exists to load the application and where in memory it should be loaded. When an application terminates, the OS must mark the memory used by the application as free so other applications may use it. In addition, the OS ensures that I/O devices such as USB ports and video cards are accessed by only one process at a time. Security and resource protection - Operating systems used on business systems provide methods for securing access to resources. This function includes protection from accidental unauthorized access, such as when a poorly written program attempts to access memory outside of its allocated Operating System Fundamentals 2  space, and from purposeful unauthorized access, such as from malware or an outside attacker. The OS also provides access controls that can be configured to limit which users can access particular files or make system configuration changes. The kernel - The kernel is the heart of the OS and runs with the highest priority. It performs many of the tasks mentioned in this list. The kernel schedules processes to run, making sure high-priority processes are taken care of first; performs memory and I/O management; and provides a number of security and resource protection functions. Operating System Categories To better understand how operating systems work, it is helpful to understand some of the more common categories of operating systems and the terminology used to describe them. We’ll discuss three broad categories: single-tasking versus multitasking, single-user versus multiuser, and general- purpose versus real-time. Single-Tasking Versus Multitasking Operating Systems As the name suggests, a single-tasking operating system can execute only a single process at a time. This means that if you are browsing the Internet with a Web browser, you can’t be listening to Spotify at the same time on the computer. I know, it’s hard to imagine! A multitasking operating system quickly switches between all the processes that are loaded into memory and scheduled to run, so Spotify can play music while you’re typing a document and the Chrome browser is downloading a file. While most people haven’t experienced a single-tasking OS recently on a desktop or laptop computer, it wasn’t too long ago that a single-tasking system was in widespread use: Apple’s iOS 3 (and earlier versions) was a single- tasking OS for the iPhone and iPad. It wasn’t until June 2010 that iOS 4 brought multitasking to the iPhone and November 2010 that iOS 4.2 allowed multitasking on the iPad. Prior to that, only the app that was visible on the iPhone or iPad screen was actually running. So, if you were using the messaging app, you couldn’t listen to iTunes, for example. Keep in mind that you could have multiple apps loaded into memory at the same time, but only the foreground app (the one visible on the screen) received CPU time. The hardware these early versions of iOS ran on was capable of multitasking, but Operating System Fundamentals 3  Apple was concerned about reliability and managing access to the hardware by third-party apps. Other single-tasking OSs include CP/M, PC-DOS, and MS-DOS, versions of Windows prior to Windows 3, and Palm OS. CP/M, PC-DOS, and MS-DOS are command-line OSs and were the original OSs to run on the IBM PC in the early 1980s. MS-DOS, owned by Microsoft, was the precursor to Windows, which got multitasking capabilities with version 3.0. Palm OS was used in a class of devices called personal digital assistants (PDAs). PDAs were handheld devices that ran email programs, calendars, note-taking apps, Web browsers, and other productivity applications but didn’t have integrated phones. PDAs were an impetus for the development of the smartphone. Another place where you often find single-tasking OSs is in embedded systems. An embedded system is a computing device designed for a specific task, such as controlling a dishwasher or handling the braking system in an automobile. They often use inexpensive microcontrollers that run at speeds as low as 1 MHz, don’t have multitasking capabilities, might have as little as 8 KB of memory, and run a simple OS that does little more than load a program and start it. That isn’t to say that all embedded systems are single-tasking, but many are. Modern business computers and mobile devices use a multitasking operating system. These devices have multiple CPU cores, multiple gigabytes of RAM, and can execute billions of instructions per second. They are built for multitasking, so running a single-tasking OS on them would be a complete waste of computing resources. There are two general types of multitasking. The first method is known as cooperative multitasking. In this method, the operating system gives CPU control to a process and waits for it to terminate or enter a waiting state, thereby giving up control of the CPU. The OS then gives CPU control to the next process waiting for CPU time. The problem with this method of multitasking occurs when a process doesn’t relinquish control of the CPU in a timely manner, either due to poor software design or an error that keeps the process in an infinite loop. In the former case, other tasks are unable to run until the current process terminates. In the latter case, the system will freeze and become unresponsive with no recourse but to reboot the computer. This type of behavior was seen frequently with early versions of Windows because they used cooperative multitasking until Windows 95. Operating System Fundamentals 4  Figure 1-1 shows the basic concept of cooperative multitasking. In the figure, there is a process ready queue of the processes waiting for CPU time. The OS gives CPU control to Process 1. When Process 1 relinquishes control of the CPU, the OS gives CPU control to Process 2, and Process 1 moves to the bottom of the process ready queue (or is removed from memory if it terminates). Figure 1-1 Cooperative multitasking Clearly, cooperative multitasking has drawbacks because the performance of the system as a whole is dependent on all the processes playing by the rules and, as the name suggests, cooperating. A better multitasking method is preemptive multitasking, as illustrated in Figure 1-2. In the figure, the running process can be replaced with another process at any time based on a system interrupt, a higher-priority task requiring the CPU, or the time-slice timer expiring. Operating System Fundamentals 5  Figure 1-2 Preemptive multitasking Operating systems used on server, desktop, and laptop computers developed since the early 2000s use preemptive multitasking operating systems. In preemptive multitasking, the operating system is in strict control of which processes get CPU time. It gives each process a slice of time with the CPU, alternating between processes, including those that belong to the OS. Because the operating system is in charge, it has a lot of control over how much of the computer’s resources are allocated to each program. As a result, the computer must use more of its processor power and memory to support the operating system, but reliability and a responsive computer are the result. Playing music while working in a document and a Web browser on a preemptive multitasking system is not a problem—all processes get enough CPU time to do their jobs— and the user is often unaware that the system has been rapidly switching between tasks. Single-User Versus Multiuser Operating Systems A single-user operating system allows only one user at a time to interact with the OS user interface, start processes, make system configuration changes, and interact directly with the file system. Single-user systems may be single- tasking systems as well, but they don’t have to be. However, all single-tasking systems, such as those mentioned in the previous section, are also single-user systems. Windows 10 and earlier Windows client versions are arguably single- Operating System Fundamentals 6  user systems. A user signs in to the system using a keyboard and mouse and has full purview over system resources. While that user is signed in, no other user may sign in and access the Windows user interface. A protocol called Remote Desktop Protocol (RDP) allows a user to remotely sign in to a Windows 10 system, but only if no user is signed in at the local console. Note that Microsoft has recently introduced a multiuser version of Windows 10, but only as part of a Microsoft Azure feature called Windows Virtual Desktop. While Windows 10 may eventually offer true multiuser support, previous versions of Windows such as Windows 8 and Windows 7 have been single- user systems. Mobile operating systems such as Apple iOS and Android are also single-user systems. Don’t confuse network file sharing with a multiuser system. While network users can access shared files and printers on many single-user systems, they don’t interact directly with the operating system or have the ability to load applications that use the computer’s CPU and memory resources. A true multiuser operating system allows multiple users to sign in to it, start and stop processes (that is, run user applications), interact with the user interface, and access the local file system. Linux/UNIX operating systems have always supported multiple users, and Windows Server versions also allow multiple users through RDP, where one user can be signed in to the local console and other users can be signed in remotely. The remote users have the same access to the Windows user interface, file system, CPU, and memory as the locally signed-in user. A multiuser operating system is, by definition, also a multitasking operating system. General-Purpose Versus Real-Time Operating Systems Most of the operating systems mentioned so far are considered general- purpose operating systems. A general-purpose operating system is designed to provide a convenient user interface and run applications in a home or business environment with reasonable performance. These operating systems usually require a responsive user interface because users expect a file or application to load quickly when they double-click it. Users are not typically concerned with background processes unless they affect the application that is currently running. In short, general-purpose operating systems are designed to run business, productivity, or entertainment applications. A user probably doesn’t care if it takes.5 seconds to calculate a spreadsheet or.7 seconds, as long as it does so correctly and in a reasonable amount of time. Operating System Fundamentals 7  A real-time operating system (RTOS), on the other hand, is designed to process inputs and produce outputs not just in a reasonable amount of time, but in a very specific and repeatable amount of time. Real-time systems perform tasks like controlling assembly line robotic systems, controlling Federal Express sorting facilities, managing the electrical grid, running amusement park rides, and controlling self-driving automobiles. In such systems, the difference between completing a task in.5 seconds or.7 seconds could mean a restart of the assembly line at least or the loss of life at worst. Not only must real-time systems respond quickly to changing conditions, they must be predictable. Components of real-time systems such as the communication network and storage system are called deterministic because it is possible to determine the worst-case response times under a given set of conditions. Examples of RTOSs include VxWorks from Window River Systems; QNX, which is a real-time UNIX- like OS currently owned by BlackBerry; LynxOS, another UNIX-like system owned by Lynx Software Technologies; and Windows 10 IoT, the Internet of Things version of Windows that succeeds Windows CE. Many other proprietary RTOSs are used in particular industry niches. RTOSs are not designed to run business applications on traditional computer hardware. Most of the software that runs on them is custom-developed for embedded system hardware with a custom user interface or no user interface at all. While they may not be as visible as general-purpose OSs, they have become more prevalent in people’s everyday lives, especially because they play an important role in the Internet of Things (IoT). Operating System Roles. Operating systems can be defined by the role they play from the perspective of the user and the system’s interaction or lack thereof with other systems. In some cases, a single operating system can be deployed in multiple roles depending on the application it will serve. You can classify most operating systems as one of the following: Client Server Standalone Client Operating Systems Operating System Fundamentals 8  The primary purpose of a client operating system is to run applications requested by a user and request data from network servers as necessary. Many OSs classified as client operating systems, such as Windows 10 and macOS, and client distributions of Linux, such as Ubuntu Desktop, can perform some server functions, but their primary purpose is to be used as a client. Client OSs are usually installed on desktop or laptop computers and mobile devices and use a graphical user interface (GUI). Client OSs usually include client versions of many network applications. For example, Windows 10 comes with Client for Microsoft Networks for accessing shared files and printers. Linux clients come with the Linux equivalent of Client for Microsoft Networks, called SAMBA, as well as the Linux native file sharing protocol, Network File System (NFS). Client OSs also come preinstalled with the client half of Dynamic Host Configuration Protocol (DHCP) and the Domain Name System (DNS) protocol. In addition, most client OSs are performance-tuned for running foreground applications (user applications) instead of background services. Figure 1-3 shows the Performance Options dialog box in Windows 10. In contrast, Windows Server has Background services selected because most of the work done by servers is performed by services running in the background. Server Operating Systems The primary purpose of a server operating system is to share network resources such as storage and printers and provide network services to clients. Windows Server, macOS Server, UNIX, and many Linux distributions fall in this Operating System Fundamentals 9  category. A server OS is tuned to share files efficiently and perform network operations in response to client requests. It usually comes with server services such as a DHCP server, a DNS server, a file server protocol, a Web server, and perhaps a directory service such as Microsoft’s Active Directory. Server OSs may also be used as virtualization hosts on which several virtual servers can run. For optimal resource usage and performance, many server OSs can be configured to operate without a GUI, so administrators must be familiar with the OS’s command-line interface. For example, the default installation of Windows Server is Windows Server Core, which has no GUI (see Figure 1-4), and most Linux distributions intended as servers are installed with only the shell interface (see Figure 1-5). Figure 1-4 The Windows Server Core initial logon screen Server OSs often have built-in functions for fault tolerance, load sharing, and scalability. Fault tolerance is the ability of a system to recover from a hardware or software failure. For example, a server OS typically supports clustering, which is the ability of two or more servers to act as one, for fault tolerance, load sharing, or both. A server cluster designed for fault tolerance is often called a failover cluster, whereby two or more servers share identical configurations and have shared access to data. If one server fails, another takes over its tasks. A load-sharing cluster, or load-balancing cluster, has two or more servers that alternate in taking client requests, which provides faster Operating System Fundamentals 10  response time to clients. Many servers also support hot swapping of components such as hard disks, memory, and even processors so that if a component fails, a new component Figure 1-5 A Linux shell interface can be swapped in without shutting the system down. For scalability, some servers support hot adding of components so that more storage, RAM, or processors can be added while the system is running. The type of hardware that server OSs are typically installed on also differs from that of client OSs. A server OS is usually installed on a more powerful computer that may have several high-speed network interfaces and terabytes of storage. In addition, fault tolerance is not just a function of the server OS; the hardware must also support fault-tolerant features such as hot swapping and failover clustering—features that client computers lack. The server hardware can also take different forms, including traditional tower computers, rack-mounted servers, and blade servers. Server OSs and some server hardware features are discussed in more detail in Module 10. Standalone Operating Systems A standalone operating system, as the name suggests, is not designed to interact with other OSs or access network resources. You may be hard-pressed to find a standalone OS today, as almost every computing device has a network interface and can, at the very least, connect to the Internet. You’re most likely to find a standalone OS running in an embedded system. If the system has no need to communicate with a network, it can be designed with a very basic OS that has no network interface or an OS with disabled network functions to save Operating System Fundamentals 11  memory and maximize performance. The OSs that run older or isolated traffic signal systems are likely to be standalone, as are the OSs that run automobile electronic systems and industrial machinery. This is changing as computer- controlled devices are being built with IoT in mind, so operational and performance data from these devices can be collected and analyzed to make processes more efficient. Aside from embedded systems, you have to travel back in time to the MS-DOS era and early Windows and Macintosh days to find a general-purpose OS that was standalone. These early OSs didn’t come with networking software, but with a little patience and know-how, they could be “upgraded” to client OS status with third-party software and a network card, usually to connect to a Novell Netware or UNIX server. Now that you have a good idea of OS categories and roles, it’s time to take a closer look at some of the components of modern multitasking operating systems that you’ll find in most general-purpose, real-time, single-user, and multiuser OSs. A Short History of Operating Systems The history of operating systems is a complex and evolving subject, with early computers primarily serving as automated calculators for mathematical and statistical tasks. These machines were large, occupying entire rooms, and were used by scientists who programmed them for specific tasks. Early computers were single-tasking, single-user systems, and the operating systems were basic, primarily managing input through punch cards or tape and output via Teletype machines. The development of operating systems began as a tool to simplify programming for non-computer scientists, leading to increased efficiency and accessibility. By the late 1960s and early 1970s, computers became more capable, contributing to significant advancements in space travel, missile systems, and finance. The evolution of input/output devices, increased memory capacity, and faster processors required more complex operating systems, but the focus remained on keeping them small and efficient. During this period, the introduction of the display terminal (cathode ray tube or CRT), magnetic tape drives, and the concept of sharing computer resources among multiple programs laid the groundwork for modern multitasking and multiuser operating systems. Notable developments included Digital Equipment Corporation's (DEC) PDP series, which ran operating systems like OS/8 and Multics, the latter being the precursor to UNIX, developed at AT&T Bell Labs in 1969. Operating System Fundamentals 12  The 1970s saw the advent of microcomputers, which brought operating systems into the mainstream. Microsoft played a pivotal role by adapting 86- DOS into MS-DOS, which became the standard operating system for IBM PCs. MS-DOS's success was followed by the introduction of Apple's Macintosh in 1984, which featured a graphical user interface (GUI) and superior memory management. In response, Microsoft developed its own GUI, leading to the release of Windows in 1985. Over time, both Windows and macOS evolved into sophisticated operating systems, with Linux emerging as a strong contender, particularly in data centers. Today, operating systems provide essential interfaces between application programs and hardware, with Windows dominating business desktops, while Linux leads in server environments. Operating Approximate Bits Comments System Date First widely used multiuser, UNIX 1968 8 multitasking operating system for (Bell/AT&T) minicomputers First operating system that allowed serious business work on small personal computers. VisiCalc, a spreadsheet CP/M 1975 8 application released in 1978, was the first business calculation program for CP/M, and to a large extent made CP/M a success. First operating system for the very successful IBM PC family of computers. Lotus 1-2-3 was to MS-DOS 1980 16 MS-DOS in 1981 what VisiCalc was to CP/M. Also in 1981, Microsoft introduced the first version of Word for the PC. PC DOS 1981 16 IBM version of Microsoft MS-DOS The first widely distributed operating system that was totally Mac OS 1984 16 graphical in its user interface. Also, Mac OS introduced the use of a mouse to PC-based systems. Operating System Fundamentals 13  Operating Approximate Bits Comments System Date Mac OS implemented cooperative Mac System multitasking so that more than 1987 16 Software 5 one application could be run at one time. Mac OS was significantly Mac System 1988 16 stabilized and was also adapted Software 6 to run on portable computers. First usable version of a graphical Windows 3.0 1990 16 operating system for the PC Linus Torvalds made the first Linux 0.01 1991 16 version of Linux available through an FTP download site. Mac OS was redesigned to have a Mac System 1991 32 new interface, more applications, Software 7 and to use 32-bit addressing. The first actual distribution of MCC Interim Linux was offered through the 1992 16 Linux University of Manchester in England. Windows for First version of Microsoft Workgroups 1993 16 Windows with peer-to-peer (Windows 3.11) networking support for the PC Microsoft’s first attempt to bring a true 32-bit, preemptive multitasking operating system Windows NT with integrated network (New 1993 32 functionality to the world of Technology) personal computing. Windows NT was later offered in a Workstation version and a Server version. Linux kernel version 1.0 was Red Hat Linux, released, as were the first SUSE, and the 1994 16/32 distributions of Red Hat Linux and Linux kernel 1.0 SUSE Linux. Windows 95 1995 16/32 An upgrade to Windows 3.x, mostly 32-bit code, with a much improved user interface and increased support for hardware. It Operating System Fundamentals 14  Operating Approximate Bits Comments System Date offered native support to run 32- bit applications and many networking features. Windows 95 represented a different direction than Windows NT because it was intended to provide backward compatibility for 16-bit applications, and it continued to allow applications to directly access hardware functions. Implemented many bug fixes to Windows 95, more extended Windows 98 1998 32 hardware support, and was fully 32-bit The GNOME 1.0 desktop (similar in function to Windows) became GNOME 1.0 1999 16/32 available as free software and desktop grew to become one of the most popular UNIX/Linux desktops. A major revision of the Windows NT operating system; Windows 2000 was much faster and more reliable than Windows NT. The Windows 2000 kernel contained Windows 2000 2000 32 more than twice as many lines of code used in Windows NT. Windows 2000 came in several versions, including Professional, Server, Advanced Server, and Datacenter. Microsoft’s operating system Windows upgrade of Windows 98, Millennium 2000 32 designed specifically for the Edition (Me) home user, with improved multimedia capabilities. Mac OS X 2001 32 Introduced as a significant departure from the earlier Mac OS versions because it was rewritten to have UNIX-based Darwin as the foundation for the operating Operating System Fundamentals 15  Operating Approximate Bits Comments System Date system code. Updated versions of the OS continue to be issued, with the Mojave version (macOS 10.14) being the most current at this writing. Enabled compatibility with Plug Linux kernel 2001 32/64 and Play devices, including USB 2.4 devices The successor to Windows Me and Windows 2000 Professional, available in four editions: Home, Professional, Tablet PC, and Media Center. The Home Edition was a 32-bit system that focused on home use for photos, music, and other multimedia files. The Professional Edition, available in 32-bit and 64-bit versions, was intended for office and Windows XP 2001 32/64 professional users who needed more computing power and extensive networking capabilities. The Tablet PC Edition was tailored for tablet PCs that use speech and pen capabilities and offered great mobility, such as native wireless communications. Finally, the Media Center Edition was for enhanced digital media use involving television, audio, video, and graphics. Windows 2003 32/64 Available in Standard Edition, Web Server 2003 Edition, Enterprise Edition, and Datacenter Edition, this operating system was designed as a server platform for Microsoft’s.NET initiative, which integrated all types of devices—PCs, handheld computers, cell phones, and Operating System Fundamentals 16  Operating Approximate Bits Comments System Date home appliances—for communications over the Internet. Provided support for larger file system storage, new CPUs, more Linux kernel 2003 32/64 stable 64-bit CPU support, and 2.6 support for many more simultaneous users Introduced a newer security philosophy that employed a restricted user account control Windows Vista 2006 32/64 mode. Came in five editions: Home Basic, Home Premium, Business, Enterprise, and Ultimate. An interim release of Windows Server 2003 for compatibility with Windows Vista and to add new Windows 2006 32/64 features, particularly for medium- Server 2003 R2 sized and large organizations. Offered the same editions as Windows Server 2003. Employed the new security philosophy begun with Windows Vista and extended security for servers in part by offering greater Windows 2008 32/64 modularity to achieve a smaller Server 2008 attack profile. The main editions included Standard, Enterprise, Datacenter, Web, and HPC (High Performance Computing). Dropped support for PowerPC Mac OS X 2009 32/64 processors and switched to using Snow Leopard only Intel processors Windows 7 2009 32/64 Employed enhanced security features, with fewer headaches and stumbling blocks for the user, compared to Windows Vista. Offered many new desktop features. The editions included Operating System Fundamentals 17  Operating Approximate Bits Comments System Date Home Basic, Home Premium, Professional, Enterprise, and Ultimate. An interim release for Windows Server 2008 that included built-in compatibility with Windows 7. It had desktop changes similar to Windows those in Windows 7. Offered the 2009 64 only Server 2008 R2 same versions as Windows Server 2008. Microsoft’s current plans are only to develop new operating systems for 64-bit computers. Mac OS X Lion 2011 32/64 Introduced the Launchpad feature Included automatic Linux kernel defragmentation, improvements 2011 32/64 3.x to container support, and better driver support Added the popular iMessage app Mac OS X found on iOS and the Notification 2012 64 Mountain Lion Center. Dropped support for 32- bit Intel processors. Windows 8 was Microsoft’s first attempt to unify the mobile and desktop computing space. The touch-centric interface was not well accepted; to mollify users, Windows 8/8.1 2012/2013 32/64 Microsoft quickly released Windows 8.1, which walked back some of the disliked user interface changes from previous Windows versions. Windows 2012/2013 64 only Windows Server 2012 was Server 2012/R2 released along with Windows 8 and had the same user interface problems. Windows Server 2012 R2 was released along with Windows 8.1. Windows Server 2012/R2 made substantial Operating System Fundamentals 18  Operating Approximate Bits Comments System Date enhancements to its virtualization engine, Hyper-V, and added cloud-centric features. Windows Server 2012/R2 had Standard and Datacenter editions along with Foundation and Essentials. Enterprise edition was later dropped. Mac OS X 2013 64 only Mavericks Mac OS X 2014 64 Yosemite Added support for live patching of Linux kernel the kernel, primarily aimed at 2015 32/64 4.x installing security updates without requiring a reboot Mac OS X El 2015 64 only Capitan Windows 10 finished walking back the user interface problems of Windows 8 while providing a single OS that worked well on the Windows 10 2015 32/64 desktop as well as on touch- centric mobile devices like the Microsoft Surface. Speculation is that Windows 10 may be the last named version of Windows. macOS Sierra 2016 64 only Windows Server 2016 emphasizes virtualization, flexible storage solutions, and cloud computing, and includes a version Windows called Nano Server that has a 2016 64 only Server 2016 very small footprint for embedded and virtual deployments. Microsoft support for containers was first introduced in Windows Server 2016. Operating System Fundamentals 19  Operating Approximate Bits Comments System Date macOS High 2017 64 only Sierra Released in late 2018, Windows Windows Server 2019 focuses on 2018 64 only Server 2019 integration with Microsoft Azure, containers, and virtualization. macOS Mojave 2018 64 only Adds energy-aware scheduling, Linux kernel 2019 32/64 which is of primary importance in 5.x mobile devices macOS 2019 64 only Catalina Operating System Fundamentals 20