What is an operating system 2

7 PC operating systems

7.1 MS-DOS

From today's perspective, MS-DOS (Microsoft Disk Operating System) is out of date; But if you take into account the hardware conditions of the first PCs, it was designed quite sensibly at the time. The most important properties in brief:
  • for 16-bit processors (8086 and higher)
  • for memory area up to 1 MByte (real mode)
  • command line oriented
  • Single-user, single-tasking operating system
  • hierarchical file system
  • special hardware can be integrated via drivers
  • System calls do not reentrant
  • Devices only rudimentarily integrated into the file system
  • very simple command language

MS-DOS consists of several parts (= modules) that are located in a reserved area on the hard disk or floppy disk and are loaded and activated by the computer in the main memory when the system is started.

    This part is also called BIOS (Basic Input / Output System). It contains all parts of DOS that deal with the physical devices. Every time DOS accesses the keyboard, printer, hard disk or screen, this module becomes active. In addition to the device routines, IO.SYS also contains the routines for initializing DOS.
    This module contains the device-independent system routines and the disk and file management. The user programs also access these routines. MSDOS.SYS works closely with IO.SYS. The routines of IO.SYS are called every time the device is accessed. When this part of MS-DOS is started, the CONFIG.SYS file is also evaluated and the device drivers recorded there are loaded.
    This is the so-called command interpreter, which accepts the input of the user and then executes the desired command. Simple and frequently used commands are built directly into the command interpreter. The command interpreter also processes the batch files.

DOS-based applications often break through the above. Shell structure (partly because the BS is unable to provide the desired services). In many cases, the hardware of the PC is accessed directly (down to the register level). Therefore, there are sometimes incompatibilities. On the other hand, you can really do "everything" with the hardware under DOS, e.g. B. the integration of interrupt service routines in your own programs or device drivers.

7.2 Windows (Version 3.x)

With Microsoft Windows, an operating system extension with a graphical user interface for Intel PCs was brought onto the market for the first time. In terms of its properties, version 3 roughly corresponds to the Apple Macintosh system (Motorola processors). Windows is based on DOS. The properties in brief:
  • 32-bit addressing in protected mode (386/486 / Pentium)
  • cooperative multitasking
  • Graphical user interface
    • Control via mouse (pointer device)
    • Desktop as a system environment
    • Window as a work surface
    • Pull-down menus and scroll bars
    • Symbols (icons) for programs and data
    • Dialog boxes, buttons, sliders, ..
    • Interface for programs (GDI = Graphics Display Interf.)
  • uniform device drivers on which the programs are based
  • Extension of the system calls (API = Application Program Interf.)

Windows programs are based on GDI and API. The advantage is that all programs can be programmed independently of the device and are based on the drivers for screen, printer, CD-ROM, etc. - an advantage for application developers. For these, Microsoft has also issued guidelines for the user interface and menu design (CUA = Common User Access), which, however, are not adhered to as consistently as is the case with Macintosh software (where the operation of the programs is really completely uniform).

So-called "Dynamic Link Libraries" (DDLs) have been introduced in order to keep programs as small as possible and to allow several programs to access commonly used subroutines. These code libraries are reloaded as required.

The first steps in object-oriented work have been introduced with "drag-and-drop". If a file icon (e.g. a document) is dragged onto the icon of its generating program (e.g. a text editor), this program starts automatically to process this file. With the Macintosh, it is sufficient to "click" on the document with the mouse.

For data exchange between the programs, on the one hand the clipboard (clipboard), which supports the Windows formats for text, graphics, etc., on the other hand OLE (Object Linking and Embedding). OLE is not supported by all applications. A reference to the desired object (data + program for creating it) is entered here. If then z. If, for example, a picture is referenced in a text, the processing application starts automatically.

DDE (Dynamic Data Exchange) goes one step further. Changes in the original data are automatically transferred to all files in which reference is made to the object.

Cooperative multitasking allows you to work with several programs at the same time, but only one application is always active. Only simple services such as B. serial data transmission or print output continue to run in the background. Time-critical applications - which can only be about things as simple as data transmission or recording of measured values ​​- can cause problems. This can sometimes be remedied by changing the priority. Applications that do not "cooperate" (e.g. crash of a DOS program in the so-called DOS window) can paralyze the entire system.

The "Windows for Workgroups 3.11" extension also provides basic network support. It is a peer-to-peer network in which resources from another computer in the network can be used from each computer.

7.3 Windows 95

With the development of Microsoft's Windows 95, the right step was taken towards stability and user-friendliness. Windows 95 is the first 32-bit Microsoft Windows operating system for the mainstream PC. The old Windows versions had the disadvantage that they only ran on an MS-DOS basis, so it was not an operating system, but rather a graphical user interface that had to struggle with the DOS memory limits.
Windows 95, on the other hand, is a full-fledged operating system that comes with MS-DOS 7.0, but can work just as well without DOS. It has an interface that no longer works program-related but object-related, supports preemptive multitasking, includes an improved file system that allows long file names and has plug & play functionality that allows hardware components to be changed faster and more conveniently. Windows 95 can also be installed on a PC with a 386SX CPU and 4 Mbytes of main memory, but smooth work is only achieved with a PC with a Pentium CPU, 16 Mbytes of RAM and at least a 1 GByte hard disk, more main memory can increase the processing speed considerably, 32 Mbytes or more are recommended, especially when using extensive Office packages. To use the sound functions of Windows 95, you need a sound card in the computer.

Windows 95 supports full 32-bit protected mode versions of TCP / IP, IPX / SPX and NetBEUI, so that the client can access a NOVELL NetWare / IntraNetWare or Windows NT server. Support of several simultaneous communication protocols allow network connections of different types to be maintained at the same time. This enables parallel work in a NetWare network via IPX and a Unix network via TCP / IP. The embedded network clients for NetWare, Windows NT Server and Microsoft Exchange Server ensure that the user only has to log on once. A DF network (RAS, Remote Access Services) enables users to be connected quickly and easily to frequently used networks while on the move.

In the previous Windows versions, the program settings and Windows hardware drivers were managed in the so-called INI files in the Windows directory. Windows 95 now manages its own database (registry) for the INI files (in order to remain compatible with 16-bit applications), in which Windows 95 and 32-bit programs store information. It enables user-specific settings, such as individual settings for the desktop or network access, and contains hardware-specific settings for the PC. It provides system policies with which the system administrator can monitor the configuration and define user settings. The automatic hardware detection makes it easier to upgrade and expand the PC, especially with modern components based on the Plug'n'Play (PnP) standard. As soon as a new component is integrated into the system, Windows 95 recognizes this and suggests installing the driver. The support of the dynamic connection of PC cards (the former PCMCIA cards) allows notebook owners, for example, to plug the network PC card into the PC card slot while it is running (online) and to access the network directly.

The properties in brief:

  • no more DOS as "underlay", but DOS 7.0 as "DOS window"
  • preemptive multitasking
  • 32-bit operations
  • Drivers run in protected mode (memory above 1 Mbyte)
  • better memory protection of the applications
  • Network integration (IPX / SPX from Novell, TCP / IP, NetBEUI)
  • Multimedia interface (video and sound)
  • dynamic cache management (less disk access)
  • Folder (any nesting levels of applications)
  • Links and shortcuts (data <--> program)
  • File manager improved / extended (Explorer)
  • 'Plug & Play': automatic detection and installation of hardware components
  • Auto configuration (no more setup when changing hardware)
  • Improved user interface Instead of the program manager, now a 'taskbar' to start the program, icons for programs / links directly on the desktop, context-related pop-up menus via right mouse button.
  • long filenames
  • Configuration database
  • User profiles

7.4 Windows 98

Windows 98 includes countless detail improvements as well as a new user interface, which should make working with a Windows 98 PC much easier. New wizards and utilities make systems more reliable and easier to manage. The main innovations are:
  • FAT32
    FAT32 as the standard file system. FAT32 is an improved version of the FAT file system that allows hard drives with a capacity of more than 2 GB to be formatted as a single drive. FAT32 was previously only supported by the Windows 95 OEM version.
  • Improved power management
    Support for the Advanced Configuration and Power Interface (ACPI). ACPI is an open industry specification proposed by Intel, Microsoft and Toshiba, in which hardware interfaces are defined that enable standardized power management by the operating system for all components of a PC system.
  • Disk Optimization Wizard
    With the help of defragmentation, it increases the loading speed of the applications and the access to the files that are used most frequently. To do this, the wizard creates a log file that records which programs are used most frequently. After this file has been created, the "Optimizing Disk Wizard" can save the files associated with these frequently run programs one after the other on the hard drive. This continuous arrangement enables applications to run much faster.
  • Windows system update
    It's a new web-based service (in the form of an ActiveX control) that searches the system and determines what hardware and software is installed. It then compares this information with a back-end database and determines whether newer drivers or system files are available. If so, the service can install the new drivers automatically. The user can fully configure this process.
  • System file check utility
    This utility is an easy way to ensure that Windows 98 system files have not been altered or damaged. It also provides a simple method for restoring the original versions of changed or missing system files.
  • Win32 Driver Model
    This is an entirely new model for drivers that work on both Windows 98 and Windows 2000. WDM enables the use of a single driver for both operating systems for some common device types (e.g. USB and IEEE 1394). WDM was implemented by adding certain NT core services to Windows 98 using a special virtual device driver (NTKERN.VXD). In this way, Windows 98 is able to support old drivers without restrictions and at the same time enable the use of new WDM drivers.
  • integrated internet user interface
    This makes Internet access an integral part of the user interface (which is why this feature was already a concern of the courts). The user no longer has to learn how to operate multiple environments. With this universal program, local, network, intranet and internet data can be viewed in the same way.

7.5 Windows NT

Windows NT (New Technology) is a server-based multitasking operating system, i.e. with network support. Since Windows 95 or IBM's OS / 2 also support network operation, the target group is quite indifferent. An undeniable advantage, however, is that it is designed to be portable and can thus be implemented on different processors (Intel, Mips, DEC Alpha, etc.), which is not the case with any of the other OS presented except Unix. Applications can thus be created with source code compatibility. With NT, only the server application is currently of interest. NT 3.x workstations can do about the same as Windows 95 computers. The properties that go beyond "normal" Windows are:
  • preemptive multitasking
  • Division of programs into threads
  • suitable for multiprocessor systems
  • virtual memory management (up to 4 GB per process)
  • User administration, access rights, authentication
  • Support of large disks (up to 17,000,000 GB)
  • Support of various file systems (FAT from DOS, HPFS from OS / 2, NTFS from NT)
  • File system NTFS (NT File System)
    • Access rights
    • Fault tolerance (crash recovery)
    • Links, transaction-oriented access
    • long file names, distinction between upper and lower case
  • dynamically loadable device drivers
  • Network support (also for Novell, TCP / IP, OS / 2)

The system is well structured. The base is formed by three layers:

  • Hardware Abstraction Layer (HAL)
  • core
  • NT Executive (system services)

Subsystems that provide various operating system emulations are based on this. For DOS, OS / 2 or Windows applications, a separate, isolated 32-bit subsystem is created for each. Faulty programs or violation of access rights does not affect the work of the server. All network access is handled by the "Advanced Server", a higher-level administrative entity.

Configuration data is not stored in individual files, but in a single configuration database. The system and the drivers use this database. During the boot process, the system checks the function of all components.

The successor Windows NT 4.x is the powerful 32-bit operating system from Microsoft. It is specially optimized for network operation in connection with the client-server concept. Microsoft sells Windows NT in two versions, the Windows NT Server and the Windows NT Workstation. Both versions are supplied on separate CD-ROMs. The Windows NT server CD-ROM is intended for the construction of a complete NT network server, the Windows NT workstation CD-ROM can be used to equip workstation PCs with the Windows NT workstation system. Windows NT 4.0 presents itself in the interface of Windows 95, but has a completely different internal structure.

Microsoft Internet Explorer (web browser) is integrated in Windows NT 4.0 and the Internet Information Server (IIS, web server) is also integrated in Windows NT Server. The Internet Information Server allows you to set up your own web server with the services WWW, Gopher and FTP. This service integrates seamlessly into Microsoft's back office strategy. Windows NT 4.0 contains a DNS server (Domain Name Service) which was often missing in the old Windows NT 3.51 version. With the Remote Program Load (RPL) it is possible to boot diskless workstations (without hard disk) under Windows95 from the Windows NT server. Database connections via ODBC can be implemented via the Internet server. In addition to the free Internet Explorer and the Exchange Client, important highlights of Windows NT 4.0 are the support of a large number of new drivers, higher graphics performance by relocating parts of the GDI to the kernel, setting up hardware profiles and a DirectX interface for games on Windows NT to make it run.

Windows NT supports both preemptive multitasking and multithreading as well as multiprocessing (distribution of program parts over several CPUs). It is scalable to up to 32 CPUs (Windows NT workstation can max.2 CPUs address, for Windows NT Server there are different licenses depending on the number of processors). 4 GB of RAM are supported per system, each application can be assigned up to 2 GB of virtual memory. The system supports data storage of up to 402 million terabytes. Microsoft specifies at least a 486 CPU, 16 MByte RAM and a 500 MByte hard disk as system requirements. However, it has been shown that working with acceptable performance is only possible with a Pentium 100 CPU, 64 MB RAM and a 1 GB hard disk. Windows NT supports the processor platforms Intel x86 / Pentium, and DIGITAL Alpha AXP / 21x64. The software for both platforms is contained on the CD and accommodated there in different directories. Windows NT can run applications written for IBM's Presentation Manager (up to version 1.3) and POSIX 1003.1.

The most widespread is Windows NT on the Intel architecture. Windows NT on Alpha architecture is mostly used when very high CPU or I / O performance is important. However, the alpha version is no longer being developed.

The scope of delivery includes support for the TCP / IP, NetBEUI, IPX / SPX, DLC and AppleTalk protocols. Windows NT contains Telnet and FTP clients as well as an FTP server service in the server version. The Dynamic Host Configuration Protocol (DHCP) enables the dynamic establishment and management of TCP / IP addresses. Windows Internet Naming Service (WINS) assigns names to the TCP / IP addresses. This makes it easier for the administrator and user to work in a TCP / IP network. It is also easily possible to integrate Windows NT into a NetWare network. The Client Service for NetWare (CSNW) enables access to the file and print services of a NetWare 3.x server. The Gateway Service for NetWare (GSNW) provides workstations on the Windows NT Server network with access to NetWare servers. Migration tools are also offered, which take over the user information and directories. It is thus possible to take over or control the complete user administration of NetWare with a Windows NT server.

Windows NT supports remote access with the protocols NetBEUI, IPX / SPX and TCP / IP; this can be done via ISDN, X25 or analog telephone lines. As a client, Windows NT allows Unix via PPP / SLIP, NetWare, LanRovers, Windows 3.x, Windows95 and LAN Manager. This Remote Access Service (RAS) allows up to 256 simultaneous connections. With RaRAS (Routing and Remote Access Service) Microsoft offers a software-based multi-protocol router for Windows NT Server 4.0. RaRAS supports routing of TCP / IP and IPX. RIP and OSPF are supported as routing protocols, as well as static routing. For authentication via PAP / CHAP, RaRAS uses Windows NT domain user authentication. RADIUS clients are also supported. The routing table manager is a central component of RaRAS. The routing tables are managed here. A graphical user interface is available for configuration and management.

Windows NT is a multitasking operating system, but unlike Unix, it is not a multiuser operating system. The American software manufacturer Citrix Systems had taken on this deficit. In 1992, Citrix and Microsoft signed an agreement on a strategic partnership for the development of the multiuser NT WinFrame. WinFrame is the basis for "Application Publishing", a new way for modern client / server architectures in the PC environment. The basic idea of ​​application publishing is not new. The principle is largely reminiscent of Unix-based networks with X-Window terminals. With application publishing, the applications do not run on the individual workstation PC, but on the server. The workstation computer only receives the window display via the network, so it needs neither installed applications nor high computing power or memory expansion.

Microsoft Windows 2000, previously known as Windows NT 5.0, has been expanded to include a number of new features and functions. This includes the areas of administration, scalability and expandability as well as storage and hardware management. Microsoft will offer Windows 2000 like NT in three versions: Windows 2000 Professional corresponds to Windows NT Workstation, Windows 2000 Server corresponds to NT Server and the NT Enterprise Edition will continue as Windows 2000 Advanced Server.

Microsoft Windows 2000 implements Active Directory as a central platform that simplifies access and management of network and system resources. Further features are centralized configuration management and the configurable and expandable Microsoft Management Console (MMC).

Windows 2000 supports max. 4 GByte physical memory, with 64-bit CPUs (Digital Alpha, Intel Merced) 32 GByte can be addressed. With the Microsoft Cluster Server, two servers can work together. The devices monitor each other in order to maintain operation without interruption in the event of a server failure. During normal operation, the servers can share the workload among themselves in order to achieve higher productivity.

The NTFS file system now also implements a quotation with which the maximum available disk space can be determined for the users. The NTFS extension EFS (Encryption File System) enables the encryption of sensitive data at file or directory level. Because of the export restrictions for cryptographic processes, however, it is a matter of so-called "weak encryption".

Plug-and-Play is now also finding its way into Windows 2000. This then also enables the problem-free operation of PC cards in mobile computers. In addition, the expansion of the Windows Driver Model (WDM) is intended to ensure that identical driver software can be used in Windows 98 and Windows 2000.

7.6 OS / 2 (Version 3.0 - Warp)

OS / 2 in its first version (like Windows NT) was very "memory hungry" - and that at a time when PCs with 8 Mbytes of main memory were the exception. In the meantime the requirements are lower (4 MB) and at the same time the computers are better equipped. It is a stand-alone product that is not based on DOS or Windows. In contrast to Windows 95, it comes with a 'bonus pack' that contains almost everything for simple applications. The 'Works package' contains word processing, calculation, database, business graphics, scheduler, etc. A terminal program for data communication and fax software are also included. The properties in short:
  • preemptive multitasking
  • DOS and Windows run under OS / 2 (not included in the package)
  • 32-bit operations
  • shared libraries
  • graphical user interface (WPS)
  • Network integration (TCP / IP, LAN server)
  • Folder (any nesting levels of applications)
  • Links and shortcuts (data <--> program)
  • 'Plug & Play' (similar to Windows 95)
  • Work Place Shell (WPS) with a powerful script language
  • Start button bar (corresponding to Windows 95 taskbar) with subgroups
  • long filenames, efficient file system (HPFS)
  • Configuration database
  • Drivers for "exotic" hardware are sometimes missing

With the support of DOS and Windows, OS / 2 is less structured. What is new compared to the other systems are so-called 'sessions' - OS / 2 modules, each of which has its own virtual resources (keyboard, mouse, screen, printer, etc.). DOS and Windows applications are sealed off in the same way; these run in so-called 'Virtual DOS Machines' (VDMs) so that they cannot influence other applications.

The spread of OS / 2 suffered from the beginning that IBM sometimes pushed the product and sometimes swept it under the carpet. A second reason for the lack of acceptance was the new and different user interface from Windows and the fact that not all Windows software ran on OS / 2.

7.7 Unix (and derivatives)

Unix is ​​one of the oldest operating systems (just 25 years old). It was exemplary for other systems in many properties (DOS, Windows and OS / 2 also "copied" from UNIX). It is now available for almost every hardware platform. Actually, one has to speak of an operating system family here, because practically every workstation manufacturer delivers its own Unix, which differs a lot, at least in the user interface. However, there is a tendency here to overcome the variety of interfaces, as individual manufacturers have started to port their systems to third-party architectures. The Unix implementations can be summarized in two standards: Berkeley Unix (BSD) and AT & T's System V Release 4 (SVR4). The latter is currently in the process of gaining priority. Newly emerging Unix versions follow this standard. In general, if a program is written for one of the two standards, it can be ported to another system of the same standard without too much problems. There are also different standards for the user interfaces (GUI - Graphical User Interface) used. The newer ones all follow the X11 definition. The MOTIF definition, which is also based on X11, has been on the advance for a number of years. More and more Unix implementations are making use of this interface, while competitors such as OPENLOOK are on the decline.

The most important properties in brief:

  • UNIX is a portable, simply structured operating system
    • Multitasking OS (Multiprocessing OS)
    • Multiuser OS (multi-user OS)
    • conversational
  • UNIX is a tool kit
    • many hundreds of utilities
    • flexible: small tools can be created quickly
  • UNIX is suitable for upper-class microcomputers, mini-computers, mainframes
  • UNIX is terrible
    • Command names are cryptic (ls, pwd, cat, awk, grep, ..)
    • Motto 1: "No news is good news!"
    • Motto 2: "Who wants bad news?"
  • with graphical user interface (X Window) can be operated like Windows
  • UNIX is structured in layers
    • Shell (command interpreter) with a powerful script language
    • core
    • driver
  • Tasks of the core
    • Process scheduling
    • Process switching
    • Process communication
    • Manage file system
    • Input / output control
    • Device driver
    • Access control and billing
    • all system services for programming interfaces
  • The file system is structured hierarchically
    • long filenames
    • Normal files
    • Directories
    • Special files = device interface
    • Named pipes
    • Left
    • Each file has 12 independent protection bits

Network operation via TCP / IP has been possible with UNIX from the start. Most of the network services of other systems are based on the UNIX services. In particular, the 'Internet Connectivity', which is now on everyone's lips, is based on UNIX. So it is z. B. also possible to integrate disks of other computers over the network.

More than 90% of the code is programmed in C -> portable. Source code is also available for countless applications (for your own adjustments).

7.8 Linux

Linux is a freely available multitasking and multiuser operating system based on UNIX for systems with Intel processors. Linux was invented by Linus Torvalds and further developed by a large number of developers around the world. Linux was placed under the GPL, the General Public License, from the start. It can be freely distributed, used and expanded free of charge. Developers have an insight into all source codes and can therefore easily integrate new functions or quickly find and eliminate programming errors. Drivers for new adapters (SCSI controllers, graphics cards etc.) can be integrated very quickly. In the meantime, Linux has caught up with comparable UNIX implementations - it is often even more robust and stable than commercial products.

Linux can be obtained in two different ways: All the necessary parts can be downloaded from the Internet free of charge. It is easier to use a so-called distribution, these are offered by various companies and, in addition to a large number of applications, contain an installation program that considerably simplifies the installation of Linux. We recommend the distributions from RedHat and S.u.S.E.

Linux is now used successfully by millions of users worldwide. The user groups range from private users to training companies, universities and research centers to commercial users and companies who see Linux as a real alternative to other operating systems.

7.9 OS / 9

OS / 9 is a real-time operating system that was implemented on the Motorola 6809 processor 15 years ago and was later transferred to the 68000 processor family. In order to meet real-time conditions, its structure differs from other operating systems.

  • all programs are available as so-called 'modules'
  • all modules have the same structure and can be freely moved in the memory
  • OS / 9 can switch between RAM
  • and ROM area differ
  • When the system is started, modules are found automatically in the ROM
  • as many modules as possible are kept in the memory; therefore, OS / 9 systems can operate without mass storage
  • The operating system consists of four parts:
  • Kernel (only 26 KByte) with preemptive multitasking, basic functions for I / O, resource and process
  • and user management
  • File manager for random block devices (disk), sequential character devices, pipes and others.
  • Driver for I / O devices
  • Descriptors for OS, network and devices
  • Adaptation of the core to different hardware via initialization modules
  • Time slice procedure (10 ms) with priority assignment
  • Priorities are assigned dynamically (the process receives, for example, higher priority when an interrupt intended for it occurs (quick response!)
  • Access to the hardware only via the kernel
  • Shared libraries (similar to DLL in Windows), which are addressed via so-called trap handlers
  • Process communication via signals, events (= semaphores) and data modules
  • hierarchical file system
  • Graphical user interface on request (X-Window, MGR Window Manager, OS-9-Windows)
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