Older Operating Systems

Transcription

1 Older Operating Systems Class Notes # 16 Microsoft Windows December 11, 2003 Windows 3.X Windows 3.X is not really an operating system, but also does not act like a normal application. Windows 3.X provides an operating environment, which provides support to application software, including cooperative multitasking and a GUI (Graphical User Interface). Windows 3.X is a middle layer that manages this multitasking environment by passing tasks to DOS one at a time. DOS manages its single tasking environment and relates to the hardware in single task fashion. Figure one illustrates the Windows 3.X operating system model. User Applications Software Windows 3.X Operating Environment DOS BIOS Device Drivers Hardware Figure 1: Windows 3.X layer view Windows 3.X is sometimes slow due to the complexity of the middle layer concept. There are problems where DOS and Windows 3.X applications tend to conflict with one another when sharing hardware resources. Therefore, Windows 3.X is prone to system crashes. Cooperative multitasking is not true multitasking and therefore the CPU is actually performing one operation at a time. The CPU is switching back and forth between applications so that more than one application can be loaded at the same time. There is only one active application run at one time and one or more inactive applications waiting in the background for the active application to relinquish (give up) control. Windows 3.X sometimes interact directly with hardware, such as when printing with one of its own printer drivers. In this case, Windows 3.X behaves as a true OS. But most of the time, Windows 3.X passes functions to DOS. DOS can choose to relate directly to the hardware, pass the hardware request to BIOS, or pass the hardware request to a device driver to be processed. 1

2 Windows 9X Windows 9X is closer to a true operating system but does not completely eliminate DOS. Windows 95 is the marriage of Windows 3.11 with an updated version of DOS known as DOS 7.0. Windows 95 also introduced an improved and more automated method of installing hardware devices called plug and play. Windows 98 includes several improvements, but is fundamentally the same operating system. The underlying DOS portion of Windows 98 is DOS 7.1. There are two additional upgrades to Windows 98, which are: Windows 98 second edition and Windows Millennium Edition. Windows 9x still has a DOS based core, uses many 16-bit programs, and must manage memory in the same fundamental way as DOS. However, Windows 95 introduced 32-bit programming, dynamically loaded device drivers, memory paging, networking, and many other features. Windows 9X claims to be backward compatible with older software written for DOS and Windows 3.X. Windows 9X uses cooperative multitasking when supporting 16-bit applications and preemptive multitasking when supporting 32-bit applications. Preemptive multitasking is where the operating system allocates CPU time to an application for a specified period, and then preempts the processing to give the CPU to another application. The result is that the computer appears to be performing true multitasking. Windows 9X architecture The Windows 9X architecture is made up of many components as shown in figure two. User Application Software Windows 9X User interface tools and 32-bit application shell CORE (User, Kernel, GDI) Registry VMM IFS Manager Configuration Manager WDM driver manager Hardware Figure 2: Windows 9X architecture 2

3 The core components of Windows 9X is the user, kernel, and GDI. Table one describes these components. Table one: Core components of Windows 9X Component Name Main files holding components Functions User User32.dll, User.exe Controls mouse, keyboard, ports, and desktop (position of windows, icons, and dialog boxes) Kernel Kernel32.dll, Krnl386.exe Handles the basis OS functions such as managing memory, file I/O, and loading and executing programs. GDI GDI32.dll, GDI.EXE Draws screens, graphics, and lines, and prints them A description of the other Windows 9x components are: The Installable File System (IFS) manager is responsible for all disk access. The configuration manager is responsible for the plug and play features of Windows 9X and other hardware configuration tasks. The Virtual Memory Manager (VMM) manages memory in a virtual machine environment. Win32 Driver Model (WDM) driver manager that is found in Windows 98 and not Windows 95, is responsible for managing device drivers. The registry, a hierarchical database that contains configuration information and hardware/software settings. DOS is a 16-bit operating system and therefore DOS only supports 16-bit drivers and application programs. Windows 3.X also only supports 16-bit applications, but does contain a small amount of 32-bit code. Windows 3.11 introduced VFAT, a 32-bit programming for disk access. Windows 9X contains some 16-bit code and some 32-bit code. Programs written in 32-bit code are faster than programs written in 16-bit code. Windows 9X supports VFAT, which is written with 32-bit code. Windows 9X support 16-bit drivers but prefers to run 32-bit drivers that are supplied with Windows 9X because: They are generally faster. 32-bit drivers can be stored in extended memory, thereby releasing more conventional memory to application programs. 32-bit drivers can be dynamically loaded (i.e. loaded into memory when they are needed and removed from memory when they are not). Virtual Machine You can think of a virtual machine as several logical machines within one physical machine. The virtual machine can support 32-bit and 16-bit Windows application programs, but DOS programs are executed within its own virtual machine. A DOS program expects to have direct control over hardware, including memory. If DOS uses 3

4 memory addresses not assigned to it, errors can occur in a multitasking environment. Therefore, Windows 9X provides DOS programs with its own logical machine. The DOS program is made to think that it owns the machine and can do whatever it want to the hardware. That s a virtual machine! Windows 9X Startup Process Windows 9X initially loads in real mode and then switches to protected mode. With DOS, the two-core real-mode system files responsible for starting up the operating system is IO.SYS and MSDOS.SYS. These two files remain in memory while the operating system is running. In Windows 9X, the initial startup process is real mode (IO.SYS is loaded and runs) and then switches to protected mode (IO.SYS is terminated and VMM32.VXD starts). The MSDOS.SYS is only a text file that contains some parameters and switches that can affect the Windows 9X boot sequence. There are five main stages to booting a PC with Windows 9X which is illustrated in figure three: Stage 1: BIOS startup. Startup BIOS begins and configures Plug and Play (PnP) devices. It performs POST and saves information for Windows configuration manager. Stage 2: DOS drivers, TSRs and Environmental settings. BIOS turns over control to IO.SYS which creates a real mode operating system environment. It automatically loads several drivers, sets several environmental variables, and executes any commands listed in CONFIG.SYS and AUTOEXEC.BAT. CONFIG.SYS and AUTOEXEC.BAT are typically not used since many of their commands are automatically executed by IO.SYS. However, for backward compatibility, any entries in these files are executed. IO.SYS checks MSDOS.SYS for boot parameters and automatically loads the following drivers if they are present: HIMEM.SYS, IFSHLP.SYS, SETVER.EXE, and DRVSPACE.BIN (or DBLSPACE.BIN). Stage 3: Static VXDs. The IO.SYS relinquishes control to the virtual memory manager (VMM23.VXD). The virtual memory manager terminates IO.SYS and loads static VXD device drivers. VXD is a virtual device driver that works with a virtual machine to provide access to hardware for software running in the virtual machine. Stage 4: Protected mode switchover and PnP configuration. VMM32.VXD switches to protected mode and loads configuration manager. Configuration manager uses any information that PnP BIOS might have saved for it, and loads the 32-bit dynamic device drivers (VXDs) for the PnP devices. Stage 5: Loading remaining components. With VMM32.VXD still in control, the three core components of Windows 9X are loaded, fonts and other associated resources are loaded. WIN.INI is checked and commands stored there are executed to allow for backward compatibility. Finally, any processes stored in the startup directory is executed. 4

5 Stage 1: BIOS bootstrap BIOS boots PC POST Plug and Play BIOS configuration Stage 2: DOS drivers and TSRs IO.SYS MSDOS.SYS and CONFIG.SYS COMMAND.COM and AUTOEXEC.BAT WIN.COM loads real mode components Stage 3: Real mode VXDs loaded (IO.SYS terminates) VMM32.VXD creates virtual machine Load static VXDs named in registry and SYSTEM.INI Stage 4: Shift to protected mode and Plug and Play configuratoin Load Plug and Play configuration manager Plug and Play loads dynamic device drivers (VXDs) Stage 5: Loading remaining components Loads: Kernel (kernel32.dll, krnl386.exe) GDI (gdi.exe, gdi32.dll) User (user.exe, user32.dll) fonts WIN.INI Shell and desktop are built In a network environment, logon prompt appears Startup directory is processed Figure 3: Windows 9X loading process 5

6 Real Mode DOS assumes that only one application or program would be running at one time, so it gave that program direct access to the memory addresses and the data in RAM that they pointed to. Also DOS was designed to pass segments of data to the CPU only at a time. These operations are collectively referred to as real mode. Therefore, real mode is single tasking program access to 1024 kbytes of memory addresses pointing directly to RAM using a 16-bit data path. Virtual Mode When an OS, that supports protected mode, allows a 16-bit program that is written to operate in real mode to run, this is called virtual real mode. In virtual real mode, the program thinks it is really working in a real mode environment. The program believes that: It is the only program running It has all memory available to it, all 1024kbytes of memory addresses that directly point to RAM It accesses data using a 16-bit data path. Real Mode Virtual Mode program program Memory map (0 to 1024k) Memory map (0 to 1024k) RAM OS manages memory 32 bit RAM and hard drive swap file Figure 4: Real mode and Virtual mode illustrations 6

7 Virtual Device Drivers Software written with 32-bit code is generally faster and takes up more memory than older software written in 16-bit code. Windows 9X offers many drivers written in 32-bit code that can replace the older 16-bit drivers written for DOS in real mode. The 32-bit drivers are called virtual device drivers or VXD drivers; they have.vxd or.386 file extensions and operate in protected mode. In order for Windows 9X to use older 16-bit drivers, it must provide a real mode environment for these drivers to operate in. The real mode environment is created by using entries in the CONFIG.SYS and AUTOEXEC.BAT files that is normally not required with Windows 9X. Plug and Play Plug and Play (PnP) is a set of design specifications for both hardware and software that is used for hardware installations. For a system to be PnP compliant, it has to meet these criteria: System BIOS must be PnP. Most system boards built after 1994 have PnP BIOS. All hardware devices and expansion cards must be PnP compliant. The OS must be Windows 9X or another OS that supports PnP. A 32-bit device driver (VXD) must be available. Windows 9X is a plug and play OS that provides two main services: resources management and run-time configuration. Resources management occurs at startup as system resources are allocated to devices. Run-time configuration is an ongoing process that monitors any changes in system devices. A device that is not PnP compliant is a legacy device. Legacy devices are not able to have their resources assigned to them by PnP. Legacy cards have DIP switches or jumpers on the card to set the system resources. This can sometimes cause resource conflicts between two devices. Windows uses four components in implementing PnP architecture: Configuration manager controls the configuration process of all devices and communicates these configurations to the devices. Hardware tree is a database built each time Windows 9X starts up that contains a list of installed components and the resources they use. Bus enumerator locates all devices on a particular bus and inventories the resource requirements for these devices. Resource arbitrator decides which resources get assigned to which devices. 7