2. Microsoft Window 9X Operating System Richard Goldman © February 28, 2001

3. Operation of Windows 9X Windows 95 Windows 98 Windows Me

4. Hardware Windows 9X Hardware The computer hardware layer is all the physical components and devices that makeup or are attached to the computer. The main components of a computer are: System Board CPU Main Memory Chip Set Disk Drives Monitor and Printer Keyboard and Mouse

5. BIOS Hardware Windows 9X BIOS Phoenix The System BIOS chip contains small programs called device drivers that allow the software to communicate with the computer’s hardware. Many of the other devices have BIOS chips also. These BIOS chips identify the device they are on and may contain additional drivers. When the computer is first turned on, the System BIOS: locates all the devices attached to it, loads a driver into memory for each device, and performs a brief test of each device (POST).

6. BIOS Hardware Windows 9X DOS DOS Phoenix IO.SYS When the BIOS completes the POST it locates and runs the Boot Record on the default drive. The Boot Record locates and runs IO.SYS, also on the default drive. IO.SYS loads the DOS core components. Then IO.SYS runs CONFIG.SYS and AUTOEXEC.BAT, if present, to provide support for legacy software or custom configuration. IO.SYS runs WIN.COM.

7. Win 9X Core BIOS Hardware Windows 9X Core DOS UserGDIKernel Phoenix IO.SYS WIN.COM loads the Virtual Memory Manager ( VMM32.VXD) and the required Windows VxDs (real mode static device drivers) plus drivers listed in the [386 Enh] section of SYSTEM.INI. The VMM then loads the dynamic device drivers. The VMM loads the remainder to the Kernel, the User, and the GDI. Window then switches from 16-bit Real Mode to 32-bit protected mode. VMM Virtual Memory Manager IFS Installable File System DriversConfig. Mgr. Finally EXPLORER.EXE is run to provide a GUI shell. Start

8. Win 9X Start Core UserGDIKernel VMM Virtual Memory Manager IFS Installable File System DriversConfig. Mgr. BIOS Hardware Windows 9X Virtual Machines DOS Phoenix IO.SYS, MSDOS.SYS, COMMAND.COM Windows 9X creates a System Virtual Machine for all Windows applications. Each 32-bit Windows application runs in its own memory space within the System VM. 16-bit Windows applications share a memory space in the System VM. System VM DOS VM 32-bit Win App WOW 32-bit Win App 16-bit Win App DOS App DOS VM DOS App Each DOS application is given its own VM.

9. Win 9X Start Core UserGDIKernel VMM Virtual Memory Manager IFS Installable File System DriversConfig. Mgr. BIOS Hardware Windows 9X Core Functions DOS Phoenix IO.SYS, MSDOS.SYS, COMMAND.COM The Kernel provides basic operating system functions: Load and execute programs Memory management System VM DOS VM 32-bit Win App WOW 32-bit Win App 16-bit Win App DOS App DOS VM DOS App The User component controls the user interface – keyboard, mouse, etc. The GDI component manages the graphics output to the screen and printer. 16-bit Win App 32-bit Win App DOS VM DOS App File input/output