The Operating System Ancillary Systems
All of the ancillary systems operate using 32-bit mode. Windows 98 comes with a collection of 32-bit file system drivers that support FAT16, FAT32, and ISO 9660 format CD-ROM discs, and the DVD Universal Disc Format.
The Process Scheduler is responsible for allocating system resources and provides pre-emptive multitasking by dividing the amount of time each application can have to access to the CPU and other system resources. These time slices are called threads. Thus the term multi-threaded can be applied to Windows 98. An application can have more than one thread open at a time, as a result, Windows 98 is known as a multi-threading, multi-tasking operating system.
File System Drivers. Like Windows 2000, Windows 98 offers support for the Windows Driver Model (WDM), allowing compatible devices to use the same driver for both operating systems. Its Plug-and- Play feature is much improved over Windows 95. WDM drivers can be categorized into one of several classes:
Device class drivers contain class-specific functions. These are used for classes of products like mice, joysticks, and keyboards.
Bus class drivers are available for both USB and IEEE 1394 buses. They work to speed up communications between the hardware layer and the minidrivers.
Minidrivers are hardware-specific and generally operate a class of devices operating on a specific type of bus. This class includes support for SCSI, USB, DVD, IEEE 1394, and network adapters. Minidrivers can be written to support multifunction cards like a video capture card that includes both video and sound functions on a single product. Both Windows 98 and Windows ME dynamically loads and unloads minidrivers as they are needed or released to save on memory and avoid usage conflicts. Ntkern.vxd is the operating system services layer for Windows 98 and Windows ME. This layer is always system-specific and allows the minidrivers to function with more than one operating system. Under Microsoft Windows NT, the operating system services layer is the hardware abstraction layer (HAL).
Virtual device drivers (VxDs) are 32-bit protected mode drivers responsible for managing a system resource. These drivers do not control the hardware device, but act as an interpreter between the hardware and the application, ensuring that only one system process controls the resource at any specific time. VxDs are only held in memory when they are actually in use. Some VxDs are also used with legacy hardware and software to allow them to function within the Windows 98 and Windows ME environment.
The Virtual Machine Manager (VMM) manages the system's virtual machine, the environment in which all system processes operate. In other words, it manages the key resources required by both applications and system processes. These include process scheduling, memory management, exception handling, and mapping access to the system BIOS, device drivers, and TSR programs.