Windows 98 System File Extensions

Microsoft Windows 98 utilized a hybrid 16-bit and 32-bit architecture bridging MS-DOS and the Windows graphical environment. To boot the operating system, load hardware drivers, maintain registry settings, and manage dynamic libraries, Windows 98 relied on a distinct collection of core system file extensions.

.SYS (System and Real-Mode Drivers)

The .SYS extension was critical during the initial boot phase and for low-level device management. Files like IO.SYS and MSDOS.SYS initialized the hardware and provided the MS-DOS core required to launch Windows. Additionally, CONFIG.SYS processed startup configuration directives, while device-specific .SYS files acted as real-mode drivers for hardware components.

.VXD (Virtual Device Drivers)

Virtual Device Drivers (.VXD) were the cornerstone of 32-bit protected-mode hardware management in Windows 98. These files allowed the operating system to manage hardware resources directly and virtualize them for multiple running applications, replacing older real-mode drivers and significantly improving system stability and speed.

.DAT (Registry Data Files)

The Windows 98 Registry replaced most legacy text-based configuration files. The registry database was stored primarily in two protected binary files: SYSTEM.DAT (containing hardware and machine-wide settings) and USER.DAT (storing user-specific configurations, desktop layouts, and application preferences).

.CAB (Cabinet Files)

Cabinet files (.CAB) served as compressed system archives holding the core operating system installation components. Windows 98 kept these archives on installation media and within local backup directories (such as C:\WINDOWS\OPTIONS\CABS) so the system could extract necessary drivers and system utilities without prompting for an installation disc.

.INI (Initialization Files)

Carried over from Windows 3.x for backward compatibility, .INI files contained plain-text configuration settings. Files like SYSTEM.INI defined display drivers, sound parameters, and core Windows settings, while WIN.INI managed user environment settings and desktop appearance prior to full registry adoption.

.INF (Setup Information Files)

The .INF extension designated plain-text installation scripts used by Windows 98 to detect, configure, and install device drivers and operating system updates. They detailed the specific registry modifications, file copy operations, and driver dependencies required for newly detected hardware.

Dynamic Link Libraries (.DLL) housed shared executable code and resources that multiple system processes utilized simultaneously. In Windows 98, core system DLLs—such as KERNEL32.DLL, USER32.DLL, and GDI32.DLL—managed memory allocation, input processing, and user interface graphics.

.DRV (Legacy Device Drivers)

Carried over from 16-bit Windows environments, .DRV files functioned as hardware drivers for components such as video adapters, sound cards, and mice. While largely superseded by .VXD files in Windows 98, they remained present for legacy hardware compatibility.

.PWL (Password List Files)

Password List (.PWL) files were encrypted system files stored in the Windows directory. They cached user network credentials, shared folder passwords, and Windows logon details for individual user profiles.