Editing Windows 9x (section)

====Drivers====

[[Device driver]]s in Windows 9x can be virtual device drivers or (starting with Windows 98) WDM drivers. VxDs usually have the [[filename extension]] <code>.vxd</code> or <code>.386</code>, whereas WDM compatible drivers usually use the extension <code>[[.sys]]</code>. The 32-bit VxD message server (msgsrv32) is a program that is able to load virtual device drivers (VxDs) at startup and then handle communication with the drivers. Additionally, the message server performs several background functions, including loading the Windows shell (such as [[Explorer.exe]] or [[Progman.exe]]).<ref>{{Cite web|url=http://support.microsoft.com/?kbid=138708|title=Function of the Windows 32-Bit Message Server|website=Microsoft Help and Support|archive-url=https://web.archive.org/web/20070107132442/http://support.microsoft.com/?kbid=138708|archive-date=January 7, 2007|access-date=April 21, 2019}}</ref>

Another type of device drivers are <code>.DRV</code> drivers. These drivers are [[New Executable]] format and are loaded in user-mode, and are commonly used to control devices such as multimedia devices. To provide access to these devices, a [[dynamic link library]] is required (such as MMSYSTEM.DLL).

Windows 9x retains backwards compatibility with many drivers made for Windows 3.x and MS-DOS. Using MS-DOS drivers can limit performance and stability due to their use of conventional memory and need to run in real mode which requires the CPU to switch in and out of protected mode.

Drivers written for Windows 9x are loaded into the same address space as the kernel. This means that drivers can by accident or design overwrite critical sections of the operating system. Doing this can lead to system crashes, freezes and disk corruption. Faulty operating system drivers were a source of instability for the operating system.
Other [[Monolithic kernel|monolithic]] and [[hybrid kernel]]s, like [[Linux kernel|Linux]] and [[Architecture of Windows NT|Windows NT]], are also susceptible to malfunctioning drivers impeding the kernel's operation.

Often the software developers of drivers and applications had insufficient experience with creating programs for the 'new' system, thus causing many errors which have been generally described as "system errors" by users, even if the error is not caused by parts of Windows or DOS. Microsoft has repeatedly redesigned the Windows Driver architecture since the release of Windows 95 as a result.