Arquivo 386

.386 files are Virtual Device Drivers (VxDs) for Windows 386 Enhanced Mode, introduced with Windows/386 2.x in 1988. A VxD is a kernel-mode binary component that virtualizes a hardware device or OS service - such as a timer, keyboard, display adapter, or disk controller - so that multiple DOS applications running simultaneously can each believe they have exclusive access to the hardware.

Internally, a .386 file is an MZ DOS executable stub followed by a Linear Executable (LE) header. The LE header carries a VxD descriptor block identifying the device ID, version, and entry points for initialization, I/O port virtualization, and interrupt handling. Windows/386 2.x used an earlier proprietary W386 header format before the LE standard was adopted.

.386 VxDs run entirely in Ring 0 (kernel mode) with no memory isolation. This made them powerful but unstable: a faulty driver could crash the entire operating system. Windows NT used the WDM (Windows Driver Model) with proper kernel isolation from the start; Windows 98 SE began the transition, and Windows Me was the last consumer release to support VxDs. Windows XP and later cannot load .386 files at all - the VxD subsystem was removed.

The same virtual device driver role is also filled by .vxd files (functionally identical, different extension used for dynamic VxDs under Windows 95/98). Well-known examples include VSHARE.386, VFAT.386, and VTDAPI.386. These files are loaded automatically by the Windows kernel at boot or on demand; they cannot and should not be opened manually.