To end-users, MS-DOS appeared as an underlying component of Windows 95. For example, it was possible to prevent loading the graphical user interface and boot the system into a real-mode MS-DOS environment. This sparked debate amongst users and professionals over the question of to what extent Windows 95 was an operating system or merely a graphical shell running on top of MS-DOS. From an architectural stance, both viewpoints lack nuance.
When the graphical user interface was started, the virtual machine manager took over the filesystem-related and disk-related functionality from MS-DOS, which itself was demoted to a compatibility layer for 16-bit device drivers.[15] This contrasted with earlier versions of Windows which relied on MS-DOS to perform file and disk access. (Windows for Workgroups 3.11 could also largely bypass MS-DOS when 32-bit file access and 32-bit disk access was enabled.) Keeping MS-DOS in memory allowed Windows 95 to use DOS device drivers if suitable Windows drivers were unavailable. 16-bit applications that utilize DOS INT 21h calls are merely sent to a stub that goes to the equivalent 32-bit OS routine. Windows 95 is capable of using all 16-bit Windows 3.x drivers.
Using DOS applications in Windows 95 was much like 3.1, but DOS drivers are no longer needed for things such as mice, CD-ROM access, and sound card support (Windows' own drivers handle this task when running DOS applications). While HIMEM.SYS is still required to boot up Windows 95, EMM386 and other memory managers aren't and only need to be loaded for DOS applications that need them. In addition, CONFIG.SYS and AUTOEXEC.BAT settings (aside from HIMEM.SYS) have no effect on Windows applications. Most DOS games can run from within Windows 95, while 3.x normally was limited to application software (games tended to lock up Windows 3.x or cause other problems). Protected mode DOS programs were also runnable as Windows 95 provides p-mode emulation (these cannot be used in Windows 3.x at all). As with Windows 3.x, DOS applications that use EGA or VGA graphics modes cannot be run windowed and will be suspended by the OS if this is done (CGA and text mode programs can continue to run).
If F8 is pressed following the POST beep sound, a menu is pulled up allowing the user to continue starting Windows normally, exit to DOS, or start in safe mode. Straight DOS mode works just like in all previous versions; there is no 32-bit support and DOS drivers must be loaded for mice and other hardware.
A negative consequence of keeping MS-DOS around was that Windows had to do some work to keep DOS's internal data structures synchronized with those of Windows itself. When starting an application, even a native 32-bit Windows application, MS-DOS would momentarily execute to create a data structure (the program segment prefix) and it was even theoretically possible for MS-DOS to run out of conventional memory while doing so, preventing the application from launching.[16][page needed] Windows 3.x in fact allocated FIXED segments in conventional memory first, which can conflict. And since the segments were allocated as FIXED, Windows could not move them, which would prevent any more applications from launching. This was fixed in Windows 95.[citation needed]
Microsoft partially removed support for the outdated File Control Blocks (a relic of DOS 1.x and CP/M) in Windows 95 OSR B. FCB functions cannot write to FAT32 volumes, only read them.