Restrictions

This section describes the few restrictions that apply to running applications under the 16-bit Windows subsystem.

• Direct access to floppy disk drives is supported. Direct access to a hard disk is supported, if the user is an administrator and no one else is using the disk at that time.
• All MS-DOS functions except task-switching APIs (application programming interface functions) are supported.
• Block mode device drivers are not supported. (Block devices are not supported, so MS-DOS IOCTL APIs that deal with block devices and SETDPB functions are not supported).
• Interrupt 10 function 1A returns 0; all other functions are passed to read-only memory (ROM).
• Interrupt 13 calls that deal with prohibited disk access are not supported.
• Interrupt 18 (ROM BASIC) generates a message that says ROM BASIC is not supported.
• Interrupt 19 will not reboot the computer, but will cleanly terminate the current virtual DOS machine (VDM).
• Interrupt 2F dealing with the DOSKEY program call outs (AX = 4800) is not supported.
• Microsoft CD-ROM Extensions (MSCDEX) functions 2, 3, 4, 5, 8, E, and F are not supported.
• The 16-bit Windows subsystem on an X86 computer supports Enhanced mode applications; it does not, however, support 16-bit VXDs (virtual device drivers). The subsystem on a non-X86 computer supports only Standard mode 16-bit applications.