32-bit disk access

From Wikipedia, the free encyclopedia

32-bit Disk Access refers to a special disk access and caching mode available in older, MS-DOS-based Microsoft Windows operating systems. Sometimes enabling this mode would break older applications of the day. The term 32-bit refers to the usage of native, protected mode 32-bit drivers by the Windows kernel instead of the real mode 16-bit drivers included in MS-DOS.

Windows 3.1 had an option in its 386 Enhanced Control Panel that would enable 32-bit read & write access in 386 enhanced mode. Usually, 32-bit read could be safely enabled, but 32-bit write had issues with a number of applications. 32-bit Disk Access was the feature that made it possible to page MS-DOS applications to disk. Without it, if the real mode disk code (the Int 13h handler) was paged out, the virtual DOS machine would loop forever.

Windows 95, Windows 98, and Windows Me use native, protected mode 32-bit disk drivers during normal operation. However Safe Mode uses MS-DOS real mode disk drivers instead. Real mode MS-DOS drivers could also be used during normal operation for disk peripherals for which Windows did not have native drivers.

Windows NT, and therefore Windows 2000, Windows XP and later always have 32-bit disk drivers active, cannot use MS-DOS drivers at all, and the expression is not used for them.