Microsoft 32-bit disk access

32-bit Disk Access refers to a special disk-caching and writing mode available in 32-bit operating systems, that may or may not run purely 32-bit applications. Sometimes enabling this mode on older operating systems would break older applications of the day. The term 32-bit refers to the width of the data bus or how much data it can thransfer per machine cycle.

Windows 3.1

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 Int 13h handler was paged out, the virtual machine would loop forever.

Windows 9x

Windows 95, Windows 98, and Windows Me use protected mode disk drivers that are 32-bit in nature.

Safe Mode uses real mode disk drivers that disable native OS 32-bit disk access.

Other Operating Systems

Windows NT, and therefore Windows 2000, Windows XP and later always have 32-bit disk drivers active.

See also: 32-bit File Access

References

• Explanation of SMARTDRV & 32-bit disk access from Microsoft
• 32-bit in Windows 3.1 / 9x
• Windows driver support for large hard drives