Microsoft 32-bit disk access

32-bit Disk Access (also known as FastDisk) refers to a special disk access and caching mode available in older, <a href="/facts/MS-DOS/fVrrz1uN">MS-DOS</a>-based <a href="/facts/Microsoft_Windows/bwhAhuSL">Microsoft Windows</a> operating systems. It was a set of <a href="/facts/Protected_mode/y5u3Gwqq">protected mode</a> <a href="/facts/Device_driver/rDYnHU1G">device drivers</a> that worked together to take advantage of advanced disk I/O features in the system BIOS. It filtered <a href="/facts/INT_13H/01oMYPbW">interrupt 13h</a> <a href="/facts/BIOS_call/UThr5YWN">BIOS calls</a> to the <a href="/facts/Disk_controller/dfRSYlMq">disk controller</a> and directed them in the most efficient way for the system — either through the 32-bit interface with the hard disk controller or through the system BIOS. Using 32-bit Disk Access allowed for more pageable memory in Windows to page MS-DOS–based applications to disk to free enough RAM for applications when they needed to use it. Sometimes enabling this mode would break older applications of the day.
<a href="/facts/Windows_3.1/zYnWyaC6">Windows 3.1</a> had an option in its 386 Enhanced <a href="/facts/Control_Panel_(Windows)/WEfhKClH">Control Panel</a> 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 <a href="/facts/Virtual_DOS_machine/Wv1jNzBx">virtual DOS machine</a> would loop forever.
32-bit disk access should not be confused with <a href="/facts/32-bit_file_access/IWMRF5HS">32-bit file access</a>. Although both technologies are similar, 32-bit disk access was introduced with Windows 3.1 and file access with <a href="/facts/Windows_for_Workgroups/zYnWyaC6">Windows for Workgroups</a> 3.11. 32-bit file access provided a 32-bit code path for Windows to directly access the disk bus by intercepting the <a href="/facts/MS-DOS/fVrrz1uN">MS-DOS</a> Int 21H services while remaining in 386 <a href="/facts/Protected_mode/y5u3Gwqq">protected mode</a> and at CPU speeds, rather than handling the Int 21H services in real mode by MS-DOS. 32-bit disk access offers less performance and is less likely to work on many computers than 32-bit file access. 32-bit file access does not require 32-bit disk access.
<a href="/facts/Windows_95/1E1L93qC">Windows 95</a>, <a href="/facts/Windows_98/6qtq4oJm">Windows 98</a>, and <a href="/facts/Windows_Me/fjENFRNa">Windows Me</a> use native, <a href="/facts/Protected_mode/y5u3Gwqq">protected mode</a> 32-bit disk drivers during normal operation. However <a href="/facts/Safe_Mode/k4BJ7AGP">Safe Mode</a> 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.
32-bit versions of the <a href="/facts/Windows_NT/EtccWvxQ">Windows NT</a> family of operating systems including the newer <a href="/facts/Windows_2000/amJIt9gz">Windows 2000</a>, <a href="/facts/Windows_XP/IozrkAYS">Windows XP</a>, <a href="/facts/Windows_Server_2003/3vIJam5L">Windows Server 2003</a>, <a href="/facts/Windows_Vista/IASEUCTB">Windows Vista</a> and later always have 32-bit disk drivers active, cannot use MS-DOS drivers at all, and the expression is not used for them.

<ul><li><a href="https://web.archive.org/web/20110926214952/http://support.microsoft.com/?id=83325">Explanation of SMARTDRV & 32-bit disk access from Microsoft</a></li>
<li><a href="https://web.archive.org/web/20110926215051/http://www.knowplace.org/pages/morgue/windows_9.x3.1_32-bit_guide.php">32-bit in Windows 3.1 / 9x</a></li>
<li><a href="https://web.archive.org/web/20070324064925/http://pclt.cis.yale.edu/pclt/OPSYS/WFWG311.HTM">https://web.archive.org/web/20070324064925/http://pclt.cis.yale.edu/pclt/OPSYS/WFWG311.HTM</a></li></ul>

Microsoft 32-bit disk access open-in-new

Microsoft 32-bit disk access