32-bit Disk Access
Encyclopedia
32-bit Disk Access refers to a special disk access and caching mode available in older, MS-DOS
-based Microsoft Windows
operating systems. It was a set of protected mode
device driver
s that worked together to enhance the system's BIOS. It filtered interrupt 13h BIOS calls to the disk controller
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.
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.
32-bit disk access should not be confused with 32-bit file access
. Although both technologies are similar, 32-bit disk access was introduced with Windows 3.1 and file access with Windows for Workgroups 3.11. 32-bit file access provided a 32-bit code path for Windows to directly access the disk bus by intercepting the MS-DOS
Int 21H services while remaining in 386 protected mode
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.
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.
The Windows NT
family of operating systems including the newer Windows 2000
, Windows XP
, Windows Server 2003
, Windows Vista
and later always have 32-bit disk drivers active, cannot use MS-DOS drivers at all, and the expression is not used for them.
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
-based Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
operating systems. It was a set of protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
device driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s that worked together to enhance the system's BIOS. It filtered interrupt 13h BIOS calls to the disk controller
Disk controller
The disk controller is the circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card...
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.
Windows 3.1 had an option in its 386 Enhanced Control Panel
Control Panel (Windows)
The Control Panel is a part of the Microsoft Windows graphical user interface which allows users to view and manipulate basic system settings and controls via applets, such as adding hardware, adding and removing software, controlling user accounts, and changing accessibility options...
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
Virtual DOS machine
Virtual DOS machine is Microsoft's technology that allows running legacy DOS and 16-bit Windows programs on Intel 80386 or higher computers when there is already another operating system running and controlling the hardware.-Overview:...
would loop forever.
32-bit disk access should not be confused with 32-bit file access
32-bit File Access
32-bit file access refers to the higher performance, protected mode disk caching method introduced in Windows for Workgroups 3.11, which replaced SmartDrive . It bypassed MS-DOS and directly accessed the disk, either via the BIOS or 32-bit disk access...
. Although both technologies are similar, 32-bit disk access was introduced with Windows 3.1 and file access with Windows for Workgroups 3.11. 32-bit file access provided a 32-bit code path for Windows to directly access the disk bus by intercepting the MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
Int 21H services while remaining in 386 protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
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.
Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
, Windows 98
Windows 98
Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...
, and Windows Me
Windows Me
Windows Millennium Edition, or Windows Me , is a graphical operating system released on September 14, 2000 by Microsoft, and was the last operating system released in the Windows 9x series. Support for Windows Me ended on July 11, 2006....
use native, protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
32-bit disk drivers during normal operation. However Safe Mode
Safe Mode
Safe mode is a diagnostic mode of a computer operating system . It can also refer to a mode of operation by application software. Safe mode is intended to fix most, if not all problems within an operating system...
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.
The Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
family of operating systems including the newer Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
, Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
, Windows Server 2003
Windows Server 2003
Windows Server 2003 is a server operating system produced by Microsoft, introduced on 24 April 2003. An updated version, Windows Server 2003 R2, was released to manufacturing on 6 December 2005...
, Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
and later always have 32-bit disk drivers active, cannot use MS-DOS drivers at all, and the expression is not used for them.