IFSHLP.SYS is an 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...

 device driver included with 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...

. It enables Windows to make direct file system calls bypassing MS-DOS methods and use native 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...

 for both local and network devices. IFSHLP first shipped with Windows for Workgroups 3.11 and was also used in Windows 9x

Windows 9x

Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced since 1995, which were based on the original and later modified Windows 95 kernel...

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The purpose of the IFS Helper is to ensure that no 3rd-party drivers intercept INT 21h

MS-DOS API

The MS-DOS API is an API used originally in MS-DOS/PC-DOS, and later by other DOS systems. Most calls to the DOS API invoke software interrupt 21h . By calling INT 21h with a subfunction number in the AH processor register and other parameters in other registers, one invokes various DOS services...

 calls; to achieve this, the IFSHLP.SYS is insured to be the first in the driver chain that intercepts DOS file access. If no other real-mode drivers are installed, IFSHLP will report that to the IFS Manager (IFSMGR.VXD in Windows 9x) and 32-bit file access will be enabled.

Inside the Windows 95 file system (ISBN 9781565922006) explores the 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...

 device driver kit and covers IFSHLP.SYS

IFSHLP.SYS

IFSHLP.SYS is an MS-DOS device driver included with Microsoft Windows. It enables Windows to make direct file system calls bypassing MS-DOS methods and use native 32-bit file access for both local and network devices...

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