IFSHLP.SYS (the Installable File System Helper) is a MS-DOS device driver that was first released as part of Microsoft Windows 3.11. It enables native 32-bit file access in Windows 386 Enhanced Mode by bypassing the 16-bit DOS API and ensuring that no other real mode driver intercepts INT 21h calls.
The protected mode counterpart of IFSHLP.SYS is IFSMGR.386 in Windows 3.11 and IFSMGR.VXD in Windows 95 and Windows 98.
Inside the Windows 95 file system (ISBN 9781565922006) explores the Windows 95 device driver kit and covers IFSHLP.SYS.
References
IFSHLP.SYS Wikipedia(Text) CC BY-SA