How to Simulate INT 15 Rather Than Calling EISA BIOS Directly

• Microsoft Windows 95

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, you should first make a backup copy of the registry files (System.dat and User.dat). Both are hidden files in the Windows folder.

SYMPTOMS

You computer stops responding (hangs) during the boot process.

CAUSE

Some programs (such as QEMM Stealth and EMM386.EXE with the /HIGHSCAN switch) map over part of the BIOS. If RAM has been mapped over the EISA BIOS, your computer may hang when Windows calls the BIOS.

Windows 95 calls an EISA BIOS in one of two ways:

• Using INT 15.
• With a direct call to a published entry point.

RESOLUTION

Windows 95 attempts to detect cases of RAM mapping so that it can change the way it calls the EISA BIOS. For example, if Windows 95 detects QEMM Stealth it calls the BIOS by simulating INT 15. To do this, Windows adds an EISASimulateInt15 entry to the registry and gives the entry a value of 01. The default value, 00, means that Windows communicates with the EISA BIOS directly.

If you suspect that your computer is hanging because of the way Windows is accessing the BIOS, add EISASimulateInt15 to

   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\System

NOTE: For information about how to edit the registry, view the Changing Keys And Values online Help topic in Registry Editor (Regedit.exe). Note that you should make a backup copy of the registry files (System.dat and User.dat) before you edit the registry.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall Windows 95. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.