Using Weitek Math Coprocessor with MS-DOS (72595)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22

This article was previously published under Q72595


The default setting in EMM386.EXE for the Weitek coprocessor is Off. If the switch for the Weitek coprocessor is not set to On when EMM386.EXE is loaded and the machine contains a Weitek coprocessor board, the machine may stop responding (hang) on boot.

MS-DOS must be loaded low if the W=ON switch is specified for EMM386.EXE. If Weitek support is enabled, EMM386 will attempt to allocate the high memory area (HMA) and map the memory locations used by the Weitek coprocessor to this location. If MS-DOS is already loaded high, this will not be possible.

NOTE: Weitek can be used in conjunction with the 80387 math coprocessor, although special code must be written to use each device.


The WTL 1167 is a set of three chips found on the Weitek coprocessor board that are used as a replacement for the Intel 80387. To use EMM386.EXE on a machine with the Weitek coprocessor installed:

    Add EMM386.EXE to the CONFIG.SYS file as follows:
          device=c:\dos\emm386.exe w=on
    This example assumes that EMM386.EXE is located in the C:\DOS directory.
    If the EMM386 device driver has been loaded in CONFIG.SYS, you can toggle Weitek coprocessor support on and off by typing the following at the DOS prompt:

    emm386 w=on


    emm386 w=off

The following machines may be shipped with the Weitek coprocessor board installed:

Compaq Deskpro 386/20e, Model 110
HP Vectra RS/16 PC
HP Vectra RS/20 PC

Modification Type: Major Last Reviewed: 5/10/2003
Keywords: KB72595