Dec 092017
Latest version of 80x87 simulator for 286 and 386 machines. Slow, but needed to run some 80x87 specific software (such as AUTOCAD) if no 80x87 chip is present.
File EM87V1_4.ZIP from The Programmer’s Corner in
Category Utilities for DOS and Windows Machines
Latest version of 80×87 simulator for 286 and 386 machines. Slow, but needed to run some 80×87 specific software (such as AUTOCAD) if no 80×87 chip is present.
File Name File Size Zip Size Zip Type
EM87.DOC 6056 2449 deflated
EM87.EXE 17513 10471 deflated
EM87.SYS 541 444 deflated

Download File EM87V1_4.ZIP Here

Contents of the EM87.DOC file

EM87 V1.46/9/90

This program fully emulates the 8087 math coprocessor on 80286
and 80386 based computers. This is useful to run software that requires
the 8087/80287/80287. This program does not emulate the 80287/80387
extensions to the 8087 instruction set, but most software I have seen
only uses the 8087 instructions to be PC/XT compatible. Please note that
floating point emulation is MUCH slower than the real thing (but also
much cheaper!).
Unfortunately, this method of emulation does not work on the 8088
and 8086 based computers because these processors do not have emulation
support built in.


Version 1.1 fixes problems with programs that access extended memory,
will not load if a real 80X87 is present.

Version 1.2 fixes problems uninstalling EM87 under certain versions of
DOS. Also display of the help screen would lock up some machines.

Version 1.3 allows floating point exception interrupts to properly
cause a non-maskable interrupt when enabled. Very few programs use this feature.
The lack of this capability caused programs that needed it to do strange things
to the video display.

Version 1.4 will not attempt to load on a 8088/8086/V20 processor
machine. Note that the program has been changed from a .COM to a .EXE file. You
must delete the old program. Copying the new program will not overwrite the old
one! EM87 is now compatible with 80386 memory managers, see section below.

If you are using a 80386 memory manager:
To load EM87 on an 80386 machine with a memory manager loaded (such as
QEMM, 386MAX, EMM386.SYS) you MUST place the device driver, EM87.SYS, in your
CONFIG.SYS by putting the line:
as the FIRST line in your CONFIG.SYS. This line MUST be before the line that
installs the memory manager! You must also place the line:
EM87 /L
in your AUTOEXEC.BAT. If EM87.EXE is not loaded after EM87.SYS and before ANY
program that checks for or uses the numerics coprocessor, your system WILL
crash! EM87 can not be unloaded if you are using a 80386 memory manager. It can
be loaded into high memory if your memory manager has the capability to load
programs in high memory. Do not load EM87.SYS into high memory, as it does not
remain resident anyways.

Do NOT use EM87.SYS if you are not running a 80386 memory manager!

Tested with:

AUTOCAD release 9.
AUTOCAD release 10.
Microway's 87TEST v1.20 (A very intensive 8087 test program).
FATMAN30 (A great mandelbrot generator!).
NORTON UTILITIES 4.5 SI (Reports a 8087 present).

Does not work with:

Possibly any other program that uses a DOS extender (286 or 386
protected mode).
Probably only works with WINDOWS 3.0 in real mode.

EM87>Display the help screen.
EM87 /L>Load the emulator.
EM87 /U>Unload the emulator.

EM87 returns the error codes as shown in the section below to MSDOS.

Possible messages:

========EM87.SYS always displays the lines:

EM87.SYS V1.4 preload driver for 386 memory managers.
Copyright (C) 1990 by Ron Kimball. All rights reserved.

========followed by one of the following lines:

EM87.SYS successful. Thanks for using EM87!

Extended memory manager loaded! EM87.SYS must be loaded first! Can't load!

Math coprocessor detected! Can't load!

Not an 80386! Can't load!

========EM87.EXE always displays the lines:

EM87: 8087 emulator for 80286 and 80386 based computers.
Version 1.4 (c) 1989, 1990 by Ron Kimball. All rights reserved.
If you continue to use this program after evaluation
you must send 5 dollars for registration to:
RR01 BOX 15Y

========followed by one of the following messages: ERROR CODE
========Command line = EM87 ==========

Usage: EM87 /L Installs the emulator. 1
EM87 /U Removes the emulator from memory.

========Command line = EM87 /L

8087 emulator loaded. Thanks for using EM87! 0

Math coprocessor detected! Can't load! 2

Processor must be 80286 or 80386! Can't load! 4

Extended memory manager loaded! EM87.SYS must be loaded first! Can't load! 5

EM87 already loaded! Can't load! 7

========Command line = EM87 /U

EM87 unloaded. Thanks for using EM87! 0

EM87 was not resident! Can't unload! 3

Extended memory manager loaded! Can't unload! 6

Source code or custom version:
These are available with a license to use or distribute EM87 with your
software products. The price is usually $500.00 (Unless you need something
really unusual). Write with your needs!


This program may be freely distributed by anyone in its unmodified form
only and must be with this unmodified documentation file.

EM87 is copyright 1989, 1990 Ron Kimball, all rights reserved. It is
not "Public Domain" or "Freeware". If you intend to use this program after
evaluation you must send me five dollars for registration. Registration
entitles you to use EM87 on a single machine at any one time, and the right to
use (under the same terms) any future version of EM87 that may be released for
no further charge. Include the version number of EM87 that you are presently
using. Also please tell me of any new uses you may find for this program.
This registration may be transferred to another by merely notifying me
at the address below.
I will notify you of updates, which you may download from various
BBS's or obtain directly from me for a small charge. Thanks.

Ron Kimball
RR01 Box 15Y
Brookfield, Ma 01506

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