Epson 3865X Plus - Manual (Page 14)

You may also want to install an 80387SX, 16 MHz math
coprocessor in your computer to speed up mathematical
calculations in certain application programs. Check with your
authorized Epson dealer to see which options are available.
Operating Systems and Other Software
You probably have a version of MS-DOS: the operating system
by Microsoft? to use with your Equity 386SX PLUS. Epson has
enhanced MS-DOS by adding two time-saving utilities-HELP
and MENU-that make it easier to use. The HELP program lets
you display information on the screen about any MS-DOS
command. MENU provides an easy way to run many useful
MS-DOS commands.
Version 4.01 of MS-DOS also includes the Shell program,
which lets you run MS-DOS commands by selecting options
from on-screen menus. MS-DOS version 3.3 comes with the
XTREE® program. XTREE allows you to use on-screen menus
to perform a wide variety of file and directory operations.
You probably also purchased other software; you can use
virtually any application program designed for the IBM PC,
PC XT, PC AT, or compatible computers on your Equity 386SX
PLUS. You may also use powerful 32-bit software-such as
Microsoft Windows/386™-with your computer.