Epson 486SX - Manual (Page 105)

A math coprocessor speeds up the numeric calculations and
graphic displays your computer performs when using certain
application software. The 50 MHz model includes a built-in
math coprocessor. If you have the 25 MHz model and you want
math coprocessor capabilities, you must remove your 80486SX
microprocessor and install the 80487SX microprocessor (with
an internal math coprocessor). Because the system circuitry
may be damaged if this procedure is not performed correctly,
you must have an authorized Epson dealer or Service Center do
it for you.
This chapter also explains how to change the jumper settings
inside the computer. You need to change jumper settings if you
add memory modules, install certain types of option cards, or
want to change the way your computer operates.
In addition, you’ll find an illustration of your main system
board which shows the location of the jumpers, option slots,
and any other components you may need to locate.
Before you can change jumper settings or install any of the
options mentioned above, you need to remove the cover from
the computer. See Chapter 5 for instructions.
6-2 Installing and Removing Options