Epson EL 3S/33 - Manual (Page 39)

Some copy-protected programs require the computer to run at
low speed while accessing the program on a diskette. These
programs also usually require you to leave a key disk-the
diskette that contains the copy protection-in the diskette
drive. If you use a copy-protected program, you can change the
speed to low to access the diskette and return it to high speed
when you are finished.
You can change the processor speed temporarily by entering
one of the following commands from the numeric keypad on
your keyboard:
To select low speed, press Ctrl Alt -. (Hold down the Ctrl
key and the Alt key simultaneously and then press the - key
on the numeric keypad.) The speed light turns off.
To select high speed, hold down the Ctrl and Alt keys and
press + on the numeric keypad. The speed light comes on.
Note
You can use the commands listed above while you are
running a program. However, if the program uses one of
these commands for another function, you cannot use it to
change the processor speed. You can, however, change the
processor speed through the SETUP program.
The speed setting remains in effect until you do the following:
Reset your computer
Turn off your computer
Change the speed with another keyboard command
Change the speed setting in the SETUP program.
Using Your Computer 2 - 7