IBM Aptiva Hardware Handbook page 146

To reset the jumper, do the following:
1.
Locate the jumper you need to reset.
2.
Lift the jumper from Position 1 and move it to
Position 2, as shown in the picture.
Position 1
Jumper
Jumper
Pins
(0 or 256K)
3.
Reinstall all hardware you removed to access the
cache memory module sockets.
134 Installing cache memory
JP6
Position 2
(512K)