Apple Performa 6400/180 - Manual (Page 43)

Basics Cache Expansion - 41
Cache Expansion
The optional 256K (512K for the 6500/275 and
6500/300) level-2 cache is on a 160-pin DIMM card that
plugs into a 160-pin edge connector on the logic board and
includes an integrated cache controller.
Note:
Apple does
not
support third-party cache cards for
these computer models. The 160-pin cache expansion slot is
not
compatible with cache cards for previously released
Power Macintosh computer models.