IBM HANDBOOK 260 - Manual (Page 88)

70 RS/6000 43P 7043 Models 150 and 260 Handbook
The processor subsystem is implemented on pluggable cards. Two processor
card slots are available. If two processor cards are installed in the system,
they must both be the same type or the system will not power on.
3.2.2.2 System Planar Board
One planar is installed in a Model 260. It provides the system bus and card
connections for the riser card, a voltage regulator, and clock module and four
memory DIMM slots. Power supply connections, I/O connections, and a
pin-grid array socket for the PowerPC processor.
One or two 200 MHz POWER3 processors can be installed.
Figure 23 shows the location of the I/O board components, Table 10 lists their
attributes.