NEC POWERMATE PROFESSIONAL 9000 Service Manual page 169

If you are installing two processors, the following values must be identical for both
processors:
T
second-level cache size and type (ECC or non-ECC)
T
operating voltages
T
maximum bus and core frequencies.
Both processors must be of the same stepping or 1 step different (such as C0 to C1).
These values can be determined by checking the parameters of the "s-spec" number. The
"s-spec" number is a five-character code (for example, SL28R) printed on the top edge of
the SEC.
When upgrading the processor, use the BIOS Setup utility Maintenance Menu Configure
mode to change the processor speed (if necessary).
CAUTION: In a single processor configuration,
the processor must be installed in the boot
processor Slot 1 connector (the slot closest to
the back panel) and a termination card must be
installed in the application processor slot. If the
processor is installed in the second Slot 1
connector (the application processor slot), the
computer will not boot.
CAUTION: If the operating voltages do not
match, the computer will not boot.
NOTE: When the system is jumpered for
Configure mode and restarted, the processor
speed always returns to the default setting of
233-MHz. If the processor runs at a speed other
than 233-MHz, the speed must be reset in the
BIOS Setup utility Maintenance Menu when the
system is brought up in Configure mode.
Option Installation 3-15