Enterprise X000 systems are tested for operation in ambient temperatures
ranging from 0 to 40 degrees Centigrade (32 to 104 degrees Fahrenheit).  
Each CPU/Memory module has a thermistor installed below each of the processor 
boards.  The analog output from each thermistor is fed to an analog-to-digital 
converter and the resulting value is placed in a system register for reading 
by software.

The same implementation is used on the I/O Boards and the Clock Board, so
accurate temperature readings are maintained for all core system boards.  The
sampled temperature is used to drive the speed of the cooling fans enclosed in
the 300 watt PCMs.  It is possible to have different PCMs running fans at
different speeds to provide sufficient cooling for a particular area of the
system.

Note that a memory-only CPU/Memory Board will not provide any temperature data,
as no thermistors are installed for monitoring memory SIMM temperatures.  This
does not adversely effect system reliability in any way, since memory SIMMs do
not generate a significant amount of heat.

Software control is performed via a polling mechanism implemented in Solaris,
which reads the temperature registers every 2 seconds.  If the temperature
reaches a "yellow zone" threshold, the system will emit warnings via
console messages.  If the temperature hits a "red zone" threshold, the system
will continue and repeat the warning.  Should the affected component stay in 
the red zone for 20 seconds or longer, the system will either power the 
component down or power itself down entirely, depending on the implementation 
level of the product.

Monitoring software sets the "yellow zone" at 73 to 82 degrees Celsius
for CPU/Memory Boards and 60 to 67 degrees Celcius for I/O Boards and the 
Clock Board.  The "red zone" is set to temperatures at 83 degrees Celsius
on CPU/Memory Boards and temperatures at 68 degrees Celsius for I/O Boards 
and the Clock Board.

Board Type	Yellow Temps		Red Temps
--------------------------------------------------

CPU		73C - 82C		83C - up
I/O		60C - 67C		68C - up
CLOCK		60C - 67C		68C - up


                  

About hot swap:

At initial availability of Enterprise X000 server systems, the ability to
dynamically take core system components out of service without a reboot (hot
swap) was not available.  Therefore, an over temperature condition would result
in an entire system power down.  Over time, Sun has extended its hot swap
capabilities, and the system (if these capabilities are incorporated) will be
able to dynamically configure out core system components such as CPU/Memory
Boards and I/O Boards so they can be individually powered down without shutting
down Solaris. Solaris 2.6 HW 5/98 is required to support I/O boards.  I/O
boards are the only supported boards at this time.