E4500 - Can't Get 100MHz Bus

It took me some time, so very long ago, to eventually understand this issue.

The system bus speed in Sun's Enterprise server systems, (E3000 through the E6500)

is a result of the configuration, not an elementary root function of the configuration.

It's the reverse of what you usually see in the PC universe.

Think of it as backwards to what you might have otherwise expected.

The clockboard governs what will be the proper bus speed, per the cpu's you've installed.

For your current configuration, you have 336MHz processors,

which have an inherent design multiplier/divisor of 4:1.

So ... 336 divided by 4 == 84

If you replaced those cpus with 400MHz modules,

and use FRUs that were designed for the same 4:1 divisor,

your E4500 gigaplane bus would spontaneously be clocked at 100MHz.

There's another "gotcha" for the E6000's and E6500's.

Since their centerplane is so very big, as perceived at a computer bit-and-byte level,

their system bus speed will NEVER be 100MHz.

There isn't enough power to drive them that fast and maintain data integrity.

The E6x00 clockboards will commonly set their bus to 80MHz to avoid EMI data corruption.

(5:1 and 6:1 divisors as may be appropriate)

rukbat at 2007-7-7 0:03:05 >

All eight of your current cpu modules are 336MHz and each has a 4mb L2 cache.

Your clockboard has set the gigaplane bus to 84MHz

because the cpus were designed and manufactured with a 4:1 divisor.

The clockboard is functioning perfectly.

Think of it as quickly peeking at the processors during POST, finding their clock ratio,

and then it sets the bus speed to whatever is best.

If you were to shut the system down and take one of those cpus out and examine it,

you would see that it has a part number of 501-4363.

That happens to be the only [url=http://www.sunshack.org/data/sh/2.1/infoserver.central/data/syshbk/Systems /E4500/component.cpu-module.html]336MHz part[/url] that's ever been in those systems.

A 100MHz bus speed is a theoretical maximum.

It will be that or slower.

You cannot set the bus speed. It will be, whatever it ends up as ...

rukbat at 2007-7-7 0:03:05 >