Service manual

1-4 AlphaServer GS160/320 CPU Addition and Removal

Table 1–4 Comparison of System Boxes

System Box

Part Number

Cache Size

Supported

by the Box Comments

BA51A-AA

(54-25043-01/02)

4Mbytes

Though the B4166 CPU has an 8-Mbyte B-cache, only

4 Mbytes are used when placed in this backplane.

BA51A-BA

(54-25045-01/02)

4 or 8 Mbytes When all CPUs in this backplane are B4166, all use 8

Mbytes of B-cache. If CPUs are mixed, B4125 and

B4166 on the same backplane, all are configured for

the 4-Mbyte B-cache size.

In summary:

• The BA51A-AA and BA51A-BA system boxes can coexist in a system.

• The B4125 CPUs run at 731 MHz and require a 9.6 ns system clock. B4125

CPUs are not supported with the 9.0 ns system clock.

• B4125 CPUs have 4 Mbytes of B-cache. When in a QBB in a BA51A-BA

system box, firmware configures these CPUs to be consistent with the

amount of B-cache available.

• The B4166 CPU can operate at different speeds and use different amounts

of its B-cache depending upon the system box it is in, the system clock

speed, and whether it is configured with the B4125 CPU or not.

• The B4166 CPU requires that the SRM console firmware be at V6.0 or

higher and that the microprocessor firmware be at V6.0 or higher.

Are there additional restrictions when adding or changing CPUs

when the operating system is running?

Yes, because the firmware recorded what speed modules were in which slots at

system startup, you should not change the speed of the CPU in that slot. The

firmware will not take note of the change in the CPU until the next power cycle.*

Terminology clarification

Power cycle: Occurs when the SRM or SCM power off console command is issued, followed by the SRM

power on command. Power is turned off and on, testing begins, and the SRM prompt returns.

Initialize: Occurs when the SRM initialize command is issued; it causes the I/O adapters to initialize. The

system must then be booted.

Reboot: Occurs at the operating system level; causes an SRM initialize command.

Reset: Occurs when the control panel Reset button is pushed or when the SRM or SCM reset command i

issued. This causes a system-level hardware reset, initiating testing and return of the SRM

prompt. Power is not turned off.