Processor Module

The processor module is a separate logic board that contains one or two G4 microprocessors and their external memory caches (if any).

The processor module is connected to the main logic board by way of a 300-pin connector. To achieve the required level of performance, the signal lines that connect the processor module and the main logic board are carefully matched in length, loading, and impedance.

WARNING

DON’T TRY TO USE OLDER PROCESSOR CARDS! This connector differs from those in earlier G4 computers and it is not pin-compatible.

This section covers:

PowerPC G4 Microprocessor
Cache Memory
Dual Processors

PowerPC G4 Microprocessor

The PowerPC G4 microprocessor used in the Xserve computer has many powerful features, including a pipelined system bus, called MaxBus, that is more efficient than the system bus on the PowerPC G3 microprocessors.

The PowerPC G4 used in the Xserve computer has the following features:

• 32-bit PowerPC implementation


• superscalar PowerPC core


• Velocity Engine (AltiVec technology): 128-bit-wide vector execution unit


• high bandwidth MaxBus


• fully symmetric multiprocessing capability


• dual 32 KB instruction and data caches (level one)


• built-in 256 KB backside L2 cache per processor


• support for up to 2 MB backside L3 cache per processor


• on-chip L3 tag storage

To find more information, see the reference at “PowerPC G4 Microprocessor”.

Cache Memory

In addition to the 256 KB L2 per processor cache built into the PowerPC G4 microprocessor, the processor card also has an external level 3 (L3) backside cache. The L3 cache consists of 2 MB of high-speed SRAM runing at a clock speed of 223 MHz (6:1 ratio).

Note: The Xserve computer does not use jumpers to control the clock speeds of the processor and cache.

Dual Processors

The dual-processor configuration of the Xserve computer has a processor card that contains two PowerPC G4 processors, each with its own external L3 cache. The dual-processor configuration allows applications that support multitasking to about double their performance.

Note: The cluster node Xserve computer is available only in dual configuration.