IBM Gets Deadly Serious
The conventional wisdom is that the battle for technical and performance leadership in the high end 64 bit microprocessor market will be a two way fight between future IA-64 and Alpha devices. With the recent disclosure of detailed information about the processor core of the POWER4 server MPU at Microprocessor Forum 2000, it appears IBM is preparing to leapfrog its way to preeminence in the 64 bit MPU market within the next 12 months. Pulling hard on every technological lever at its disposal, IBM has aggressively, and apparently successfully, pushed the envelope forward in many processor related engineering disciplines.
IBM has designed perhaps the most capable superscalar RISC core yet seen, and implemented the design in a state of the art 0.18 um SOI CMOS process utilizing 7 layers of copper interconnect. Not satisfied with that, IBM places not one but two processor cores on a huge 400 mm2 die with three independent, high bandwidth L2 caches, each approximately half a megabyte in capacity [1]. In addition, the POWER4 device integrates controller logic for external L3 cache and main memory, along with interprocessor communications channels for a total chip complexity of about 170 million transistors. To keep such a powerful and hungry processing complex fed, this chip includes very wide high speed buses which require about 5200 off-chip solder-ball pads, of which roughly 2200 are I/O signals, while the remainder provide power and ground connections.
The icing on the POWER4 cake is the packaging technology, which is shown below in Figure 1. Drawing heavily on IBM’s extensive experience over the last several decades in designing and manufacturing large and sophisticated multi-chip modules (MCMs) for its mainframes, four separate POWER4 dice are combined on a single ceramic MCM mounted in a rugged metal frame less than 5 inches on a side. This single unit, resembling a S/390 mainframe thermal conduction module (TCM), contains the core of a tightly coupled 8-way symmetric multiprocessor (SMP) server system.
Figure 1 POWER4 Packaging and Interconnection Hierarchy
The four POWER4 devices within the MCM are placed such that the two chip edges with the inter-chip communication drivers are facing inwards. This allows the four devices to create a network topology based on a fully connected graph with a minimal amount of substrate interconnect. Between any two POWER4 devices in the MCM there are separate unidirectional 128 bit wide links in each direction that transfer data at ½ the processor clock rate.
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