The PowerPC 603 microprocessor. (The Making of the PowerPC) (Cover Story)

In October 1993, Motorola and IBM unveiled the first low-power version of the PowerPC family--the PowerPC 603 microprocessor. Measuring a mere [85mm.sup.2] (7.4 x 11.5 mm) in size, the 603 contains 1.6 million transistors and consumes less than 3 watts of power when operating at 80MHz. With estimated performance values of 75 SPECInt92 and 85 SPECfp92, the 603 is comparable in performance to present-day high-end personal computer and workstation processors. This member of the PowerPC family is designed to bring high-performance and low-power capabilities to the laptop and low-cost desktop computer markets.

Following closely on the heels of its predecessor, the PowerPC 601 microprocessor [1], the 603 microprocessor was developed at the joint Motorola/IBM/Apple Somerset Design Center in Austin, Texas. The 603 microarchitecture evolved from Apple, IBM, and Motorola's collective experience on several past designs. The similarity of the POWER and PowerPC architectures permitted the use of sample traces generated by RISC System/6000 machines for evaluation of design trade-offs. The compiler groups also provided their insight to ensure the traces from the past generation of processors and compilers, with their own specific peculiarities, did not misguide the 603's microarchitecture definition, and that tradeoffs selected were appropriate for the next generation of compilers.

To accelerate the design and test process, engineers employed a formal VLSI design methodology derived from the best of both IBM and Motorola's CAD tools. These tools enable both the rapid design and dense packing capability necessary to produce very high-volume, high-yield microprocessors for the commercial market. The 603 design team employed a combination of custom circuitry (for arrays), library components (for data paths), and standard cell place and route (for random logic) to accomplish the 603 design.

Using the best tools and methodology available, the design team took the 603 from concept to working silicon in 18 months. Ongoing design evaluation and debugging, including simulation of 28 billion processor cycles prior to tape-out, provided fully functional first-pass silicon that ran at the design target speed of 80MHz.

The PowerPC 603 microprocessor is manufactured by Motorola in Austin, Texas, and by IBM in Burlington, Vt. Motorola and IBM both fabricate the 603 using a 0.5[micro]m, 4-level metal, 3.3VDC CMOS process with design rules compatible with both companies' semiconductor processes. The die is designed to be packaged in either a 240-pin ceramic quad flat pack or a ball-grid array package. Figure 1 is a photograph of the 603 die.

Functional Overview

The 603 is the first processor in the PowerPC family to fully support the PowerPC Architecture. It incorporates five execution units: branch, integer, floating-point, load/store, and system register; and a pair of on-chip 8KB instruction and data caches.

Since the 603 is a super-scalar micro-processor, it is capable of issuing and retiring as many as three instructions per clock to these execution units. For increased performance, the 603 allows instructions to be executed out-of-order. Additionally, the 603 provides programmable power reduction modes that permit systems designers the flexibility of implementing a variety of power management techniques. A block diagram of the 603 is shown in Figure 2.

Instructions are dispatched inorder to one of the five execution units. If there are no operand …