PA-7200
PA-RISC microprocessor for small multiprocessor systems, derived from PA-7100.
The PA-7200, also called the PCX-T and code-named Thunderbird, is a microprocessor built by Hewlett-Packard (HP) that runs the PA-RISC 1.1 instruction set architecture. It launched in early 1995, first appearing in HP systems. HP developed it for small multiprocessing setups using two or four processors. HP did not sell the chip openly; the only outside companies to use it were Convex Computer and Stratus Computer, both members of the Precision RISC Organization (PRO). The microprocessor was first presented at the Compcon and IEEE International Solid-State Circuits Conference (ISSCC).
The PA-7200 was largely based on the PA-7100, with the main improvement being the addition of a second integer unit. This allowed the chip to issue up to two integer instructions per cycle. The second unit was not identical to the first and could only handle simple but commonly used instructions.
The chip contained 1.3 million transistors and measured 14.0 mm by 15.0 mm (210 mm²). HP manufactured it using the CMOS14A process, which HP co-developed with Analog Devices. CMOS14A was a 0.55 μm, three-level interconnect, complementary metal–oxide–semiconductor (CMOS) process.
The PA-7200 uses an unusual 4.4 V power supply, a result of its development history. It was originally designed for the 0.8 μm CMOS26B process, reusing circuits and layouts from the PA-7100, which was also built for CMOS26B. The completed design was then shrunk for the 0.55 μm CMOS14A process. That process had a 120-angstrom gate oxide that could not tolerate 5.0 V operation. A 3.3 V supply, however, did not allow the chip to reach its target clock frequency, so 4.4 V was chosen as a compromise.
- Introduced
- early 1995
- Isa
- PA-RISC 1.1
- Developer
- Hewlett-Packard (HP)
- Transistors
- 1.3 million
- Die size
- 14.0 mm by 15.0 mm (210 mm²)
- Fabrication process
- CMOS14A (0.55 μm, three-level interconnect)
- Power supply
- 4.4 V
Lore & Background
The PA-7200 was mostly derived from the PA-7100 and improved by adding a second integer unit, enabling it to issue up to two integer instructions per cycle. The second integer unit was not identical to the first and was only capable of executing simple but more frequently used instructions. The microprocessor contained 1.3 million transistors and measured 14.0 mm by 15.0 mm (210 mm²). It was fabricated by Hewlett-Packard in their CMOS14A process, co-developed with Analog Devices, a 0.55 μm, three-level interconnect CMOS process.
The microprocessor uses an unusual 4.4 V power supply as a result of its development. It was designed in the 0.8 μm CMOS26B process and leveraged circuits and layouts from the PA-7100, which was also designed for CMOS26B. The completed design was then shrunk for the 0.55 μm CMOS14A process. This process has 120-angstrom gate oxide that did not tolerate 5.0 V operation. A 3.3 V power supply did not enable the microprocessor to achieve the intended clock frequency, so 4.4 V was chosen as a compromise.
The PA-7200 was first described at the Compcon and IEEE International Solid-State Circuits Conference (ISSCC) conferences. It was developed for small multiprocessing systems with two or four microprocessors.
Reader's Guide
The PA-7200 represents a transitional design in Hewlett-Packard's PA-RISC line, bridging the PA-7100 and later processors by adding a second, simpler integer unit to improve instruction throughput without a full redesign. Its development path—starting from the 0.8 μm CMOS26B process and then shrinking to the 0.55 μm CMOS14A process—illustrates the engineering compromises required when migrating to a new fabrication technology. The 4.4 V power supply, chosen as a compromise between the incompatible 5.0 V and the insufficient 3.3 V, highlights the constraints of the 120-angstrom gate oxide in the CMOS14A process. The microprocessor's limited third-party adoption, restricted to Convex Computer and Stratus Computer through the Precision RISC Organization, underscores HP's strategy of keeping the design primarily for internal systems. Its focus on small multiprocessor configurations (two or four CPUs) positioned it for cost-effective multiprocessing in HP's server and workstation lines, though it was never sold openly on the merchant market.
Did You Know?
- The PA-7200 was also known as PCX-T and code-named Thunderbird.
- It was fabricated in a 0.55 μm CMOS14A process co-developed by Hewlett-Packard and Analog Devices.
- The microprocessor uses an unusual 4.4 V power supply as a compromise between 5.0 V and 3.3 V.
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