The arrival of this chip changed the course of chip development!
In the late 1970s, 8-bit processors were still the most advanced technology at the time, and CMOS processes were at a disadvantage in the semiconductor field. Engineers at AT&T Bell Labs took a bold step into the future, combining cutting-edge 3.5-micron CMOS manufacturing processes with innovative 32-bit processor architectures in an effort to outperform competitors in chip performance, surpassing IBM and Intel.
Although their invention, the Bellmac-32 microprocessor, failed to achieve the commercial success of earlier products such as the Intel 4004 (released in 1971), its influence was profound. Today, the chips in nearly all smartphones, laptops, and tablets rely on the complementary metal-oxide semiconductor (CMOS) principles pioneered by the Bellmac-32.
The 1980s were approaching, and AT&T was trying to transform itself. For decades, the telecommunications giant nicknamed "Mother Bell" had dominated the voice communications business in the United States, and its subsidiary Western Electric produced almost all the common telephones in American homes and offices. The U.S. federal government urged the breakup of AT&T's business on antitrust grounds, but AT&T saw an opportunity to enter the computer field.
With computer companies already well established in the market, AT&T found it difficult to catch up; its strategy was to leapfrog, and the Bellmac-32 was its springboard.
The Bellmac-32 chip family has been honored with an IEEE Milestone Award. Unveiling ceremonies will be held this year at Nokia Bell Labs campus in Murray Hill, New Jersey, and at the Computer History Museum in Mountain View, California.
UNIQUE CHIP
Rather than follow the industry standard of 8-bit chips, AT&T executives challenged Bell Labs engineers to develop a revolutionary product: the first commercial microprocessor capable of transferring 32 bits of data in a single clock cycle. This required not only a new chip but also a new architecture—one that could handle telecommunications switching and serve as the backbone of future computing systems.
"We're not just building a faster chip," said Michael Condry, who leads the architecture group at Bell Labs' Holmdel, New Jersey, facility. "We're trying to design a chip that can support both voice and compute."
At the time, CMOS technology was seen as a promising but risky alternative to NMOS and PMOS designs. NMOS chips relied entirely on N-type transistors, which were fast but power-hungry, while PMOS chips relied on the movement of positively charged holes, which was too slow. CMOS used a hybrid design that increased speed while saving power. The advantages of CMOS were so compelling that the industry soon realized that even if it required twice as many transistors (NMOS and PMOS for each gate), it was worth it.
With the rapid development of semiconductor technology described by Moore's Law, the cost of doubling transistor density became manageable and eventually negligible. However, when Bell Labs embarked on this high-risk gamble, large-scale CMOS manufacturing technology was unproven and the cost was relatively high.
This did not scare Bell Labs. The company drew on the expertise of its campuses in Holmdel, Murray Hill, and Naperville, Illinois, and assembled a "dream team" of semiconductor engineers. The team included Condrey, Steve Conn, a rising star in chip design, Victor Huang, another microprocessor designer, and dozens of employees from AT&T Bell Labs. They began to master a new CMOS process in 1978 and build a 32-bit microprocessor from scratch.
Start with design architecture
Condrey was a former IEEE Fellow and later served as Intel's Chief Technology Officer. The architecture team he led was committed to building a system that natively supported the Unix operating system and the C language. At the time, both Unix and the C language were still in their infancy, but were destined to dominate. In order to break through the extremely valuable memory limit of kilobytes (KB) at the time, they introduced a complex instruction set that required fewer execution steps and could complete tasks within one clock cycle.
Engineers also designed chips that support the VersaModule Eurocard (VME) parallel bus, which enables distributed computing and allows multiple nodes to process data in parallel. VME-compatible chips also enable them to be used for real-time control.
The team wrote its own version of Unix and gave it real-time capabilities to ensure compatibility with industrial automation and similar applications. Bell Labs engineers also invented domino logic, which increased processing speed by reducing delays in complex logic gates.
Additional test and verification techniques were developed and introduced with the Bellmac-32 module, a complex multi-chip verification and test project led by Jen-Hsun Huang that achieved zero or near-zero defects in complex chip manufacturing. This was a first in the world of very large scale integrated circuit (VLSI) test. Bell Labs engineers developed a systematic plan, repeatedly checked their colleagues’ work, and ultimately achieved seamless collaboration across multiple chip families, culminating in a complete microcomputer system.
Next comes the most challenging part: the actual manufacturing of the chip.
“At the time, layout, test, and high-yield manufacturing technologies were very scarce,” recalls Kang, who later became president of the Korea Advanced Institute of Science and Technology (KAIST) and a fellow of the IEEE. He notes that the lack of CAD tools for full-chip verification forced the team to print out oversized Calcomp drawings. These schematics show how transistors, wires, and interconnects should be arranged within a chip to give the desired output. The team assembled them on the floor with tape, forming a giant square drawing more than 6 meters on a side. Kang and his colleagues hand-drew each circuit in colored pencils, looking for broken connections and overlapping or improperly handled interconnects.
Once the physical design was complete, the team faced another challenge: manufacturing. The chips were produced at the Western Electric plant in Allentown, Pennsylvania, but Kang recalls that the yield rate (the percentage of chips on the wafer that met performance and quality standards) was very low.
To address this, Kang and his colleagues drove to the plant from New Jersey every day, rolled up their sleeves and did whatever was necessary, including sweeping floors and calibrating test equipment, to build camaraderie and convince everyone that the most complex product the plant had ever attempted to produce could indeed be made there.
“The team-building process went smoothly,” Kang said. “After a few months, Western Electric was able to produce high-quality chips in quantities that exceeded demand.”
The first version of the Bellmac-32 was released in 1980, but it failed to live up to expectations. Its performance target frequency was only 2 MHz, not 4 MHz. The engineers discovered that the state-of-the-art Takeda Riken test equipment they were using at the time was flawed, with transmission line effects between the probe and the test head causing inaccurate measurements. They worked with the Takeda Riken team to develop a correction table to correct the measurement errors.
The second-generation Bellmac chips had clock speeds exceeding 6.2 MHz, sometimes as high as 9 MHz. This was considered quite fast at the time. The 16-bit Intel 8088 processor that IBM released in its first PC in 1981 had a clock speed of only 4.77 MHz.
Why Bellmac-32 didn’t become mainstream
Despite its promise, Bellmac-32 technology did not gain widespread commercial adoption. According to Condrey, AT&T began to look at equipment maker NCR in the late 1980s and later turned to acquisitions, which meant the company chose to support different chip product lines. By then, Bellmac-32's influence had begun to grow.
“Before Bellmac-32, NMOS dominated the market,” Condry said. “But CMOS changed the landscape because it proved to be a more efficient way to implement it in the fab.”
Over time, this realization reshaped the semiconductor industry. CMOS would become the basis for modern microprocessors, powering the digital revolution in devices like desktop computers and smartphones.
Bell Labs’ bold experiment—using an untested manufacturing process and spanning an entire generation of chip architecture—was a milestone in the history of technology.
As Professor Kang puts it: “We were at the forefront of what was possible. We were not just following an existing path, we were blazing a new trail.” Professor Huang, who later became deputy director of the Singapore Institute of Microelectronics and is also an IEEE Fellow, adds: “This included not only chip architecture and design, but also large-scale chip verification – using CAD but without today’s digital simulation tools or even breadboards (a standard way of checking the circuit design of an electronic system using chips before the circuit components are permanently connected together).”
Condry, Kang and Huang look back on that time fondly and express admiration for the skill and dedication of the many AT&T employees whose efforts made the Bellmac-32 chip family possible.
Post time: May-19-2025