One of the transistor's latestdescendants is the Bell System's30,000-element MAC-4 "com-puter-on-a-chip." It's another ina long line of microelectronicdevelopments that have comefrom Bell Laboratories.The MAC-4 is so efficient that

a program written on it takes25 percent less storage space thanthat required by most othermicrocomputers. Its assemblerlanguage, C, also developed atBell Labs, has features that makeMAC-4 easier to program, debugand maintain. And the MAC-4can handle anything from nibblesto bytes to words with its 4-, 8-, 12-,and 16-bit operations capacity.

Like other one-chip computers,the MAC-4 has sufficientmemoryto support its varied tasks-3000 nibbles of read-only memoryand 200 nibbles of random accessmemory coupled to 34 input/out-put ports.

Fabricated with the latestCMOS technology, the MAC-4needs little power. Thus it is wellmatched to a variety of telecom-munications applications.

It started with the transistorMAC-4 is just one current

example of the many micro-electronic devices to come fromBell Labs since we started the

solid-state revolution with theinvention of the transistor in 1947.Over the past three decades, our

advances in materials, processing,and devices have been vital to-solid-state technology. Theseinclude:* The Junction Transistor* Crystal Pulling* Zone Refining* Field-Effect Transistor* Diffusion* Solar Cell* Oxide Masking* Thermocompression Bonding* Photolithography* Epitaxial Film Process* Magnetic Bubble Memory* Charge-Coupled Device* Semiconductor HeterostructureLaser Used in LightwaveCommunications

* Electron-Beam ExposureSystem

Today and tomorrowToday, we continue to make

important contributions to solid-state technology. For example,we've developed a rugged65,536-bitRAM that can tolerateprocessing faults. Corrections canbe made on the chip itself, so wecan get more usable chips out ofeach manufacturing batch-andthus lower unit costs.

In materials processing, we've

developed a technique for,precisely controlling the growthof successive atomic-layers ofsingle crystal materials. This"molecular beam epitaxy" processis finding increasing use withinBell Labs and elsewhere in theelectronics industry. We've usedit to fabricate a device thatpermits us to double the speedof electrons by channeling theminto crystal layers where theymeet less resistance.

Other advances, in X-raylithography and new resistmaterials, for example, promiseto help place more elements onmicroelectronic devices and thusenhance their ability to performimportant tasks.As the solid-state revolution

continues, these and otherdevelopments from Bell Labs willplay an important part in it.What's important to us is thepromise these advances offer fornew telecommunications productsand services. Like the transistor,MAC-4 and its solid-staterelatives will find more and moreapplications in the nationwidetelecommunications network.

For further information, or to inquireabout employment opportunities, write:Bell Laboratories, Room 3C-30S,600 Mountain Avenue, Murray Hill,N.J. 07974.

BeEl Laboratores

From Science: Service

21 DECEMBER 1979

I e.jr 155oyj.

1355

yfou cv -ouldweteheeamh oierae a hafste cst

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