Reference STATE OF THE ART Stan Augarten

ISBN 0-89919-195-9

Photo of
One of the Most Powerful 16-Bit Microprocessors
The 68000


Although the first 16-bit microprocessor, National Semiconductor's PACE (p. 40), was introduced in 1974, it wasn't until the end of the decade that chip-makers began turning out powerful, general-purpose 16-bit microprocessors. PACE's major drawback was its slowness, the result of being made out of hole-doped transistors; by contrast, the Motorola chip shown on the right is composed of electron-doped transistors, and for this and other reasons is much faster than PACE.

  One of the most versatile and widely used of the 16-bit microprocessors, the 68000 was endowed with intricate internal circuitry that enables it to behave, in many respects, like a 32-bit microprocessor. Although the 68000 absorbs data in 16-bit strings, it can fuse them internally into 32-bit chains, and thereby process chunks of information twice as large. All things being equal, that feature makes it faster and more potent than other 16-bit ICs; it also makes it competitive with true 32-bit chips (like the Hewlett-Packard IC on p. 69).

  To users of microprocessors, however, 16-bit chips offer many more advantages than simply their ability to process longer strings of numbers than their 4- and 8-bit counterparts. They can also address much larger memories - the 68000, for instance, can control some sixteen million bytes, or 16 megabytes, of information, whereas PACE can supervise no more than 64K bytes. The 68000 has many applications, from industrial control equipment to personal computers. It is used, for example, in the most sophisticated model of the Radio Shack TRS-80 computer.

The 68000, shown here on an uncut wafer next to other 68000 chips, can multiply two 16-bit numbers in a mere 3.2 millionths of a second - fifty to sixty times faster than 8-bit microprocessors like the Intel 8080 (p. 36). Eight-bit microprocessors can multiply only by repeated addition, whereas 16-bit microprocessors can contain circuits that enable them to multiply numbers in only a single operation. Actual size of the 68000: 0.246 x 0.281 inches. Photo of


©Copyright Stan Augarten
This book is provided for general reference. The National Museum of American History and the Smithsonian Institution make no claims as to the accuracy or completeness of this work.

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