A Binary Compatibility History Lesson

Early computers were created and programmed individually for each customer, and there was no thought of being able to run the same program on different machines. But in 1964, IBM introduced the System/360 family of computers, ranging from a minicomputer with 24KB of memory to a supercomputer built for the North American missile defense system. Despite the considerable differences among these machines, they all used the same set of instructions and could be considered binary compatible.

A finished program could run successfully on a small minicomputer or a large mainframe, even though the two machines actually carried out the instructions in different ways. High-end machines could quickly and efficiently do multiplication in hardware, whereas low-end machines that lacked the special hardware instead implemented the instruction in microcode -- doing multiplication by means of repeated addition, for example. According to some reports, it was rumored that the smallest machines did addition by repeated increments.

Once the principle of binary compatibility was established, the stage was set for a company other than IBM to produce a machine that could run that same software, and that's exactly what happened. Gene Amdahl, the principal architect of System/360, left IBM in 1970 to form his own company. Instead of creating a direct rival to IBM's comprehensive computer systems, Amdahl created lower-priced computers that could run the same software. In other words, he designed the first mainframe clones, then known as "plug-compatibles." In 1975, Amdahl Corp. shipped its first computer, the Amdahl 470 V/6.

When the microcomputer revolution hit in the late 1970s and early '80s, a similar chain of events unfolded. Early micros were different from one another, and each brand had its own quirks and unique capabilities. After IBM introduced the PC in 1982 with an open architecture, a number of competitors arose, but slight differences among their products meant that programs for an IBM machine still might not run properly on other computers. Compaq Computer Corp. created the first true PC clone in 1983, as Amdahl had for the mainframe, and the rest is history.

Copyright © 2002 IDG Communications, Inc.

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