The IBM Personal Computer, model number 5150, was announced on August 12, 1981. It was IBM’s entry into a market then dominated by machines like the Apple II and the various CP/M computers, and it was built quickly by a small team in Boca Raton, Florida, using components and software bought from outside vendors rather than designed in-house. The machine used an Intel 8088 microprocessor running at 4.77 MHz, and its operating system was supplied by Microsoft and sold as PC DOS.
What set the 5150 apart was not raw novelty but openness. IBM published the machine’s complete technical details in the IBM Personal Computer Technical Reference (document 6025008, dated August 1981). That manual documented the system board, the bus, the adapter cards, and the interrupt structure in full, and it included the complete assembly-language source listing of the system BIOS. The Technical Reference states its purpose plainly: it “provides hardware and software interface information to allow you to design products that interface to the IBM Personal Computer.” In other words, IBM handed third parties everything they needed to build add-in cards and compatible software.
This decision had enormous consequences. Because the architecture was documented and built from standard parts, a thriving ecosystem of expansion cards, peripherals, and software grew up around the PC almost immediately. The same openness that fed that ecosystem, however, also told competitors exactly how the machine worked. The one piece IBM could protect was the copyrighted BIOS code printed in the manual, and the rest of the personal-computer industry would spend the next few years working out how to reproduce its behavior legally.
The 5150 was not the first personal computer, nor the fastest, nor the cheapest. Its importance lies in becoming the reference design that the rest of the industry standardized on. Within a few years “IBM compatible” was the phrase that defined the mainstream of personal computing, and the architecture first described in that 1981 Technical Reference outlived IBM’s own dominance of the market it created.